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

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

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

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?

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

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.

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

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:-

In the BoilerChoice FAQ (the one that's sometimes referred to as a museum
piece)

Only by one person. Others think it is very useful and glad it is
there.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

David Sims wrote:

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

That should read 34.37KwH (i left number of floors on 1 - it should be
2!)

David Sims wrote:
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

I think you mean 20KW.

David Sims wrote:
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

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.

I used the term downsize because I was thinking a new boiler would be
more efficient

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.

Ian Stirling wrote:

David Sims wrote:
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

Are you sure about this?

I am not having a good day

You are correct to be sceptical the correct figure is about 400 sqm

On Tue, 14 Nov 2006 05:44:23 -0800, David Sims wrote:

Ian Stirling wrote:

David Sims wrote:
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

Are you sure about this?

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.

--
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