Boiler Replacement - flow and return pipes

[kevski]

I have an Ideal WLX RS60 boiler I want to replace. I have had four quotes for replacement boilers which include a British Gas 330+ High Efficiency Boiler, a Vaillant EcoTEC Plus 630 System Boiler, a 24Kw Baxi boiler and a 18Kw Glow Worm Boiler.

Two of the quotes said the 22mm flow and return pipes need replacing with 28mm and two of the quotes said the existing 22mm could be used. I'm confused on whether the 22mm flow and return pipes need to be replaced, can somebody advise me.

I live in a 1930's 4 bedroom semi with 12 radiators.

Regards
Kevski.

 

[Agile]

You have more of a problem with an oversized boiler than the pipe sizes!

An 18 kW or a 30 kW should send alarm bells ringing!

You need to do a whole house heat loss calculation to see what boiler power is needed.

To compare that with the output of the existing rads you could tot them up and see what their combined output is.

I would expect the 18 kW is quite adequate!

Ask the 30 kW guy why that size!

Tony

 

[D_Hailsham]

You need to do a whole house heat loss calculation to see what boiler power is needed.

Use this: Boiler Size Calculator

To compare that with the output of the existing rads you could tot them up and see what their combined output is.

Use this: Stelrad Elite Catalogue

It does not matter if the rads add up to more than the boiler calculator. It just means you can run your boiler at lower temperatures.

 

[kevski]

I did a calculation of the boiler size required and it came out at 25Kw, based on that do I need 28mm for the flow and return pipes.

Thanks for D_Hailsham and Agile's help.

Regards
Kevski

 

[D_Hailsham]

I did a calculation of the boiler size required and it came out at 25Kw, based on that do I need 28mm for the flow and return pipes.

22mm should be OK; it all depends on your radiators. Did you do the rad output calculation I suggested? If so, what was the total rad output?

 

[kevski]

D_Hailsham - by my calculations the rad output is 13475 Watts and 45973 Btu/Hr.

Kevski

 

[D_Hailsham]

D_Hailsham - by my calculations the rad output is 13475 Watts and 45973 Btu/Hr.

You need a 25kW boiler but only have 14kW of rads? You will get cold!

The other possibility is that you have made a mistake.

24kW does sound a lot - unless you have a large old house with non-existent insulation. Could you post the info that you put into the Boiler calculator so I can check it?

 

[kevski]

D_Hailsham - Here's the info as requested, I measured the house again and adjusted the amount of insulation and came up with a boiler size of 16.58Kw which is closer to the rad output which I recalulated to 14.84Kw :-

Based on this I assume I only need an 18Kw boiler, I would like to add at least one radiator in the future so would it be prudent to install a 24Kw boiler. Whether it's 18Kw or 24Kw is it okay to use the existing 22mm flow and return pipes rather than replace them with 28mm as recommended by a couple of the plumbers I have had quotes from.

BOILER SIZE CALCULATION
The WHOLE HOUSE BOILER SIZING METHOD on-line
calculator has used the following parameters:-
The dwelling type is semi-detached approx 9metre x 9metre with double glazed windows with metal frames.
The external walls are cavity, no insulation.
The roof is pitched with 50 to 75mm of insulation.
The Dwelling is in the south east or Wales.
The following three major contributors to the heat requirement
are all affected by the levels of insulation.
The WINDOW heat loss is 3.18 kW
The WALL heat loss is 4.85 kW
The ROOF heat loss is 2.17 kW
Note down the kW readings (or print this page) then press your
browser's Back button.

If better insulation is possible, make selections with higher levels of insulation,
then calculate again to see the effect on the boiler size required.

By spending money on, say, more loft insulation you may save money on the
price of the boiler, and you will definitely save money FOREVER on your heating bills.
The required boiler output is 16.58 kW

Regards
Kevski

 

[ianniann]

Spend 200 quid on cavity wall insulation, top up your loft, and buy the smaller boiler

 

[D_Hailsham]

The WINDOW heat loss is 3.18 kW

Changing to UPVC would be expensive!

The WALL heat loss is 4.85 kW

Cavity Insulation would reduce this to 1.26kW

The ROOF heat loss is 2.17 kW

Adding extra insulation to make it 250mm would reduce this to 1kW

This would then give a boiler size of 11.32kW.

You can get very good deals on cavity and loft insulation, including free in some cases. Check out Energy Savings Trust Grant Search

The 11.32kW boiler size includes 2kW for the hot water cylinder. so your heating requirement is 9.32kW. You say that you have 14.84kW of rads, which means you have sufficient rad capacity to heat your house when it is -13C outside!

I would install a 15kW boiler with weather compensation. The Remeha 15V would be ideal.

If you want a system boiler, the smallest Remeha is the 18S; but this can be set to give a max output of 15kW.