On Mon, 13 Nov 2006 03:00:39 -0800, David Sims wrote:

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
34000-102000 Bthu/h

ecoTEC plus 637 - 12.0 - 37.0kW
40000-126000 Btu/h

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.
--
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
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards