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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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Condensing boiler - odd installation
I've read most of the condensing boiler discussions in this group and as a
result decided to fit a standard boiler - mainly because of not being able to upgrade old radiators to work with the lower return temperature. I was helping a friend select a new boiler and told them the same story but then realised I might be missing something. They have a heated swimming pool via a heat exchanger plumbed to the CH. What if they put the heat exchanger on the return flow? That would drop the return temperature even if the old radiators didn't. Am I being too simple minded? mikej |
#2
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Condensing boiler - odd installation
I've read most of the condensing boiler discussions in this group and as a
result decided to fit a standard boiler - mainly because of not being able to upgrade old radiators to work with the lower return temperature. Unfortunately, you are misinformed. Although condensing boilers can take additional advantage of lower return temperatures, they are still more efficient than a traditional boiler at high return temperatures too. There is absolutely no need to replace radiators when upgrading to a condensing boiler. The additional economic benefit is too slight to be worth doing unless the radiators are being replaced anyway. The condensing boiler will usually be capable of maintaining the "standard" 82C flow temperature. (My Bosch Worcester Greenstar II 28HE claims to run up to 88C flow temperatures). Also, radiators are sized for outside temperatures of -1C. As this is much lower than your average temperature, your radiators are usually oversized anyway and the condensing boiler can turn down the return temperature using its internal logic. What if they put the heat exchanger on the return flow? That would drop the return temperature even if the old radiators didn't. Am I being too simple minded? This heat exchanger should be connected between flow and return as normal via a zone valve. Christian. |
#3
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Condensing boiler - odd installation
In article , mike.james
writes I've read most of the condensing boiler discussions in this group and as a result decided to fit a standard boiler - mainly because of not being able to upgrade old radiators to work with the lower return temperature. Fair enough, but for most of the year, the reduced output from your rads would be enough to heat your home with the boiler set to say 60 or 70 degree flow (50 deg return) and you would have had the benefit of condensing action. Then, in the coldest part of the year you could jack the flow temp up to 80 degrees (with the boiler stat) and get the same heat from the rads as you would with a conventional boiler. For this period though you would lose the benefit of condensing action, but hopefully only for the coldest month or two of the year. I was helping a friend select a new boiler and told them the same story but then realised I might be missing something. They have a heated swimming pool via a heat exchanger plumbed to the CH. What if they put the heat exchanger on the return flow? That would drop the return temperature even if the old radiators didn't. Am I being too simple minded? mikej Sadly, I think there is a flaw here and it revolves around the boiler being optimised (by design) to run at (say) a 20 degree temperature difference, which I don't think is optimal for your system. I assume you want to keep an 80 degree flow to use existing rads, but then want a 50 degree return to take advantage of condensing boiler action. That's a 30 degree system drop which I don't think the boiler heat exchanger will be capable of overcoming on the heating cycle; as it will be designed for 20. If you slow the flow to promote a 30 degree rise I think you will get a low flow alarm from the boiler. If you instead run with a 70 degree flow, with 10 degree drop on rads and then a 10 degree drop on the heat exchanger you will have the requisite 20 degree drop, but you will only have a 65 degree mean in the rads. This is better than the full condensing case, but worse than the 75 degree mean of an 80/70 system (13% worse). So, nice try, but I think if you want to keep your rads, you would be better going with the idea at the top and making do with the non condensing action for part of the year. It's what I've done (on a new system) to keep a reasonable compromise on rad sizes. -- fred |
#4
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Condensing boiler - odd installation
"Christian McArdle" wrote in message t... I've read most of the condensing boiler discussions in this group and as a result decided to fit a standard boiler - mainly because of not being able to upgrade old radiators to work with the lower return temperature. Unfortunately, you are misinformed. Possibly. Although condensing boilers can take additional advantage of lower return temperatures, they are still more efficient than a traditional boiler at high return temperatures too. But there efficiency drops as the return temperature goes up. And efficiency alters the time to repay - so with an old installation it might make a difference. What if they put the heat exchanger on the return flow? That would drop the return temperature even if the old radiators didn't. Am I being too simple minded? This heat exchanger should be connected between flow and return as normal via a zone valve. Thanks for the reply - but why wouldn't it improve the efficiency to put it in the return. mikej |
#5
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Condensing boiler - odd installation
On Fri, 24 Oct 2003 14:35:24 +0100, "mike.james"
wrote: I've read most of the condensing boiler discussions in this group and as a result decided to fit a standard boiler - mainly because of not being able to upgrade old radiators to work with the lower return temperature. No actually it's not a problem. It is true that condensing boilers perform more efficiently at lower return temperatures and especially below the 54 degree dew point. However, there are two points he - A condensing boiler will generally perform more efficiently than a non condensing one anyway because it is likely to have a larger heat exchanger. - System design is done around an outside temperature of -1 or -3 degrees. An old radiator system should have been sized assuming that the outside temperature is -1 worst case and that the boiler flow and return are 82 and 70 degrees respectively (a conventional boiler). However, for most of the heating season, the outside temperature is some degrees higher and so the radiator outputs and consequently the boiler output will not need to be so high. A condensing boiler normally modulates and reduces its output accordingly, so naturally will tend towards lower operating temperatures and greater efficiency. When I refurbished my system, I calculated all the heat requirements for the rooms and discovered that in two rooms that the radiators were undersized even for 82 degree operation. These rooms had always been on the chilly side on very cold days. In other rooms, I found that they were quite oversized. I then recalculated everything and discovered that by buying two new radiators and moving others around, they could all be run at 70 degrees flow, so I did the changes. However, had everything been adequately sized in the first place, I would probably not have bothered. In other words, it is still worth installing a condensing boiler anyway, even if you don't alter the radiators. I was helping a friend select a new boiler and told them the same story but then realised I might be missing something. They have a heated swimming pool via a heat exchanger plumbed to the CH. What if they put the heat exchanger on the return flow? That would drop the return temperature even if the old radiators didn't. Am I being too simple minded? mikej Yes it would, but it's the wrong way to go about things. The heat exchanger in the boiler is able to manage a certain uplift in temperature at a given heat input from the burner. Cooling the return water would have the effect of also reducing the flow temperature quite a bit so you wouldn't get the needed output from the radiators. The heat exchanger for the pool should go across the flow and return of the boiler in the same way as the radiators and HW cylinder, and the flow through it controlled by a zone valve with some form of thermostat and/or timer. ..andy To email, substitute .nospam with .gl |
