Plumber says boiler too small for flat/radiators

[Kris Zylek]

Hi All,

I recently purchased a 2 bed flat spread over ground/lower ground floors. Total square footage is about 1300 ft and it has 8 radiators throughout (simple white ones) and a 24kw boiler. Flat seems warm enough with radiators on low / turned off. I had a plumber come around yday to look at potentially replacing the radiators with cast iron / retro ones and he mentioned that the boiler would not be enough to power them. His opinion was that the 24KW boiler is meant for 1 bed flats and its likely working at full power to keep my place warm. And that if i want retro style radiators (steel or cast iron), I'll need to upgrade the boiler to 34Kw.

Searching online, it wasn't that black and white to me that a 24Kw boiler isnt sufficient for a 2 bed flat. Hence looking for opinions from the folks on this forum. Thanks

 

[Londoner2]

My (former 3 bed turned into 5 bed) house heated fine with a 24kw combi boiler.

 

[bernardgreen]

My cottage with two large bedrooms and un-insulated stone walls has been kept warm through out winters by a 16 kW boiler.

If you have a combi boiler then the high power is needed to supply hot water to the taps, it is not needed to keep the flat warm. Get a second opinion.

 

[endaxi]

We had a new boiler installed two years ago. Original boiler was 24kw and all quotes were for a new 24kw boiler which all four installers deemed sufficient. One even measured all seventeen radiators (yes, 17) and said 24kw would be ample. Had new W/Bosch 24Ri fitted and it's worked fine ever since. 4 bed det BTW.

 

[Lower]

My 4 bed, Z shaped house (every room has 3 outside walls), built in the 1920's with solid walls, was heated with a 24KW Glowworm condensing boiler and heated perfectly.

You can do a calc if you know the size of your radiators, but i think your plumber has it wrong.

 

[ianmcd]

Your plumber is talking absolute rubbish 24KW for 8 radiators is way overkill, as has been already mentioned you probably have a combi and the 24KW is for the instant HW , you wont need anywhere near that for your heating

 

[Kris Zylek]

Thank you all so much for your feedback. Will definitely be getting a second opinion. Dodged a bullet there in terms of cost

 

[JohnD]

Have you got a hot-water cylinder or a combi? a combi uses a lot of gas when running a bath or shower.

Consider the possibility that your plumber is an ignorant buffoon.

Heat loss from your flat will depend on the size of the surfaces exposed to the cold (presumably the external walls and the windows, also the roof if you were top floor); the temperature difference between inside and out; and the thermal conductivity of your walls and so on; and draughts or ventilation.

The size of your radiators has no effect on heat loss.

It is quite common to have oversized radiators because they can be run at lower temperaturess leading to greater comfort in the rooms.

If you want to check, go and look up the amount of gas used last winter during the coldest month.

I'll wager your boiler was not running at full power 24 hours a day. It probably used less than 6kw on average.

I also have an 8-24kW boiler. I have a 3-storey detached house. Granted, it is well-insulated and not in the North. During the coldest winter months, is uses an average of 7.2 cubic metres of gas per day. That's about 80kWh per day. Less than 4kW output on average. The houses is heated all day, and to reduced temperatures at night. If you put 24kW or more of heat into your flat, the paint would be melting off the walls.

 

[Harry Bloomfield]

Thank you all so much for your feedback. Will definitely be getting a second opinion. Dodged a bullet there in terms of cost

I agree with others, 18Kw should be more than enough. A larger output boiler will not cost much more to buy, but a smaller one will be more efficient on gas use.

 

[Mottie]

We have a 3 bed semi and an 18Kw boiler. We like it toasty warm but the installer set it to 15kw max as he says that’s more than enough. This is my gas consumption this year so far for heating and hot water - dunno whether that’s good or bad but on the coldest days it’s only around £2 a day.

 

[Harry Bloomfield]

We have a 3 bed semi and an 18Kw boiler. We like it toasty warm but the installer set it to 15kw max as he says that’s more than enough. This is my gas consumption this year so far for heating and hot water - dunno whether that’s good or bad but on the coldest days it’s only around £2 a day.

Something not right with those figures. For instance my figure for January 2019 heating and HW is 138 Kwh. Yours is 2041.65Kwh I think you maybe meant 204.165 ? Mine is a 3bed semi, heated constantly, but at a variable temperature.

 

[flameport]

For instance my figure for January 2019 heating and HW is 138 Kwh.

Impossible.

With gas at say 4p per kWh, that means your gas bill for the whole of January was £6.

 

[Mottie]

Something not right with those figures. For instance my figure for January 2019 heating and HW is 138 Kwh. Yours is 2041.65Kwh I think you maybe meant 204.165 ? Mine is a 3bed semi, heated constantly, but at a variable temperature.

Well here’s January broken down in both £ and KWh.

 

[Harry Bloomfield]

Impossible.

With gas at say 4p per kWh, that means your gas bill for the whole of January was £6.

Whoops, yes caught out by the M3 versus the Kw - It should be x 3.600, so 496.8Kwh x 3.069p = £15.24

There is still something wild about MOTman's figures?

 

[Mottie]

I don’t see how. We pay £100 per month on a standing order and currently we are £253 in credit but we have got the colder months coming!

You paid just £15 for gas heating and hot water for the whole of January? That’s just 50p per day. Were you away on holiday or did you sit covered in blankets and go to bed at 7.00 at night?