Hello,

Sorry if this is a silly question but why do boilers have two ratings,
e.g. 15-21kW? Is this their output at their lowest setting at output
at their highest setting?

I am looking to buy a new boiler and I can see a couple of potential
models, one is 15-21kW and the other is 15-26kW. If the 15-26 covers
all of the range of the 15-21 and then some, does this mean it is a
better buy as it will give me extra capacity?

Does running a boiler at the low end or high end of its range cause it
to be more or less efficient? I'm sure I remember reading something
about efficiency varying according to load but I can't remember what.

I had a quick read of Ed's boiler choice faq and though it helped with
other questions, I couldn't see the answer to this.

Thanks.

In article ,
Stephen wrote:
Sorry if this is a silly question but why do boilers have two ratings,
e.g. 15-21kW? Is this their output at their lowest setting at output
at their highest setting?

Modern condensing boilers modulate their output to try and keep in
condensing mode - unlike older types which simply switched on and off at
full blast.

I am looking to buy a new boiler and I can see a couple of potential
models, one is 15-21kW and the other is 15-26kW. If the 15-26 covers
all of the range of the 15-21 and then some, does this mean it is a
better buy as it will give me extra capacity?

It would depend on whether your rads could make use of the extra capacity.

--
*Why is "abbreviated" such a long word?

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 29 Aug 2008 10:02:45 +0100, "Dave Plowman (News)"
wrote:

Modern condensing boilers modulate their output to try and keep in
condensing mode - unlike older types which simply switched on and off at
full blast.

Do they condense at low load or when going flat out?

I am looking to buy a new boiler and I can see a couple of potential
models, one is 15-21kW and the other is 15-26kW. If the 15-26 covers
all of the range of the 15-21 and then some, does this mean it is a
better buy as it will give me extra capacity?

It would depend on whether your rads could make use of the extra capacity.

I see. So if I had 19kW of radiators, it would not matter whether I
had a 21 or 26kW boiler. I have added up the rads, though I can't
remember off hand what that came to, but I suppose I need to allow a
bit extra in case I ever fit any more. How much should I add for the
HW (I have a cylinder)?

Thanks.

On Fri, 29 Aug 2008 10:39:27 +0000, Stephen wrote:

On Fri, 29 Aug 2008 10:02:45 +0100, "Dave Plowman (News)"
wrote:

Modern condensing boilers modulate their output to try and keep in
condensing mode - unlike older types which simply switched on and off at
full blast.

Do they condense at low load or when going flat out?

I am looking to buy a new boiler and I can see a couple of potential
models, one is 15-21kW and the other is 15-26kW. If the 15-26 covers
all of the range of the 15-21 and then some, does this mean it is a
better buy as it will give me extra capacity?

It would depend on whether your rads could make use of the extra
capacity.

I see. So if I had 19kW of radiators, it would not matter whether I had
a 21 or 26kW boiler. I have added up the rads, though I can't remember
off hand what that came to, but I suppose I need to allow a bit extra in
case I ever fit any more. How much should I add for the HW (I have a
cylinder)?


The boiler will condense when the return water temperature is cool enough.
In order that the boiler will condense you need to have enough radiators.






--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://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
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

"Stephen" wrote in message
...
Hello,

Sorry if this is a silly question but why do boilers have two ratings,
e.g. 15-21kW? Is this their output at their lowest setting at output
at their highest setting?

I am looking to buy a new boiler and I can see a couple of potential
models, one is 15-21kW and the other is 15-26kW. If the 15-26 covers
all of the range of the 15-21 and then some, does this mean it is a
better buy as it will give me extra capacity?

Does running a boiler at the low end or high end of its range cause it
to be more or less efficient? I'm sure I remember reading something
about efficiency varying according to load but I can't remember what.

I had a quick read of Ed's boiler choice faq and though it helped with
other questions, I couldn't see the answer to this.

Thanks.

Do you just want to replace the boiler? How many bathrooms? Do you have a
tank in the loft? Cylinder? If you have good water mains pressure and flow
a quality high flow modulating combi may be just what you need giving power
shower performance.

In article ,
Doctor Drivel wrote:
Sorry if this is a silly question but why do boilers have two ratings,
e.g. 15-21kW? Is this their output at their lowest setting at output
at their highest setting?

I am looking to buy a new boiler and I can see a couple of potential
models, one is 15-21kW and the other is 15-26kW. If the 15-26 covers
all of the range of the 15-21 and then some, does this mean it is a
better buy as it will give me extra capacity?

Does running a boiler at the low end or high end of its range cause it
to be more or less efficient? I'm sure I remember reading something
about efficiency varying according to load but I can't remember what.

I had a quick read of Ed's boiler choice faq and though it helped with
other questions, I couldn't see the answer to this.

Thanks.

Do you just want to replace the boiler? How many bathrooms? Do you
have a tank in the loft? Cylinder? If you have good water mains
pressure and flow a quality high flow modulating combi may be just what
you need giving power shower performance.

Back to answering a question that wasn't asked, I see.

--
*Give me ambiguity or give me something else.