#6
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Condensing boiler - odd installation
In article ,
Mike.james wrote: I've read most of the condensing boiler discussions in this group and as a result decided to fit a standard boiler - mainly because of not being able to upgrade old radiators to work with the lower return temperature. Even with the normal return temperature you'll probably find that most condensers have an efficiency advantage. If you look at page 3 of the Keston Celsius leaflet http://www.keston.co.uk/downloads/pdf/cel25-b.pdf you'll see this. Remember that the return temp will be lower whenever the system starts from cold and during the spring and autumn when the boiler only cuts in periodically. -- Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm |
#7
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Condensing boiler - odd installation
On Fri, 24 Oct 2003 16:17:54 +0100, "mike.james"
wrote: But there efficiency drops as the return temperature goes up. Yes, but it will still be more efficient than an old boiler. If you compare new conventional with new condensing, the new condensing will be more efficient, averaged over the year than the new conventional because the condensing model has the opportunity to operate at lower temperatures in (say) the autumn and spring. The conventional boiler will always operate at the higher fixed temperature. And efficiency alters the time to repay - so with an old installation it might make a difference. Yes, but you will still get better efficiency from a new condensing boiler than a new conventional one and both will be better than an old boiler. How long the payback is is difficult to say. If you are making the comparison by looking at the cost of changing all the radiators to get as much efficiency as you can out of a new condensing boiler, the payback is likely to be extremely long and not worth the effort. For me, it was worth doing because I could achieve the desired result without having to change *all* the radiators. What if they put the heat exchanger on the return flow? That would drop the return temperature even if the old radiators didn't. Am I being too simple minded? This heat exchanger should be connected between flow and return as normal via a zone valve. Thanks for the reply - but why wouldn't it improve the efficiency to put it in the return. In a way, but the flow temperature would be substantially reduced and probably not give the required outputs from radiators ..andy To email, substitute .nospam with .gl |
#8
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Condensing boiler - odd installation
But there efficiency drops as the return temperature goes up.
And efficiency alters the time to repay - so with an old installation it might make a difference. All boilers drop in thermodynamic efficiency as the return temperature goes up. The differences between a condensing one and a traditional one a 1. The condensing type is ALWAYS much more efficient than the traditional type at ANY flow or return temperature. 2. The condensing type has even greater efficiency still at lower return temperatures. Don't get bogged down thinking about item 2, when item 1 alone is enough to justify a condensing boiler. Remember also, that condensing boilers are intelligent and will drop the return temperature if they detect they can get away with it. Thanks for the reply - but why wouldn't it improve the efficiency to put it in the return. It would increase the instantaneous thermodynamic efficiency. However, it will cost much more to run, as the controls would not actually be keeping everything at the correct temperature. There is more money to be saved ensuring everything is only heated as much as is required, than by trying to get an extra 5% on the thermodynamic efficiency. Your scheme is likely to end up heating the swimming pool to higher temperatures than you wish, which will cost you a fortune, even if that heating was done efficiently. Christian. |
#9
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Condensing boiler - odd installation
"Christian McArdle" wrote in message t... I've read most of the condensing boiler discussions in this group and as a result decided to fit a standard boiler - mainly because of not being able to upgrade old radiators to work with the lower return temperature. Unfortunately, you are misinformed. Although condensing boilers can take additional advantage of lower return temperatures, they are still more efficient than a traditional boiler at high return temperatures too. There is absolutely no need to replace radiators when upgrading to a condensing boiler. The additional economic benefit is too slight to be worth doing unless the radiators are being replaced anyway. The condensing boiler will usually be capable of maintaining the "standard" 82C flow temperature. (My Bosch Worcester Greenstar II 28HE claims to run up to 88C flow temperatures). Also, radiators are sized for outside temperatures of -1C. As this is much lower than your average temperature, your radiators are usually oversized anyway and the condensing boiler can turn down the return temperature using its internal logic. What if they put the heat exchanger on the return flow? That would drop the return temperature even if the old radiators didn't. Am I being too simple minded? This heat exchanger should be connected between flow and return as normal via a zone valve. Modern condensing boilers have load compensation control that takes care of rads sized to 80C. The big market is in replacement boilers and the makers designed to suit. The only case where you don't fit a condensing boiler is when the plume is a nuisance or there is no drain connection for the condensate. Otherwise "always" fit a condesning or "no-flame" boiler. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
#10
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Condensing boiler - odd installation
