On Sun, 19 Mar 2017 23:15:33 +0000, John Rumm
wrote:

On 19/03/2017 13:36, wrote:
On 19/03/2017 11:58, Bob Minchin wrote:
wrote:
On 18/03/2017 18:36, wrote:
A while ago I asked about the possible perils of buying a listed house
(17thC timber-framed) - the survey results were so bad that I ran away
bravely. It now seems likely that I'll be buying an unlisted 1930s
"arts
and crafts" style house that seems to be pretty solid (but the
survey is
next week - :eeek!).
This house has a fairly old (20+ years?) Mistral oil-fired boiler,
which
is certain to be non-condensing. I need to check but I think the output
is 160k BTU. My previous boiler experience has all been with gas
boilers.
What do I need to know that I may not know?
What real world efficiency savings am I likely to get by changing it
for
a modern, condensing, boiler?

After a bit of googling I think I can answer my own question. An
efficiency improvement of 25% on 2000 litres/year (no idea whether
that's correct) at 41p/litre is about £205, so that pays back at 15
years. If that's correct, and unless there are any grants, it's worth
keeping the old boiler going for as long as reasonably possible.
Also to reinforce your decision, retro fitting a condensing boiler to
existing rads is not likely to achieve the stated efficiency. To get
even near the published figures, the flow/return temps have to be lower
and so the heat output from the rads will fall.
You will have to up the flow temp and sacrifice efficiency or fit new
bigger rads and allow for that in your capital outlay.

Thanks, that's something I hadn't considered.

Unless the rads were one the small side to start with, I suspect this is
less of an issue in many cases. Most systems are only running part load
for a good part of the heating season, and that is where the condensers
gain...


Yes, but you need a weather comensating controller to do that, if it's
not then the water temperature will stay high, just not on for very
long. An old system isn't likely to have a weather compensating
controller.

When I fitted a condenser here I left most of the rads untouched (apart
from one room that was never really warm enough). My system is weather
compensated, and quite often runs flow temperatures under 50 deg C, and
so gets full condensing efficiency (which ideally needs return temps
under 54 deg c). So there would have been no benefit in larger rads
other than on the very coldest days.

Yes, mines running at 34C at the moment (although the heat's coming
from a thermal store, the boiler was last lit 3 days ago - and doesn't
condense anyway).

On 20/03/2017 09:11, Bill Taylor wrote:
On Sun, 19 Mar 2017 23:15:33 +0000, John Rumm
wrote:

On 19/03/2017 13:36, wrote:
On 19/03/2017 11:58, Bob Minchin wrote:
wrote:
On 18/03/2017 18:36, wrote:
A while ago I asked about the possible perils of buying a listed house
(17thC timber-framed) - the survey results were so bad that I ran away
bravely. It now seems likely that I'll be buying an unlisted 1930s
"arts
and crafts" style house that seems to be pretty solid (but the
survey is
next week - :eeek!).
This house has a fairly old (20+ years?) Mistral oil-fired boiler,
which
is certain to be non-condensing. I need to check but I think the output
is 160k BTU. My previous boiler experience has all been with gas
boilers.
What do I need to know that I may not know?
What real world efficiency savings am I likely to get by changing it
for
a modern, condensing, boiler?

After a bit of googling I think I can answer my own question. An
efficiency improvement of 25% on 2000 litres/year (no idea whether
that's correct) at 41p/litre is about £205, so that pays back at 15
years. If that's correct, and unless there are any grants, it's worth
keeping the old boiler going for as long as reasonably possible.
Also to reinforce your decision, retro fitting a condensing boiler to
existing rads is not likely to achieve the stated efficiency. To get
even near the published figures, the flow/return temps have to be lower
and so the heat output from the rads will fall.
You will have to up the flow temp and sacrifice efficiency or fit new
bigger rads and allow for that in your capital outlay.

Thanks, that's something I hadn't considered.

Unless the rads were one the small side to start with, I suspect this is
less of an issue in many cases. Most systems are only running part load
for a good part of the heating season, and that is where the condensers
gain...