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
Doctor Drivel wrote:
Sorry if this is a silly question but why do boilers have two ratings,
e.g. 15-21kW? Is this their output at their lowest setting at output
at their highest setting?

I am looking to buy a new boiler and I can see a couple of potential
models, one is 15-21kW and the other is 15-26kW. If the 15-26 covers
all of the range of the 15-21 and then some, does this mean it is a
better buy as it will give me extra capacity?

Does running a boiler at the low end or high end of its range cause it
to be more or less efficient? I'm sure I remember reading something
about efficiency varying according to load but I can't remember what.

I had a quick read of Ed's boiler choice faq and though it helped with
other questions, I couldn't see the answer to this.

Thanks.

Do you just want to replace the boiler? How many bathrooms? Do you
have a tank in the loft? Cylinder? If you have good water mains
pressure and flow a quality high flow modulating combi may be just what
you need giving power shower performance.

Back

Please eff off as you are a total plantpot.

In article ,
Doctor Drivel wrote:
Do you just want to replace the boiler? How many bathrooms? Do you
have a tank in the loft? Cylinder? If you have good water mains
pressure and flow a quality high flow modulating combi may be just
what you need giving power shower performance.

Back to answering a question that wasn't asked, I see.


Please eff off as you are a total plantpot.

QED

--
*Avoid clichés like the plague. (They're old hat.) *

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 29 Aug 2008 15:57:49 +0000 (UTC), Ed Sirett
wrote:

The boiler will condense when the return water temperature is cool enough.
In order that the boiler will condense you need to have enough radiators.

I downloaded the program to calculate heat requirements. I don't know
how accurate the results are because I didn't know what some of the
walls were made of so I made guesses. I wasn't sure what to put in the
heat above and below boxes either. Anyhow, the total heat required
came to just under 15kW for the rads. I don't know whether the
existing rads meet that demand because I don't know their ratings
(they are old single rads with no fins). The 15-21kW boilers seem to
be the smallest I can find, so I guess I will buy one of these.

"Dave Plowman (News)" wrote in message
...
In article ,
Doctor Drivel wrote:
Do you just want to replace the boiler? How many bathrooms? Do you
have a tank in the loft? Cylinder? If you have good water mains
pressure and flow a quality high flow modulating combi may be just
what you need giving power shower performance.

Back to answering a question that wasn't asked, I see.

Please eff off as you are a total plantpot.

Q

Please eff off as you are a total plantpot.

On Sat, 30 Aug 2008 12:22:06 +0000, Stephen wrote:

On Fri, 29 Aug 2008 15:57:49 +0000 (UTC), Ed Sirett
wrote:

The boiler will condense when the return water temperature is cool
enough. In order that the boiler will condense you need to have enough
radiators.

I downloaded the program to calculate heat requirements. I don't know
how accurate the results are because I didn't know what some of the
walls were made of so I made guesses. I wasn't sure what to put in the
heat above and below boxes either. Anyhow, the total heat required came
to just under 15kW for the rads. I don't know whether the existing rads
meet that demand because I don't know their ratings (they are old single
rads with no fins). The 15-21kW boilers seem to be the smallest I can
find, so I guess I will buy one of these.

If you can do so and want to do so, try to replace the existing radiators
with ones with fins. This should allow you to get a slightly better result
from the new boiler.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://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
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

On Fri, 29 Aug 2008 10:39:27 GMT, Stephen
wrote:

On Fri, 29 Aug 2008 10:02:45 +0100, "Dave Plowman (News)"
wrote:

Modern condensing boilers modulate their output to try and keep in
condensing mode - unlike older types which simply switched on and off at
full blast.

Do they condense at low load or when going flat out?

They will condense as long as the water returning to the boiler is
cool enough. IIRC 50-58 degC is the range you are looking for. AFAIK
they will modulate down to try to get the return temperature low
enough.

I am looking to buy a new boiler and I can see a couple of potential
models, one is 15-21kW and the other is 15-26kW. If the 15-26 covers
all of the range of the 15-21 and then some, does this mean it is a
better buy as it will give me extra capacity?

It would depend on whether your rads could make use of the extra capacity.

I see. So if I had 19kW of radiators, it would not matter whether I
had a 21 or 26kW boiler. I have added up the rads, though I can't
remember off hand what that came to, but I suppose I need to allow a
bit extra in case I ever fit any more. How much should I add for the
HW (I have a cylinder)?

Your cylinder should have a power rating for the heat exchanger. If
you have a system where you can heat the central heating and hot water
at the same time then you could add up the total of the radiators and
the hot water coil. Otherwise just take the maximum of the two
figures. Add on a bit incase you swap or add any extra
radiators/change cylinder.

I guess strictly you should size your boiler based on the total heat
loss from your house rather than from the radiators currently fitted.

In most[1] cases the hot water would require a larger amount of power
than the CH.

[1] I'm sure others here will point out many exceptions to this rule.