"fred" wrote in message ... In article , mike.james writes I've read most of the condensing boiler discussions in this group and as a result decided to fit a standard boiler - mainly because of not being able to upgrade old radiators to work with the lower return temperature. Fair enough, but for most of the year, the reduced output from your rads would be enough to heat your home with the boiler set to say 60 or 70 degree flow (50 deg return) and you would have had the benefit of condensing action. Then, in the coldest part of the year you could jack the flow temp up to 80 degrees (with the boiler stat) and get the same heat from the rads as you would with a conventional boiler. For this period though you would lose the benefit of condensing action, but hopefully only for the coldest month or two of the year. I was helping a friend select a new boiler and told them the same story but then realised I might be missing something. They have a heated swimming pool via a heat exchanger plumbed to the CH. What if they put the heat exchanger on the return flow? That would drop the return temperature even if the old radiators didn't. Am I being too simple minded? mikej Sadly, I think there is a flaw here and it revolves around the boiler being optimised (by design) to run at (say) a 20 degree temperature difference, which I don't think is optimal for your system. I assume you want to keep an 80 degree flow to use existing rads, but then want a 50 degree return to take advantage of condensing boiler action. That's a 30 degree system drop which I don't think the boiler heat exchanger will be capable of overcoming on the heating cycle; as it will be designed for 20. If you slow the flow to promote a 30 degree rise I think you will get a low flow alarm from the boiler. Modern condesning boilers have load compensation control that lowers the return temp.by modulating the burner, to suit inside conditions. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
#11
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Condensing boiler - odd installation
"mike.james" wrote in message ... "Christian McArdle" wrote in message t... I've read most of the condensing boiler discussions in this group and as a result decided to fit a standard boiler - mainly because of not being able to upgrade old radiators to work with the lower return temperature. Unfortunately, you are misinformed. Possibly. Not possibly, he was. Although condensing boilers can take additional advantage of lower return temperatures, they are still more efficient than a traditional boiler at high return temperatures too. But there efficiency drops as the return temperature goes up. That is true. And efficiency alters the time to repay - so with an old installation it might make a difference. Modern condesning boilers have load compensation control that lowers the return temp.by modulating the burner, to suit inside conditions. What if they put the heat exchanger on the return flow? That would drop the return temperature even if the old radiators didn't. Am I being too simple minded? This heat exchanger should be connected between flow and return as normal via a zone valve. Thanks for the reply - but why wouldn't it improve the efficiency to put it in the return. mikej Please look at some basic heating books. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
#12
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Condensing boiler - odd installation
"Christian McArdle" wrote in message t... But there efficiency drops as the return temperature goes up. And efficiency alters the time to repay - so with an old installation it might make a difference. All boilers drop in thermodynamic efficiency as the return temperature goes up. The differences between a condensing one and a traditional one a 1. The condensing type is ALWAYS much more efficient than the traditional type at ANY flow or return temperature. 2. The condensing type has even greater efficiency still at lower return temperatures. Don't get bogged down thinking about item 2, when item 1 alone is enough to justify a condensing boiler. Remember also, that condensing boilers are intelligent and will drop the return temperature if they detect they can get away with it. Not all. some are quite dumb and have on-off control. My condensing boiler does not modulate with a one fixed burner rate. I control it by using an outside weather compensator, which reduces the return temp to suit . The compensator has boiler anti-cycle control. Those with modulating load compensation control are ones to fit on an existing system. Thanks for the reply - but why wouldn't it improve the efficiency to put it in the return. It would increase the instantaneous thermodynamic efficiency. However, it will cost much more to run, as the controls would not actually be keeping everything at the correct temperature. There is more money to be saved ensuring everything is only heated as much as is required, than by trying to get an extra 5% on the thermodynamic efficiency. Your scheme is likely to end up heating the swimming pool to higher temperatures than you wish, which will cost you a fortune, even if that heating was done efficiently. From what I understand he wants a plate heat exchanger on the boilers return to lower the return temp further, that would only work when the CH is on. On a fixed rate boiler this will increase the flow/return delta T alarmingly. On a load compensation boiler the flow temp may be reduced too much as the boiler aims to keep the delta T and may think the house is up to temp. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
#13
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Condensing boiler - odd installation
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#14
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Condensing boiler - odd installation
In article ,
mike.james wrote: I've read most of the condensing boiler discussions in this group and as a result decided to fit a standard boiler - mainly because of not being able to upgrade old radiators to work with the lower return temperature. Surly this would only be so on the coldest of days - when the system was working at less than full capacity the benefits of a condensing boiler would apply? -- *Am I ambivalent? Well, yes and no. Dave Plowman London SW 12 RIP Acorn |
#15
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Condensing boiler - odd installation
"fred" wrote in message ... In article , IMM abuse- writes If you slow the flow to promote a 30 degree rise I think you will get a low flow alarm from the boiler. Modern condesning boilers have load compensation control that lowers the return temp, by modulating the burner, to suit inside conditions. Which would result in a failure to maintain a 30 degree uplift . . . FYI, the keston will maintain full power where there is a low return temp, but will flag a low flow alarm Depends on how the software is programmed. Not all do it the same. Some attempt to maintain the delta T and the lowest return temp as possible. Not difficult. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
#16
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Condensing boiler - odd installation
"mike.james" wrote:
"Christian McArdle" wrote in message t... I've read most of the condensing boiler discussions in this group and as a result decided to fit a standard boiler - mainly because of not being able to upgrade old radiators to work with the lower return temperature. Unfortunately, you are misinformed. Possibly. Although condensing boilers can take additional advantage of lower return temperatures, they are still more efficient than a traditional boiler at high return temperatures too. But there efficiency drops as the return temperature goes up. And efficiency alters the time to repay - so with an old installation it might make a difference. What if they put the heat exchanger on the return flow? That would drop the return temperature even if the old radiators didn't. Am I being too simple minded? This heat exchanger should be connected between flow and return as normal via a zone valve. Thanks for the reply - but why wouldn't it improve the efficiency to put it in the return. mikej The issue is not so much of efficiency but of control - say you want to heat the pool and not the house? -- Ed Sirett - Property maintainer and registered gas fitter. The FAQ for uk.diy is at www.diyfaq.org.uk Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html |
#17
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Condensing boiler - odd installation
Thanks for all the comments - as always the subject of condensing boilers