Yes, but you need a weather comensating controller to do that, if it's
not then the water temperature will stay high, just not on for very
long. An old system isn't likely to have a weather compensating
controller.

Without weather compensation it will run at a fixed temperature which
you can control. So if you set the flow temp at something sensible (say
60) then it will likely be plenty high enough most of the time, and
still get full benefit from condensing. You may need to tweak it up on
really cold days.

When I fitted a condenser here I left most of the rads untouched (apart
from one room that was never really warm enough). My system is weather
compensated, and quite often runs flow temperatures under 50 deg C, and
so gets full condensing efficiency (which ideally needs return temps
under 54 deg c). So there would have been no benefit in larger rads
other than on the very coldest days.

Yes, mines running at 34C at the moment (although the heat's coming
from a thermal store, the boiler was last lit 3 days ago - and doesn't
condense anyway).

I just checked ours, its 13 deg outside here at the mo. The boiler is
currently running a flow temp of 41 deg C


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Sun, 19 Mar 2017 15:15:49 +0000, Jeff Layman wrote:

====snip====


Agreed. I saw 2 + 2 = 5 (I should be in politics...)

Or computer programming (2+2=5 #but only for large values of 2). :-)

--
Johnny B Good

On Sun, 19 Mar 2017 18:03:27 -0700, tabbypurr wrote:

====snip====


I passed what I always assumed was a small wind generator today, it was
spinning like a top. Yet only a light breeze... something is not adding
up. I reckon it's a fake, and doesn't generate a thing.

Possibly just a rather ostentatious wind speed sensor to provide a more
accurate assessment of both local wind conditions and the likely visual
impact of the prospective purchase of a small 'domestic class' wind
turbine.

--
Johnny B Good

On 19/03/2017 15:47, wrote:
On Sunday, 19 March 2017 10:36:18 UTC, wrote:
On 19/03/2017 10:12, Fredxxx wrote:
On 18/03/2017 18:36, wrote:
A while ago I asked about the possible perils of buying a listed house
(17thC timber-framed) - the survey results were so bad that I ran away
bravely. It now seems likely that I'll be buying an unlisted 1930s "arts
and crafts" style house that seems to be pretty solid (but the survey is
next week - :eeek!).
This house has a fairly old (20+ years?) Mistral oil-fired boiler, which
is certain to be non-condensing. I need to check but I think the output
is 160k BTU. My previous boiler experience has all been with gas boilers.
What do I need to know that I may not know?
What real world efficiency savings am I likely to get by changing it for
a modern, condensing, boiler?

Personally I would run the system as is for a year to see if it is
adequate and if any other improvements in insulation etc could reduce
the size of boiler required.

Many years ago a 160k BTU boiler would have been a commercial boiler and
it was then cheaper to purchase 2 separate domestic boilers and run in
parallel using non-return valves to prevent unwanted water flows.

That might still be the case, although you would then need 2 flues.

During the discussion I've moved to the same point of view - wait and
see because the break-even is so heavily influenced by the actual oil
consumption. Blindingly obvious with hindsight but it's been useful to
have the discussion.

It would not be cheaper to install two boilers in parallel these days,
even leaving out the maintenance and increased failure risk.

You've not looked on ebay then.

Brings to mind the explanation for why Lindbergh chose a single-engined
aircraft: with a twin there was twice the chance of engine failure and
the remaining engine would not be capable of completing the task.

But the opposite applies with boilers, one running shifts the situation from urgent to not.

And for 50% of the time you might only run with one boiler to prevent
any idling.

I'm not sure what range of modulation you get for oil fired boilers?

On 18/03/2017 20:07, Michael Chare wrote:
On 18/03/2017 19:00, Chris Hogg wrote:
On Sat, 18 Mar 2017 18:36:51 +0000, wrote:

Do they make condensing oil-fired boilers now? AIUI they used not to,
as the benefits in terms of improve efficiency were marginal (oil,
having a composition with less hydrogen and more carbon than gas, per
molecule or per unit weight, doesn't generate as much water vapour
when burnt, so the energy to be recovered by condensing that vapour is
less).

