Currently:
Large 4 bed house 2 baths, 2 showers
Tanked hot water with Y plan heating (and now a thermostat !)
Ideal Mexico RS125 65% efficiency 37KW depending on burner setting which is either 15.5 or 10.5 mbar 1000000 or 125000 Btu/h
If we replace it with a Vaillant can we downsize
e.g.
ecoTEC plus 630 - 10.0 - 30.0kW
ecoTEC plus 637 - 12.0 - 37.0kW
This one isn't actually downsizing, it automatically varies the power between 12 and 37Kw.
How often do you take two showers (as the household, presumably you don't yourself) at once?
Is the property insulated? Walls, floor, ceiling? About what is the external wall area? As a rough guide, what's your heating bill over the year?
Do you want to downsize as the new one is cheaper?
The 30kW will be fine provided you don't have a leaky listed property.
If it isn't fine, you should spend any additional money on insulation rather than a bigger boiler anyway.
Christian.
In the BoilerChoice FAQ (the one that's sometimes referred to as a museum piece) you'll find a link to a Boiler Size calculator.
For this application you'll only need to consider the space heating load.
If you do the sums, add 10%, (Ed's illegal [1] but sensible fiddle factor to make sure we don't end up with tears), then choose a model with the required power.
Also note that older boilers often quote outputs to the water and gas inputs and these are very different from each other. So the output to the water is what counts.
[1] Because it (slightly) contravenes Part-L of the building regs.Ok thanks for the replies (too much to quote)
House has solid walls, good insulation in loft >200mm
The external walls measure roughly 1000 sqm
I used the term downsize because I was thinking a new boiler would be more efficient
The boiler calculator gives 20.4 KWH
On Mon, 13 Nov 2006 18:42:39 +0000 (UTC) someone who may be Ed Sirett wrote this:-
Only by one person. Others think it is very useful and glad it is there.
That should read 34.37KwH (i left number of floors on 1 - it should be
2!)
I think you mean 20KW.
Are you sure about this?
Assuming 2 storys, this is about 200m of wall, or 3600m^2 of floor area, if one side is a quarter of the length of the other and it's rectangular.
This may not actually be the case.
A larger boiler - for a condensing boiler running at a low output temperature, may actually be slightly more efficient - more of the output steam in the output can be condensed, as it has a larger heat exchanger - sized for the maximum output. This means that at lower output, the exhaust gasses get closer to the water temperature.
However, larger boilers may use greater amounts of electricity, and it doesn't take much of this to knock off any potential savings.
Yes, but that means you have less gas input for the given heat output, not that you reduce the heat output.
Of course, if some naughty manufacturer/retailer is describing their boilers by gas input...
Owain
I am not having a good day
You are correct to be sceptical the correct figure is about 400 sqm
Once you have the required output then you can make a sensible choice. Getting the starting data correct is useful.
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