Boiler size

katyacanim

Hi, I've just had a quote for new LPG central heating installation in a 3 bedroom bungalow. I was given a 35 kw boiler.
I was wondering, maybe it's too big for my house, does more kw boiler consume more gas for the same amount of heating?

matelodave

Is that for a combi boiler (note combi and condensing are not the same). 35kw sounds about right for a combi as it should give you a reasonable flow of hot water, A combi heats the hot hot water as it flows through it, rather than storing it in a tank, so you need a lot of kw to give you a reasonable flow, especially in the winter. Have you got more than one bathroom?. A smaller boiler may not give an adequate flow.

For heating it will only produce as much heat as your house requires

If you are getting a system boiler - you will also have a water tank - then it sounds a bit on the big side.

Cardew

I assume this is not a combi boiler i.e. you have a Hot Water tank?

The estimate should have taken into account the size of your property, and importantly the standard of insulation, before selecting the size of the boiler.

With condensing boilers for maximum efficiency the boiler should not be over-sized.

Perhaps you should get another quote?

katyacanim

Thank you for reply.

It is a combi boiler with 11 radiators

teddysmum

Some manufacturers (certainly WB) have a calculator, on their website,which recommends the boiler size for your circumstances.


I checked out of curiosity, when one person quoted me a lower price, but for a smaller boiler, than others had. It turned out that the smaller boiler would have been ok, but would not cope with something like the use of kitchen taps at the same time as bathroom ones. (This was for mans gas,though.)

Cardew

katyacanim wrote: »

Thank you for reply.

It is a combi boiler with 11 radiators

With a combi, the production of Hot water for taps etc determines the output of the boiler; the higher the value the greater the Hot water flow.

The 11 radiators would not normally need anything like 35kW

System

katyacanim wrote: »

Hi, I've just had a quote for new LPG central heating installation in a 3 bedroom bungalow. I was given a 35 kw boiler.
I was wondering, maybe it's too big for my house, does more kw boiler consume more gas for the same amount of heating?

Cardew is spot on. I am having a new system boiler installed in my house next month. As a starter for '10', the installer measured the house and checked cylinder size, bath outlets and he tested water flow. He concluded that heating alone (5bed house) required a 18kW boiler but HW heating required slightly more. (It would still re-heat with an 18kW boiler but it would take a lot of time). His recommendation was that I should go with a 24kW boiler.

Another installer took 5 minutes to walk around the house and came back with a quote for a 35kW boiler.

My advice: take your time and get as many quotes as you can.

sk240

I had a 32KW vaillant combi installed a few years ago, and i too live in a three bed house.
In hindsight i could have gotten away with a 24kw, as my boiler never goes above 50% output, and i suspect your in the same situtaion.

EnglishMohican

If you have a combi boiler already (so that is what your house is plumbed for) or you positively want a combi boiler then 35kW may be reasonable.

If you have a hot water tank and a system boiler already and are happy with that then something much less will do. I have a 4 bedroom house and a 12kW condensing boiler. As it happens, my radiators and piping will not spread even as much as 12kW around the house so anything more than 12kW is a total waste. Similarly, the pipe that brings water to my house is too small to supply water fast enough for a big combi to heat when filling a bath.

Yet a supposedly reputable local heating engineer/plumber recommended a 32kW combi boiler. Maybe he had one going spare!!!!!

None of the "heating engineers" who quoted for me did a careful assessment of the existing radiators or the water flow into the house. Be careful accepting the combi solution unless you are really sure it is right for your house.