Big old cast iron oil boilers seem to be more reliable than the more
modern ones which seem to be forever having electronics failures if my
neighbours experiences are anything to go by.

I suspect you would find it difficult to buy a domestic non condensing
oil boiler. Are you aware of any?

I think you would also have to get special dispensation to fit one that
wasn't condensing today. Alter it at all and you are supposed to comply
with modern fire safety and bunded oil tank rules too.

--
Regards,
Martin Brown

On 18/03/2017 22:01, NY wrote:
"Michael Chare" wrote in message
news
On 18/03/2017 19:00, Chris Hogg wrote:
On Sat, 18 Mar 2017 18:36:51 +0000, wrote:


Do they make condensing oil-fired boilers now? AIUI they used not to,
as the benefits in terms of improve efficiency were marginal (oil,
having a composition with less hydrogen and more carbon than gas, per
molecule or per unit weight, doesn't generate as much water vapour
when burnt, so the energy to be recovered by condensing that vapour is
less).


I suspect you would find it difficult to buy a domestic non condensing
oil boiler. Are you aware of any?

When we replaced our old Grant oil boiler with a new one (old one's heat
exchanger rusted through) we were told that Grant no longer made a
non-condensing one in the size that we needed. We've been pleased with
the new boiler, though we get more "singing" from the radiators as the
water-plus-Fernox is circulating - and that's with the pump turned to
minimum speed. The increase in noise may be more due to the addition of
Fernox (which may have loosened/dissolved deposits) than the change of
boiler. The boiler itself is quieter (less of a thump when the burner
initially lights up).

This is for an outside boiler, rather than a wall-mounted or
under-worktop one in the kitchen etc.

Interesting. How do you find having an external boiler? How does the
condensate drain avoid freezing when the system is outside?

We may have to go down that route as the position of the old boiler is
not suitable for fitting a replacement (basically it was put in place
and an extension built around it).

No easy way to install a replacement upstairs without either knocking
walls down or dismantling the boiler and reassembling it in situ.


--
Regards,
Martin Brown

On Sunday, 19 March 2017 17:19:28 UTC, Johnny B Good wrote:
On Sun, 19 Mar 2017 00:09:44 +0000, nospam wrote:

On 18/03/2017 18:36, wrote:
A while ago I asked about the possible perils of buying a listed house
(17thC timber-framed) - the survey results were so bad that I ran away
bravely. It now seems likely that I'll be buying an unlisted 1930s
"arts and crafts" style house that seems to be pretty solid (but the
survey is next week - :eeek!).
This house has a fairly old (20+ years?) Mistral oil-fired boiler,
which is certain to be non-condensing. I need to check but I think the
output is 160k BTU. My previous boiler experience has all been with gas
boilers.
What do I need to know that I may not know?
What real world efficiency savings am I likely to get by changing it
for a modern, condensing, boiler?

After a bit of googling I think I can answer my own question. An
efficiency improvement of 25% on 2000 litres/year (no idea whether
that's correct) at 41p/litre is about £205, so that pays back at 15
years. If that's correct, and unless there are any grants, it's worth
keeping the old boiler going for as long as reasonably possible.

It's the absence of such ROI reasoning that allowed the billions of
pounds to be frittered away on solar farms and wind turbines by the
government fulfilling the manifesto promises made purely to win votes
away from the Green Party here in the UK. I guess even the most basic
"Back of a pack of ciggies" long term investment costs analysis were too
much of an "Inconvenient Truth" to be raised as the entirely reasonable
objection to implementing such projects beyond the level of small scale
proof of concept.

--
Johnny B Good

Drivel.
Running cost of renewable energy is very low.
No cost for primary energy.
Low maintenance/attendance costs.
Near zero distribution losses.

On Monday, 20 March 2017 01:03:29 UTC, wrote:
On Sunday, 19 March 2017 17:19:28 UTC, Johnny B Good wrote:
On Sun, 19 Mar 2017 00:09:44 +0000, nospam wrote:
On 18/03/2017 18:36, wrote:
A while ago I asked about the possible perils of buying a listed house
(17thC timber-framed) - the survey results were so bad that I ran away
bravely. It now seems likely that I'll be buying an unlisted 1930s
"arts and crafts" style house that seems to be pretty solid (but the
survey is next week - :eeek!).
This house has a fairly old (20+ years?) Mistral oil-fired boiler,
which is certain to be non-condensing. I need to check but I think the
output is 160k BTU. My previous boiler experience has all been with gas
boilers.
What do I need to know that I may not know?
What real world efficiency savings am I likely to get by changing it
for a modern, condensing, boiler?

After a bit of googling I think I can answer my own question. An
efficiency improvement of 25% on 2000 litres/year (no idea whether
that's correct) at 41p/litre is about £205, so that pays back at 15
years. If that's correct, and unless there are any grants, it's worth
keeping the old boiler going for as long as reasonably possible.

It's the absence of such ROI reasoning that allowed the billions of
pounds to be frittered away on solar farms and wind turbines by the
government fulfilling the manifesto promises made purely to win votes
away from the Green Party here in the UK. I guess even the most basic
"Back of a pack of ciggies" long term investment costs analysis were too
much of an "Inconvenient Truth" to be raised as the entirely reasonable
objection to implementing such projects beyond the level of small scale
proof of concept.

I passed what I always assumed was a small wind generator today, it was spinning like a top. Yet only a light breeze... something is not adding up. I reckon it's a fake, and doesn't generate a thing.


NT

You think that because you're stupid.
Higher up there is more wind. Some times lots more.

On Tuesday, 21 March 2017 00:19:57 UTC, Fredxxx wrote:
On 19/03/2017 15:47, wrote:
On Sunday, 19 March 2017 10:36:18 UTC, wrote:
On 19/03/2017 10:12, Fredxxx wrote:
On 18/03/2017 18:36, wrote:
A while ago I asked about the possible perils of buying a listed house
(17thC timber-framed) - the survey results were so bad that I ran away
bravely. It now seems likely that I'll be buying an unlisted 1930s "arts
and crafts" style house that seems to be pretty solid (but the survey is
next week - :eeek!).
This house has a fairly old (20+ years?) Mistral oil-fired boiler, which
is certain to be non-condensing. I need to check but I think the output
is 160k BTU. My previous boiler experience has all been with gas boilers.
What do I need to know that I may not know?
What real world efficiency savings am I likely to get by changing it for
a modern, condensing, boiler?

Personally I would run the system as is for a year to see if it is
adequate and if any other improvements in insulation etc could reduce
the size of boiler required.

Many years ago a 160k BTU boiler would have been a commercial boiler and
it was then cheaper to purchase 2 separate domestic boilers and run in
parallel using non-return valves to prevent unwanted water flows.

That might still be the case, although you would then need 2 flues.

During the discussion I've moved to the same point of view - wait and
see because the break-even is so heavily influenced by the actual oil
consumption. Blindingly obvious with hindsight but it's been useful to
have the discussion.

It would not be cheaper to install two boilers in parallel these days,
even leaving out the maintenance and increased failure risk.

You've not looked on ebay then.

Brings to mind the explanation for why Lindbergh chose a single-engined
aircraft: with a twin there was twice the chance of engine failure and
the remaining engine would not be capable of completing the task.

But the opposite applies with boilers, one running shifts the situation from urgent to not.

And for 50% of the time you might only run with one boiler to prevent
any idling.

I'm not sure what range of modulation you get for oil fired boilers?

It depends, there are several different principles.
The normal domestic ones zero to not much.

On 19/03/2017 15:47, wrote:
On Sunday, 19 March 2017 10:36:18 UTC, wrote:
On 19/03/2017 10:12, Fredxxx wrote:
On 18/03/2017 18:36, wrote:
.... snipped
This house has a fairly old (20+ years?) Mistral oil-fired boiler, which
is certain to be non-condensing. I need to check but I think the output
is 160k BTU. My previous boiler experience has all been with gas boilers.
What do I need to know that I may not know?
What real world efficiency savings am I likely to get by changing it for
a modern, condensing, boiler?