seems to stir a reply :-) I appreciate the "condensing boiler is always more efficient" argument but my friend is running a small hotel and been quoted (rough figures) £800 for a conventional boiler to do the job and £1600 for a condensing boiler. So if the efficiency advantage isn't fairly large the payback time is going to be long. It seems that there really is a choice to be made here. As to my "silly" idea of putting their pool heat exchanger in the return loop I'm still not sure how silly it really is. The point made about control rather than efficiency is a good one but control could be added with couple of valves and a thermostat. I can also see that there is a problem with a modulating boiler thinking that the house was still cold because the pool exchanger was still lowering the temperature and I'm still thinking about this one. Given the house has termo valves on all the radiators and so does the pool - how does this change things? But after saying this I now think that the general vote of "it isn't worth the gain in efficiency for the complexity increase" - but I thought it was a nice idea. mikej |
#18
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Condensing boiler - odd installation
mike.james wrote:
Thanks for all the comments - as always the subject of condensing boilers seems to stir a reply :-) I appreciate the "condensing boiler is always more efficient" argument but my friend is running a small hotel and been quoted (rough figures) £800 for a conventional boiler to do the job and £1600 for a condensing boiler. So if the efficiency advantage isn't fairly large the payback time is going to be long. It seems that there really is a choice to be made here. I have the same problem justifying a condensing boiler. Conventional combis are cheap and easy to fit. The best case difference in efficiency afaik is no more than 6%. This would save me perhaps £25 a year. So as far as I'm concerned the condenser is not viable esp as I don't intend to stay in this house forever and I don't think having a condenser vs. normal combi would help to sell the house at all.. As to my "silly" idea of putting their pool heat exchanger in the return loop I'm still not sure how silly it really is. If you were to do this it would be equivalent to putting radiators in series which is just not done. |
#19
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Condensing boiler - odd installation
"mike.james" wrote:
= Thanks for all the comments - as always the subject of condensing boile= rs seems to stir a reply :-) = I appreciate the "condensing boiler is always more efficient" argument = but my friend is running a small hotel and been quoted (rough figures) =A3800 for a conventional boiler to do the job and =A31600 for a conden= sing boiler. So if the efficiency advantage isn't fairly large the payback t= ime is going to be long. It seems that there really is a choice to be made her= e. = This is silly. There is no way that condensing boiler are double the price. Typical increase for a condensing boiler is around a couple of hundred more. = [Vaillant have not caught up with this yet and are still trying to flog condensing boiler against a 400 quid margin 8-(] Whilst the 1600 would seem resonable for somthing like a Keston C40 or C55. I have my doubts that you can get 40kW of conventional boiler for 800. Perhaps they are thinking of "bolting" [1] a couple of really cheap conventional boilers together - but that's not comparing like for like. = Actually 1600 would be fair for a couple of C25s bolted together and that would give more control and reliability options. [1] Not literally 8-). = -- = Ed Sirett - Property maintainer and registered gas fitter. The FAQ for uk.diy is at www.diyfaq.org.uk Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html |
#20
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Condensing boiler - odd installation
"mike.james" wrote in message ... Thanks for all the comments - as always the subject of condensing boilers seems to stir a reply :-) I appreciate the "condensing boiler is always more efficient" argument but my friend is running a small hotel and been quoted (rough figures) £800 for a conventional boiler to do the job and £1600 for a condensing boiler. So if the efficiency advantage isn't fairly large the payback time is going to be long. It seems that there really is a choice to be made here. As to my "silly" idea of putting their pool heat exchanger in the return loop I'm still not sure how silly it really is. The point made about control rather than efficiency is a good one but control could be added with couple of valves and a thermostat. I can also see that there is a problem with a modulating boiler thinking that the house was still cold because the pool exchanger was still lowering the temperature and I'm still thinking about this one. Given the house has termo valves on all the radiators and so does the pool - how does this change things? But after saying this I now think that the general vote of "it isn't worth the gain in efficiency for the complexity increase" What general vote? There is little complexity increase. £800 to £1600. he is being ripped off. Condensing boilers cost little over regular boilers these days. Get another quote. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
#21
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Condensing boiler - odd installation
"BillR" wrote in message ... mike.james wrote: Thanks for all the comments - as always the subject of condensing boilers seems to stir a reply :-) I appreciate the "condensing boiler is always more efficient" argument but my friend is running a small hotel and been quoted (rough figures) £800 for a conventional boiler to do the job and £1600 for a condensing boiler. So if the efficiency advantage isn't fairly large the payback time is going to be long. It seems that there really is a choice to be made here. I have the same problem justifying a condensing boiler. Conventional combis are cheap and easy to fit. The best case difference in efficiency afaik is no more than 6%. This would save me perhaps £25 a year. 6%?? look at http://www.sedbuk.com More like 12% according to sedbuk. If the system is engineered to take advantage of a condensing boiler, then more like 25%. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
#22
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Condensing boiler - odd installation
"Ed Sirett" wrote in message ... "mike.james" wrote: This is silly. There is no way that condensing boiler are double the price. Its an Ideal Mexico Super CF4140 - 140,000 BTU - 41kw £872 v Keston C55 (55Kw) £ 1,548.89 or the C40 (40Kw) at £ 1,360.90 (Prices I've got from pumbworld which don't correspond to the prices quoted in the installation which are up by about 10-20% which makes the gap bigger) mikej |
#23
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Condensing boiler - odd installation
"IMM" wrote in message ... What general vote? There is little complexity increase. £800 to £1600. he is being ripped off. Condensing boilers cost little over regular boilers these days. Get another quote. Are you saying pumbworld or similar (checked other online prices) are ripping us off? (See other post for quote) mikej |
#24
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Condensing boiler - odd installation
"IMM" wrote in message ... 6%?? look at http://www.sedbuk.com More like 12% according to sedbuk. If the system is engineered to take advantage of a condensing boiler, then more like 25%. Now this brings me back to my original point. What does "engineered to take advantage" mean - lower return temperatures? Hence my "silly" idea of putting the pool's heat exchanger in the return flow. mikej |
#25
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Condensing boiler - odd installation
