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
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Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html