Personally I would run the system as is for a year to see if it is
adequate and if any other improvements in insulation etc could reduce
the size of boiler required.

Many years ago a 160k BTU boiler would have been a commercial boiler and
it was then cheaper to purchase 2 separate domestic boilers and run in
parallel using non-return valves to prevent unwanted water flows.

That might still be the case, although you would then need 2 flues.

During the discussion I've moved to the same point of view - wait and
see because the break-even is so heavily influenced by the actual oil
consumption. Blindingly obvious with hindsight but it's been useful to
have the discussion.

It would not be cheaper to install two boilers in parallel these days,
even leaving out the maintenance and increased failure risk.

You've not looked on ebay then.
I just did and it hasn't changed my mind. Two smaller boilers are not
cheaper than one larger one and would require twice the maintenance and
(slightly) more complex installation.


Brings to mind the explanation for why Lindbergh chose a single-engined
aircraft: with a twin there was twice the chance of engine failure and
the remaining engine would not be capable of completing the task.

But the opposite applies with boilers, one running shifts the situation from urgent to not.
True, I just thought it was an interesting story ;-)

NT

On 21/03/2017 00:19, Fredxxx wrote:
On 19/03/2017 15:47, wrote:
On Sunday, 19 March 2017 10:36:18 UTC, wrote:
On 19/03/2017 10:12, Fredxxx wrote:
On 18/03/2017 18:36, wrote:
A while ago I asked about the possible perils of buying a listed house
(17thC timber-framed) - the survey results were so bad that I ran away
bravely. It now seems likely that I'll be buying an unlisted 1930s
"arts
and crafts" style house that seems to be pretty solid (but the
survey is
next week - :eeek!).
This house has a fairly old (20+ years?) Mistral oil-fired boiler,
which
is certain to be non-condensing. I need to check but I think the
output
is 160k BTU. My previous boiler experience has all been with gas
boilers.
What do I need to know that I may not know?
What real world efficiency savings am I likely to get by changing
it for
a modern, condensing, boiler?

Personally I would run the system as is for a year to see if it is
adequate and if any other improvements in insulation etc could reduce
the size of boiler required.

Many years ago a 160k BTU boiler would have been a commercial boiler
and
it was then cheaper to purchase 2 separate domestic boilers and run in
parallel using non-return valves to prevent unwanted water flows.

That might still be the case, although you would then need 2 flues.

During the discussion I've moved to the same point of view - wait and
see because the break-even is so heavily influenced by the actual oil
consumption. Blindingly obvious with hindsight but it's been useful to
have the discussion.

It would not be cheaper to install two boilers in parallel these days,
even leaving out the maintenance and increased failure risk.

You've not looked on ebay then.

Brings to mind the explanation for why Lindbergh chose a single-engined
aircraft: with a twin there was twice the chance of engine failure and
the remaining engine would not be capable of completing the task.

But the opposite applies with boilers, one running shifts the
situation from urgent to not.

And for 50% of the time you might only run with one boiler to prevent
any idling.

I'm not sure what range of modulation you get for oil fired boilers?

Some research and sums will be needed, but I wonder whether it would be
better to add a smaller, modern, boiler for periods of light load, and
then to bring-in the existing ancient monster when needed. On face value
that seems quite attractive because it's then easily DIYable, plus it
increases the peak available power.

Hmmm, on further thought, I could use a new boiler to heat the workshop
(one of the first projects) and provide the plumbing so that the output
can be sent to the house as well - I think that's just one NRV, a couple
of lever valves, plus a status light somewhere.
Question: for a certain heat output, is a smaller boiler running
flat-out more efficient than a large boiler running at a lower load and
(probably) cycling?

On 21/03/2017 09:54, wrote:
On 21/03/2017 00:19, Fredxxx wrote:
On 19/03/2017 15:47, wrote:
On Sunday, 19 March 2017 10:36:18 UTC, wrote:
On 19/03/2017 10:12, Fredxxx wrote:
On 18/03/2017 18:36, wrote:
A while ago I asked about the possible perils of buying a listed
house
(17thC timber-framed) - the survey results were so bad that I ran
away
bravely. It now seems likely that I'll be buying an unlisted 1930s
"arts
and crafts" style house that seems to be pretty solid (but the
survey is
next week - :eeek!).
This house has a fairly old (20+ years?) Mistral oil-fired boiler,
which
is certain to be non-condensing. I need to check but I think the
output
is 160k BTU. My previous boiler experience has all been with gas
boilers.
What do I need to know that I may not know?
What real world efficiency savings am I likely to get by changing
it for
a modern, condensing, boiler?

Personally I would run the system as is for a year to see if it is
adequate and if any other improvements in insulation etc could reduce
the size of boiler required.

Many years ago a 160k BTU boiler would have been a commercial boiler
and
it was then cheaper to purchase 2 separate domestic boilers and run in
parallel using non-return valves to prevent unwanted water flows.

That might still be the case, although you would then need 2 flues.

During the discussion I've moved to the same point of view - wait and
see because the break-even is so heavily influenced by the actual oil
consumption. Blindingly obvious with hindsight but it's been useful to
have the discussion.

It would not be cheaper to install two boilers in parallel these days,
even leaving out the maintenance and increased failure risk.

You've not looked on ebay then.

Brings to mind the explanation for why Lindbergh chose a single-engined
aircraft: with a twin there was twice the chance of engine failure and
the remaining engine would not be capable of completing the task.

But the opposite applies with boilers, one running shifts the
situation from urgent to not.

And for 50% of the time you might only run with one boiler to prevent
any idling.

I'm not sure what range of modulation you get for oil fired boilers?

Some research and sums will be needed, but I wonder whether it would be
better to add a smaller, modern, boiler for periods of light load, and
then to bring-in the existing ancient monster when needed. On face value
that seems quite attractive because it's then easily DIYable, plus it
increases the peak available power.

Hmmm, on further thought, I could use a new boiler to heat the workshop
(one of the first projects) and provide the plumbing so that the output
can be sent to the house as well - I think that's just one NRV, a couple
of lever valves, plus a status light somewhere.
Question: for a certain heat output, is a smaller boiler running
flat-out more efficient than a large boiler running at a lower load and
(probably) cycling?

Conventional wisdom was that the smaller fully loaded boiler will be
more efficient. However that assumed non modulating boilers. It also
assumed no pump run on. So each time the boiler cycled, the
(considerable) residual heat in the large lump iron HE would be left to
waft out of the flue.

With a modern boiler it will load match much based on the actual demand
(if it has a decent modulation range - not so true for oil boilers), and
the pump run on should at least dump the residual heat into the heating
system (and newer boilers typically having lighter HEs there is less of
it anyway)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Tuesday, 21 March 2017 08:49:14 UTC, harry wrote:
On Monday, 20 March 2017 01:03:29 UTC, tabby wrote:

I passed what I always assumed was a small wind generator today, it was spinning like a top. Yet only a light breeze... something is not adding up. I reckon it's a fake, and doesn't generate a thing.

You think that because you're stupid.
Higher up there is more wind. Some times lots more.

Stupid, adj.: one who asserts a point of view without bothering to even get the facts.

It was about 2m higher up than I was. It might well experience a little more wind, but not much more.


NT

On Tuesday, 21 March 2017 09:41:38 UTC, wrote:
On 19/03/2017 15:47, tabbypurr wrote:
On Sunday, 19 March 2017 10:36:18 UTC, wrote:

It would not be cheaper to install two boilers in parallel these days,
even leaving out the maintenance and increased failure risk.

You've not looked on ebay then.

I just did and it hasn't changed my mind. Two smaller boilers are not
cheaper than one larger one and would require twice the maintenance and
(slightly) more complex installation.

Strange. Last time I looked there were lots for around £100. Maybe it's the time of year.


NT

On Tuesday, 21 March 2017 09:54:45 UTC, wrote:

Some research and sums will be needed, but I wonder whether it would be
better to add a smaller, modern, boiler for periods of light load, and
then to bring-in the existing ancient monster when needed. On face value
that seems quite attractive because it's then easily DIYable, plus it
increases the peak available power.