On Sun, 26 Oct 2003 10:44:40 -0000, "mike.james"
wrote: "Ed Sirett" wrote in message ... "mike.james" wrote: This is silly. There is no way that condensing boiler are double the price. Its an Ideal Mexico Super CF4140 - 140,000 BTU - 41kw £872 Poor choice. The SEDBUK seasonal efficiency figure for this one is 78.6%. In other words, it only *just* scrapes into the minimum legal requirements for efficiency according to the building regulations. Fairly shortly, the minimum will be increased so this type of product will be off the market and is probably why the price per kW is relatively low. The manufacturers, knowing that the lifetime is limited, are getting what they can for the remainder of its (short) market lifetime. As far as I can see, it isn't on their web site any more, so that should provide a clue. Also, note that you are not comparing apples with apples. These Ideal products are basic, non-system boilers and do not have a pump. This particular model is also conventional flue. For a new installation, this does not really make sense because of the need to provide appropriate room ventilation (= cold air from outside) and the likelhood to have to buy a flue system to go with it, pushing up the price. v Keston C55 (55Kw) £ 1,548.89 or the C40 (40Kw) at £ 1,360.90 Both of these products come in at at around 90% seasonal efficiency, include a pump and can work with cheap plastic waste pipe as a flue. All of this is before the difference in energy saving is taken into account. (Prices I've got from pumbworld which don't correspond to the prices quoted in the installation which are up by about 10-20% which makes the gap bigger) mikej ..andy To email, substitute .nospam with .gl |
#26
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Condensing boiler - odd installation
On Sun, 26 Oct 2003 10:47:21 -0000, "mike.james"
wrote: "IMM" wrote in message ... 6%?? look at http://www.sedbuk.com More like 12% according to sedbuk. If the system is engineered to take advantage of a condensing boiler, then more like 25%. Now this brings me back to my original point. What does "engineered to take advantage" mean - lower return temperatures? Hence my "silly" idea of putting the pool's heat exchanger in the return flow. mikej I think that you are missing the point. It is the case that a lower return temperature improves the efficiency of a condensing boiler, however this is not the complete story. Any boiler heat exchanger will have a maximum temperature differential that it can support - for a condesning boiler around 20-25 degrees, for a conventional one around 10-12. This is designed around firing and flow rates as well. The heat transfer through emitters such as the radiators or the pool heat exchanger is proportional to the temperature difference and the flow rate. This is given by the equation energy = mass x specific heat x temperature rise or fall. If you connect the radiators, as you should, across the boiler flow and return, they will receive the full temperature drop, as would the pool heat exchanger. Typically, you would have a valve arrangement to balance the flow between the two and hence share the heat. If the requirement for the pool heat exchanger is large, one might even have separate pumps for the heating and this; the effect of which would be to increase flow through the boiler when there is more heat demand. In a modulating boiler, this would cause the boiler to modulate upwards while maintaining the same temperature drop. Some condensing boilers with built in single pump even control the pump speed as the power requirements change. If you connect in series, the radiators and the heat exchanger will get the same flow rate (by definition). The temperature drop will be split between them and so each will only get a proportion and not be able to run at full load. The boiler won't be able to increase its tremperature difference to deal with this, and so the only way to get more heat output would be to increase the flow. Unfortunately, this will not usually be possible because the radiator and pool heat exchanger will probably not be able to take that. Moreover, there would be no way to balance heat between the two. You have to look at the system as a whole - you can't just focus on one aspect and assume that everything else falls into place. ..andy To email, substitute .nospam with .gl |
#27
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Condensing boiler - odd installation
"Andy Hall" wrote in message ... Its an Ideal Mexico Super CF4140 - 140,000 BTU - 41kw £872 Poor choice. The SEDBUK seasonal efficiency figure for this one is 78.6%. In other words, it only *just* scrapes into the minimum legal requirements for efficiency according to the building regulations. Fairly shortly, the minimum will be increased so this type of product will be off the market and is probably why the price per kW is relatively low. The manufacturers, knowing that the lifetime is limited, are getting what they can for the remainder of its (short) market lifetime. As far as I can see, it isn't on their web site any more, so that should provide a clue. Very good point. One I can use in getting them to requote with a better conventional boiler. Also, note that you are not comparing apples with apples. These Ideal products are basic, non-system boilers and do not have a pump. This particular model is also conventional flue. For a new installation, this does not really make sense because of the need to provide appropriate room ventilation (= cold air from outside) and the likelhood to have to buy a flue system to go with it, pushing up the price. Ah but the flue is there - it isn't a new installation. v Keston C55 (55Kw) £ 1,548.89 or the C40 (40Kw) at £ 1,360.90 Both of these products come in at at around 90% seasonal efficiency, include a pump and can work with cheap plastic waste pipe as a flue. All of this is before the difference in energy saving is taken into account. Well the flue is there - and they are charging to take it down if the Keston goes in! (So is the pump.) I personally like the spec of the Keston - I'll see if they can quote for a different conventional boiler. mikej |
#28
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Condensing boiler - odd installation
Now this brings me back to my original point. What does "engineered to take advantage" mean - lower return temperatures? Hence my "silly" idea of putting the pool's heat exchanger in the return flow. mikej I think that you are missing the point. No I'm not if you read my earlier posts you will see that I've agreed that the situation is complicated and I've more or less given up on the idea. All I'm asking for is clarification of what "engineered to take advantage" means in the previous post. As you your reply - I follow what you are saying but I don't think the outcome is conclusive because the pool isn't like a room heated by a radiator - it doesn't have to come up to temperature quickly (and it has a much bigger "thermal inertia"). Imagine a standard setup (forget the pool for a moment) and the return temperature isn't low enough to get to the dew point i.e. boiler not working at maximum efficiency. Now put pool heat exchanger in return flow. Pool water is very cold by comparison with return water flow and should drop its temperature. It might even be enough to make the boiler work at its most efficient. As its in the return it can't alter the efficiency or temperature of the house radiators unless the flow temperature drops. The heat output from the radiators can't be changed by this because the boiler will just work harder to lift the outflow temperature - this must be possible because its how the boiler is designed to work. I.e. if the house radiators were working as required the return temperature would be exactly what we have with the pool heat exchanger in the circuit. The only down side is that that pool heat exchanger isn't as efficient because its inflow water is cooler - but who cares? The pools heat cycle is only 4 - 6 hours each day. So just increase it to whatever it takes - 12 hours even. As to what happens when the house CH isn't needed - just switch it back to a flow and return connection as standard. For a modulating boiler I can see that there is the additional problem of the boiler always thinking that the house is cold but then there are room stats for that. mikej |