--
(\__/) M.
(='.'=) Owing to the amount of spam posted via googlegroups and
(")_(") their inaction to the problem. I am blocking most articles
posted from there. If you wish your postings to be seen by
everyone you will need use a different method of posting.
See http://improve-usenet.org

"Mark" wrote in message
news
On Fri, 29 Aug 2008 10:39:27 GMT, Stephen
wrote:

On Fri, 29 Aug 2008 10:02:45 +0100, "Dave Plowman (News)"
wrote:

Modern condensing boilers modulate their output to try and keep in
condensing mode - unlike older types which simply switched on and off at
full blast.

Do they condense at low load or when going flat out?

They will condense as long as the water returning to the boiler is
cool enough. IIRC 50-58 degC is the range you are looking for.

Anything below 58C return water temperature.

AFAIK they will modulate down to try to
get the return temperature low
enough.

Depends on the control system to the boiler. They are not all the same.
Some modulate to maintain the set flow temperature.

Your cylinder should have a power rating for the heat exchanger.

Best a quick recovery coil cylinder. Or fit a bronze pump and plate heat
exchanger and the cylinder will heat in no time and boiler condense all the
same.

"Stephen" wrote in message
news
On Sat, 30 Aug 2008 09:18:30 +0100, "Doctor Drivel"
wrote:

Do you just want to replace the boiler? How many bathrooms? Do you have
a
tank in the loft? Cylinder? If you have good water mains pressure and
flow
a quality high flow modulating combi may be just what you need giving
power
shower performance.

How do you define "good mains pressure"?

Whilst I like the heat only what you need aspect of a combi, which
hopefully saves on the fuel bill, we use economy 7 to heat the
cylinder overnight. We would lose this feature with a combi. I
thought that economy 7 was cheaper than oil for heating water? It also
gives us a back-up system so that if the boiler breaks, we still get
hot water. So I think we would like to stick with a regular boiler
this time.

I am not sure if economy 7 is actually cheaper. If you need backup insert
an instant electric water heater in the combi line - about £100. The DHW
runs though. If the combi is down then turn on the water heater. Gives a get
wet shower and one tap for backup.

You save on standing heat losses with a combi.

In article ,
Doctor Drivel wrote:
Whilst I like the heat only what you need aspect of a combi, which
hopefully saves on the fuel bill, we use economy 7 to heat the
cylinder overnight. We would lose this feature with a combi. I
thought that economy 7 was cheaper than oil for heating water? It also
gives us a back-up system so that if the boiler breaks, we still get
hot water. So I think we would like to stick with a regular boiler
this time.

I am not sure if economy 7 is actually cheaper. If you need backup
insert an instant electric water heater in the combi line - about £100.
The DHW runs though. If the combi is down then turn on the water
heater. Gives a get wet shower and one tap for backup.

And if the combi needs faults seen to that include the water supply to it?

--
*Confession is good for the soul, but bad for your career.

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
Doctor Drivel wrote:
Whilst I like the heat only what you need aspect of a combi, which
hopefully saves on the fuel bill, we use economy 7 to heat the
cylinder overnight. We would lose this feature with a combi. I
thought that economy 7 was cheaper than oil for heating water? It also
gives us a back-up system so that if the boiler breaks, we still get
hot water. So I think we would like to stick with a regular boiler
this time.

I am not sure if economy 7 is actually cheaper. If you need backup
insert an instant electric water heater in the combi line - about £100.
The DHW runs though. If the combi is down then turn on the water
heater. Gives a get wet shower and one tap for backup.

And

Please eff off as you are a total plantpot.

In article ,
Doctor Drivel wrote:

"Dave Plowman (News)" wrote in message
...
In article ,
Doctor Drivel wrote:
Whilst I like the heat only what you need aspect of a combi, which
hopefully saves on the fuel bill, we use economy 7 to heat the
cylinder overnight. We would lose this feature with a combi. I
thought that economy 7 was cheaper than oil for heating water? It
also gives us a back-up system so that if the boiler breaks, we
still get hot water. So I think we would like to stick with a
regular boiler this time.

I am not sure if economy 7 is actually cheaper. If you need backup
insert an instant electric water heater in the combi line - about
£100.
The DHW runs though. If the combi is down then turn on the water
heater. Gives a get wet shower and one tap for backup.

And if the combi needs faults seen to that include the water supply
to it?

Please explain this to me as I'm a total plantpot.

Only a total ****** would suggest a backup system which might not work
when the main one fails and is under repair. Thank god you're not in a
position to specify such things.

--
*A woman drove me to drink and I didn't have the decency to thank her

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
Doctor Drivel wrote:

"Dave Plowman (News)" wrote in message
...
In article ,
Doctor Drivel wrote:
Whilst I like the heat only what you need aspect of a combi, which
hopefully saves on the fuel bill, we use economy 7 to heat the
cylinder overnight. We would lose this feature with a combi. I
thought that economy 7 was cheaper than oil for heating water? It
also gives us a back-up system so that if the boiler breaks, we
still get hot water. So I think we would like to stick with a
regular boiler this time.

I am not sure if economy 7 is actually cheaper. If you need backup
insert an instant electric water heater in the combi line - about
£100.
The DHW runs though. If the combi is down then turn on the water
heater. Gives a get wet shower and one tap for backup.

And if the combi needs faults seen to that include the water supply
to it?

Please eff off as you are a complete plantpot.