Hmmm, on further thought, I could use a new boiler to heat the workshop
(one of the first projects) and provide the plumbing so that the output
can be sent to the house as well - I think that's just one NRV, a couple
of lever valves, plus a status light somewhere.
Question: for a certain heat output, is a smaller boiler running
flat-out more efficient than a large boiler running at a lower load and
(probably) cycling?

It depends on the boilers. Modern wins over historic, greatly so if the old boy is cast iron.


NT

On 21/03/2017 10:15, Huge wrote:
On 2017-03-21, John Rumm wrote:
On 21/03/2017 08:47, harry wrote:

[36 lines snipped]

and here it comes:

Running cost of renewable energy is very low.

So long as you ignore the cost of eliminating the intermittency.

And get large subsidies from the taxpayer.

Or worse, other bill payers...


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 21/03/2017 09:54, wrote:
On 21/03/2017 00:19, Fredxxx wrote:
On 19/03/2017 15:47, wrote:
On Sunday, 19 March 2017 10:36:18 UTC, wrote:
On 19/03/2017 10:12, Fredxxx wrote:
On 18/03/2017 18:36, wrote:
A while ago I asked about the possible perils of buying a listed
house
(17thC timber-framed) - the survey results were so bad that I ran
away
bravely. It now seems likely that I'll be buying an unlisted 1930s
"arts
and crafts" style house that seems to be pretty solid (but the
survey is
next week - :eeek!).
This house has a fairly old (20+ years?) Mistral oil-fired boiler,
which
is certain to be non-condensing. I need to check but I think the
output
is 160k BTU. My previous boiler experience has all been with gas
boilers.
What do I need to know that I may not know?
What real world efficiency savings am I likely to get by changing
it for
a modern, condensing, boiler?

Personally I would run the system as is for a year to see if it is
adequate and if any other improvements in insulation etc could reduce
the size of boiler required.

Many years ago a 160k BTU boiler would have been a commercial boiler
and
it was then cheaper to purchase 2 separate domestic boilers and run in
parallel using non-return valves to prevent unwanted water flows.

That might still be the case, although you would then need 2 flues.

During the discussion I've moved to the same point of view - wait and
see because the break-even is so heavily influenced by the actual oil
consumption. Blindingly obvious with hindsight but it's been useful to
have the discussion.

It would not be cheaper to install two boilers in parallel these days,
even leaving out the maintenance and increased failure risk.

You've not looked on ebay then.

Brings to mind the explanation for why Lindbergh chose a single-engined
aircraft: with a twin there was twice the chance of engine failure and
the remaining engine would not be capable of completing the task.

But the opposite applies with boilers, one running shifts the
situation from urgent to not.

And for 50% of the time you might only run with one boiler to prevent
any idling.

I'm not sure what range of modulation you get for oil fired boilers?

Some research and sums will be needed, but I wonder whether it would be
better to add a smaller, modern, boiler for periods of light load, and
then to bring-in the existing ancient monster when needed. On face value
that seems quite attractive because it's then easily DIYable, plus it
increases the peak available power.

Hmmm, on further thought, I could use a new boiler to heat the workshop
(one of the first projects) and provide the plumbing so that the output
can be sent to the house as well - I think that's just one NRV, a couple
of lever valves, plus a status light somewhere.
Question: for a certain heat output, is a smaller boiler running
flat-out more efficient than a large boiler running at a lower load and
(probably) cycling?

The efficiencies of boiler on full output, reduced/modulated output and
cycling is less obvious that it used to be.

All boilers are now fan flued so there is minimal passage of air within
a boiler when not lit.

That suggests a cycling boiler with a fanned flue is not as bad as an
old boiler where natural convection within a boiler would carry heat away.

I might suggest a boiler running in modulating mode might be most
efficient from a slower flow of hot gases over the heat exchanger
leading to better heat transfer.

Its then not so obvious which is the more efficient, one running at max
or one that is cycling.