#29
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Condensing boiler - odd installation
On Sun, 26 Oct 2003 11:40:14 -0000, "mike.james"
wrote: "Andy Hall" wrote in message .. . Its an Ideal Mexico Super CF4140 - 140,000 BTU - 41kw £872 Poor choice. The SEDBUK seasonal efficiency figure for this one is 78.6%. In other words, it only *just* scrapes into the minimum legal requirements for efficiency according to the building regulations. Fairly shortly, the minimum will be increased so this type of product will be off the market and is probably why the price per kW is relatively low. The manufacturers, knowing that the lifetime is limited, are getting what they can for the remainder of its (short) market lifetime. As far as I can see, it isn't on their web site any more, so that should provide a clue. Very good point. One I can use in getting them to requote with a better conventional boiler. Which would put the difference between this and a much more efficient condensing model even less. Don't forget also, that the manufacturers run loyalty schemes for the trade. Go into any heating merchants and pick up one of the trade magazines and you will find the manufacturers offering tools, cash backs, designer clothing and trips to the sun. Then ask yourself whether the installer is acting in your interest or his. You will also find that installers tend to stick with what they know and what they have always done. This could be another reason why you are being offered ancient technology. Also, note that you are not comparing apples with apples. These Ideal products are basic, non-system boilers and do not have a pump. This particular model is also conventional flue. For a new installation, this does not really make sense because of the need to provide appropriate room ventilation (= cold air from outside) and the likelhood to have to buy a flue system to go with it, pushing up the price. Ah but the flue is there - it isn't a new installation. Don't assume that it would not need to be replaced even for a new CF boiler - it may not be up to spec. v Keston C55 (55Kw) £ 1,548.89 or the C40 (40Kw) at £ 1,360.90 Both of these products come in at at around 90% seasonal efficiency, include a pump and can work with cheap plastic waste pipe as a flue. All of this is before the difference in energy saving is taken into account. Well the flue is there - and they are charging to take it down if the Keston goes in! (So is the pump.) ..... and it's reasonably new? I personally like the spec of the Keston - I'll see if they can quote for a different conventional boiler. I think that you have to make your own decision, but I don't think that your logic is quite correct. There doesn't seem any point to me in replacing ancient technology with new ancient technology when you can have much improved energy usage with a new condensing boiler. If you take a look at the Sedbuk site, they indicate that you can easily save £150 per annum on energy in a large house installation when changing from an older boiler of about 65% efficiency. They are about right - I've done it - and that is with with a 25kW boiler. If you factor up to a 40kW boiler, the saving could be £250, although this is for going from a 65% efficient product to a 90% efficient one. For a comparison between a 78% - 80% efficient conventional boiler you would approximately split the difference, so say £100-150 pa..... At current gas prices, I would be surprised if cost recovery were not achieved in 5 years, and there is no evidence to suggest that gas prices will drop...... ..andy To email, substitute .nospam with .gl |
#30
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Condensing boiler - odd installation
"mike.james" wrote in message ... "Ed Sirett" wrote in message ... "mike.james" wrote: This is silly. There is no way that condensing boiler are double the price. Its an Ideal Mexico Super CF4140 - 140,000 BTU - 41kw £872 v Keston C55 (55Kw) £ 1,548.89 or the C40 (40Kw) at £ 1,360.90 (Prices I've got from pumbworld which don't correspond to the prices quoted in the installation which are up by about 10-20% which makes the gap bigger) mikej Ideal ICOS "system" boiler £740.25 Including VAT Ideal ICOS "heating" boiler £675.63 Including VAT Two ICOS condensing boilers at approx 24kW each is about the same price. So may as well get two of them and couple them up. System boilers come with pressure vessel and pump. http://www.discountedheating.co.uk/ --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
#31
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Condensing boiler - odd installation
"Andy Hall" wrote in message Very good point. One I can use in getting them to requote with a better conventional boiler. Which would put the difference between this and a much more efficient condensing model even less. But it would be nice if the gap was narrowed by a price reduction not a price increase. Ah but the flue is there - it isn't a new installation. Don't assume that it would not need to be replaced even for a new CF boiler - it may not be up to spec. The flue is fine and the Mexico is replacing a similar boiler so installation costs are less. I think that you have to make your own decision, but I don't think that your logic is quite correct. There doesn't seem any point to me in replacing ancient technology with new ancient technology when you can have much improved energy usage with a new condensing boiler. I agree but my friend is more interested in money than technology. If you take a look at the Sedbuk site, they indicate that you can easily save £150 per annum on energy in a large house installation when changing from an older boiler of about 65% efficiency. They are about right - I've done it - and that is with with a 25kW boiler. If you factor up to a 40kW boiler, the saving could be £250, although this is for going from a 65% efficient product to a 90% efficient one. For a comparison between a 78% - 80% efficient conventional boiler you would approximately split the difference, so say £100-150 pa..... In my friends world this gives about 5 to 8 years to pay back the invesment. As he is thinking of selling up in at most 5 years you can see that I can't swing the argument on cost - which is all he seems to be interested in. At current gas prices, I would be surprised if cost recovery were not achieved in 5 years, and there is no evidence to suggest that gas prices will drop...... This is a better argument, if rising prices could be better :-) mikej |
#32
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Condensing boiler - odd installation
"mike.james" wrote in message ... "IMM" wrote in message ... 6%?? look at http://www.sedbuk.com More like 12% according to sedbuk. If the system is engineered to take advantage of a condensing boiler, then more like 25%. Now this brings me back to my original point. What does "engineered to take advantage" mean - lower return temperatures? Yes. Larger rads. Hence my "silly" idea of putting the pool's heat exchanger in the return flow. Your idea will only work when heating is on, as the heat exchanger is on the return pipe, which is "silly". As Andy and myself have highlighted, a boiler should work "inside" a flow/return temp difference. Outside this for sustained periods can cause big problems. When control is on the boiler you are fooling it and it may not react the way you expect, or want. Look at a swimming pool. What is the ideal temp? 23C? Most of the time the return temp from the pool will be between 15-22C, cold enough for excellent efficiencies in a condensing boiler. Assuming the pool is indoors. If outdoors then the return temps may be very much lower. The boiler will be operating all night to raise it a degree or two. Most swimming pool have the pool heated all day and the temp setback at night. It is knowing when time the night setback has to return to normal day temp, as it will take hours to raise the temp. I would go for basic condensing boilers, and have stand-alone control for the pool heater, DHW and CH. This is a commercial setup, so control it as such. The likes of the ICOS and Keston Celsius are for domestic properties. B&Q have for sale the Ravenheat CSI for £400. This is basic. Two of these will do with separate stand alone controls. On the pool heat exchanger have a blending valve set to the minimum the boiler heat exchanger can have. Say 80C flow and the boiler heat exchanger temp diff is 20C, then set the return to 60C. There is a danger with a pool of having a very large temp diff, so the blending valve puts the heat exchanger into the correct temp diff range. You could have the blending valve set to 40C and the boiler flow temp to 60C. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
#33
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Condensing boiler - odd installation
"IMM" wrote in message ... Ideal ICOS "system" boiler £740.25 Including VAT Ideal ICOS "heating" boiler £675.63 Including VAT Two ICOS condensing boilers at approx 24kW each is about the same price. So may as well get two of them and couple them up. System boilers come with pressure vessel and pump. http://www.discountedheating.co.uk/ Now you have lost me. Two ICOS boilers cost about the same as one Keston when you take into account the extra installation costs not to mention the increased space, flue etc and not being as sophisticated.. mikej |
#34
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Condensing boiler - odd installation
"mike.james" wrote in message ... "Andy Hall" wrote in message Very good point. One I can use in getting them to requote with a better conventional boiler. Which would put the difference between this and a much more efficient condensing model even less. But it would be nice if the gap was narrowed by a price reduction not a price increase. Ah but the flue is there - it isn't a new installation. Don't assume that it would not need to be replaced even for a new CF boiler - it may not be up to spec. The flue is fine and the Mexico is replacing a similar boiler so installation costs are less. I think that you have to make your own decision, but I don't think that your logic is quite correct. There doesn't seem any point to me in replacing ancient technology with new ancient technology when you can have much improved energy usage with a new condensing boiler. I agree but my friend is more interested in money than technology. Andy is on about efficiency, which cascades to money. If you take a look at the Sedbuk site, they indicate that you can easily save £150 per annum on energy in a large house installation when changing from an older boiler of about 65% efficiency. They are about right - I've done it - and that is with with a 25kW boiler. If you factor up to a 40kW boiler, the saving could be £250, although this is for going from a 65% efficient product to a 90% efficient one. For a comparison between a 78% - 80% efficient conventional boiler you would approximately split the difference, so say £100-150 pa..... In my friends world this gives about 5 to 8 years to pay back the invesment. As he is thinking of selling up in at most 5 years you can see that I can't swing the argument on cost - which is all he seems to be interested in. Running a 140,000 btu/h boiler to heat a pool will pay for itself in around 2.5 -3 years. Do some looking and cheaper condensers are had. It appears he wants to pay domestic, and fit domestic, for a commercial setup. Typical small hotel mentality. Just have a shower in those places, and that is why foreigners laugh at our plumbing. At current gas prices, I would be surprised if cost recovery were not achieved in 5 years, and there is no evidence to suggest that gas prices will drop...... This is a better argument, if rising prices could be better :-) mikej --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
#35
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Condensing boiler - odd installation
On Sun, 26 Oct 2003 12:01:28 -0000, "mike.james"
wrote: Now this brings me back to my original point. What does "engineered to take advantage" mean - lower return temperatures? Hence my "silly" idea of putting the pool's heat exchanger in the return flow. mikej I think that you are missing the point. No I'm not if you read my earlier posts you will see that I've agreed that the situation is complicated and I've more or less given up on the idea. All I'm asking for is clarification of what "engineered to take advantage" means in the previous post. Broadly this means installing radiators that are larger and hence have the required output at a lower flow and return temperature, thus improving the efficiency. However..... This is a second order effect after having the condensing boiler in the first place because of the modulating effect of the burner. On days when not much heat is required because the outside temperature is high enough, the radiators in a conventional system will have enough output, even at reduced flow and return temperatures. Therefore, averaged over the year, the boiler will be running quite efficiently anyway. For a condensing boiler, the conventional new system design is to use 70 degree flow and 50 degree return temperatures because most boilers will only modulate down to an output of 10kW or so. At lower implied temperatures the burner would cycle, which reduces efficiency again. If you were to use underfloor heating, there is good marriage with a condensing boiler because it is normally designed to operate at 50 degree flow, 30 return. Depending on the boiler, it may be able to modulate even lower. For example, I just looked on mine (a MAN Micromat) and it is running at close to minimum output. The flow is 45 degrees, return 39 degrees, output 4kW and pump speed 35% with the temperature outside being 9 degrees. There is a steady drip of condensate and no visible outside plume. As you your reply - I follow what you are saying but I don't think the outcome is conclusive because the pool isn't like a room heated by a radiator - it doesn't have to come up to temperature quickly (and it has a much bigger "thermal inertia"). That's true, and thinking about it further, it probably is not a good idea to try to marry up the pool heat exchanger and the house heating anyway. The typical way of working with a condensing boiler when running with radiators and a hot water cylinder is to have either a divertor valve or two zone valves so that the heat is diverted to one or the other. There are good reasons for this - the first being that you normally want to replenish the hot water quickly, and the water has become cold in the cylinder. Therefore, the boiler is switched to it and run at full power, (often at a level above that for the heating) for a relatively short period. Then it is switched back. It also saves having to balance the needs of very different heat loads. Considering the comparison of a pool heat exchanger and a radiator system, these are also very different in thermal inertia, as you say. The pool is going to require a lot of heat for quite a long time, whereas the radiators quite a lot less. Balancing could probably be done, but a more sensible solution is likely to be to have a separate boiler for the pool. Imagine a standard setup (forget the pool for a moment) and the return temperature isn't low enough to get to the dew point i.e. boiler not working at maximum efficiency. There is a common confusion here, also perpetrated by suppliers. The dew point is not a holy grail or thermodynamic orgasm to be achieved at all costs. It simply represents the temperature at which there is a phase change from steam to water vapour or water and latent heat is released. In terms of efficiency when comparing against temperature, there isn't a sudden step, but an increase in the *rate* of efficiency with falling temperature. Now put pool heat exchanger in return flow. Pool water is very cold by comparison with return water flow and should drop its temperature. It might even be enough to make the boiler work at its most efficient. As its in the return it can't alter the efficiency or temperature of the house radiators unless the flow temperature drops. The heat output from the radiators can't be changed by this because the boiler will just work harder to lift the outflow temperature - this must be possible because its how the boiler is designed to work. I.e. if the house radiators were working as required the return temperature would be exactly what we have with the pool heat exchanger in the circuit. The heat output from the radiators will certainly be changed by this because the boiler can only provide a maximum temperature *difference* if cool water is pumped in. For example, if you just had the radiators connected and the boiler operated at full blast it might have a return temperature of 50 and flow of 70 if you have fitted larger radiators. If you now drop the return temperatrure to 30, the flow will not remain at 70, it will drop to 50 and the radiator outputs will be less. Remember that the radiator outputs to the room are proportional to the difference in temperature between the mean value of the radiator temperature ( given by (flow-return)/2 ) and the room air. The point is that the boiler heat exchanger is rated to give 20 degrees temperature lift at full burner output - that's it. At lower outputs it may operate with lower temperature differentials. The only down side is that that pool heat exchanger isn't as efficient because its inflow water is cooler - but who cares? The pools heat cycle is only 4 - 6 hours each day. So just increase it to whatever it takes - 12 hours even. As to what happens when the house CH isn't needed - just switch it back to a flow and return connection as standard. For a modulating boiler I can see that there is the additional problem of the boiler always thinking that the house is cold but then there are room stats for that. This is why connecting in series would create control problems....... mikej ..andy To email, substitute .nospam with .gl |
#36
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Condensing boiler - odd installation
"mike.james" wrote in message ... "IMM" wrote in message ... Ideal ICOS "system" boiler £740.25 Including VAT Ideal ICOS "heating" boiler £675.63 Including VAT Two ICOS condensing boilers at approx 24kW each is about the same price. So may as well get two of them and couple them up. System boilers come with pressure vessel and pump. http://www.discountedheating.co.uk/ Now you have lost me. Two ICOS boilers cost about the same as one Keston when you take into account the extra installation costs not to mention the increased space, flue etc and not being as sophisticated.. mikej Fitting two side by side is not that much in time. The flues come with the boilers. These boilers are "small". He is running a hotel. Having two boilers means backup if one drops out. Bad for business if no hot water or heating. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
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Condensing boiler - odd installation
"mike.james" wrote in message ... "IMM" wrote in message ... What general vote? There is little complexity increase. £800 to £1600. he is being ripped off. Condensing boilers cost little over regular boilers these days. Get another quote. Are you saying pumbworld or similar (checked other online prices) are ripping us off? (See other post for quote) see other post for quote. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/2003 |
#38
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Condensing boiler - odd installation
On Sun, 26 Oct 2003 13:00:20 -0000, "mike.james"
wrote: In my friends world this gives about 5 to 8 years to pay back the invesment. As he is thinking of selling up in at most 5 years you can see that I can't swing the argument on cost - which is all he seems to be interested in. At current gas prices, I would be surprised if cost recovery were not achieved in 5 years, and there is no evidence to suggest that gas prices will drop...... This is a better argument, if rising prices could be better :-) If those are his decision making criteria then fine - I wouldn't waste my time with any more discussion. Another factor that one could consider, since this becomes more of a commercial environment is that in five years, this older type of boiler will be off the market. I would have thought that being able to offer a potential buyer lower running costs at that stage would be an interesting selling point. If I were a buyer, and noticed that an inefficient system had (realtively recently) been installed, I would start to look quite closely at what other capital economies had been made. Presumably a property requiring this size of installation is going to be on the market for a bob or two, so nickel and diming over a couple of hundred quid in capital outlay seems somewhat strange,...... I'd let him get on with it,....... ..andy To email, substitute .nospam with .gl |
#39
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Condensing boiler - odd installation
"IMM" wrote in message ... I agree but my friend is more interested in money than technology. Andy is on about efficiency, which cascades to money. Precisely but you don't seem very consistent when you convert to costs. On the one hand the estimate is 5 to 8 years and you've just quoted 2.5 years without explaining how or why. The reality is that my friend is being offered two boilers one at £800 with an 80% efficiency and £1600 with a 98% efficiency. The first has lower installation costs because it replaces the original boiler so the difference is in fact greater than basic price. In addition the 98% assumes "engineered to take advantage" which as you say means larger rads. This isn't the case so its unlikely the difference will be 20%. Even so the payback time isn't 2.5 years based on his current gas bills it will save £200 (assuming 20% really is achieved) and that means 4 years to recover the extra just in the boiler cost. If the efficiency is less then it will take longer to pay back. mikej |
#40
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Condensing boiler - odd installation
On Sun, 26 Oct 2003 13:12:26 -0000, "IMM" wrote:
Fitting two side by side is not that much in time. The flues come with the boilers. These boilers are "small". He is running a hotel. Having two boilers means backup if one drops out. Bad for business if no hot water or heating. In fact Keston and others make ready to go rigs with two boilers and all the controls and plumbing to do just that..... There is one for the C40 and C55. - ..andy To email, substitute .nospam with .gl |
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