What size boiler do I need? (UK) | Boiler Size Calculator

[@da_great_mogul]

In the case of system boilers, the more baths and showers you have, the more the boiler will need to reheat the lost water. To ensure that your central heating is not affected, these hot water requirements need to be factored in and you can do this by allowing closer to 9kW and not the 3kW you mentioned.

[@Heatable]

Cheers for your feedback Daniel!

[@foppo100]

20 kw is powerfull enough.To many households have boilers overrated for the system they need.I have 8 radiators and for more than twenty years a small Glowworm system boiler did the job fine keeping our house warm.We have a combi boiler now.I probably will be changing this year for a smaller rating combi boiler.

[@Heatable]

We agree this can happen where boilers are too powerful for what's actually needed. The questions we ask on our website, help us pick a boiler that's a perfect match for you, so you're not paying more for something you don't need. What boiler are you thinking of getting?

[@bigmacntings7451]

It's actually a mixture of both.If you are just paying for the boiler,and not replacing the rads then you lose a lot of efficiency by working the boiler to hard. there was another nice vid on youtube a while back showing why to overspec the rads,not the boiler, that way you will be using the boiler in condesing mode properly. Showers and DHW is a different ballgame and that is extremely variable,depending on the size of your household.This is where it IS useful to overspec especially if you are a landlord or looking to sell a house on.a 25kw DHW might be ok for a young couple to heat and have showers in a 3 or 4 bedroomed house but not much fun with 4 extra kids in tow all covered in muck from work or sports.

[@bigmacntings7451]

I would say as a general rule. flats..go electric. 1 bed/2 bed/small 3 bed house 20kw heat/25k water big 3 bed/4 bed 24kw heat/30k water 5 bed go big. 30kw heat/36kw water.

[@Ky-xu7en]

​@@Heatablepooped myself

[@sobis6670]

Love the out takes 👍😆

[@Heatable]

Cheers Sobi, glad you enjoyed it👍

[@BlueMax333]

I am considering replacing a 30+ year old Potterton Kingfisher RS 50 CAT 1N boiler. The hot water tank iis gravity fed with an overhead tank. Thermostatically controlled power shower require such a tank. OJ Gas & Heating (a WB Accredited installer!) said that he will fit a combi, remove the hot water tank and replace the shower with another type. After watching videos and reading the forums, I am planning to fit a Greenstar 12/15Ri boiler. I can not fathom why a WB Accredited installer recommended fitting a combi

[@farhada147]

Not too sure of the outakes mid video, but the information was helpful, thank you.

[@Heatable]

Thanks for the feedback Farhad, we try to add in outtakes here and there to make what is usually quite a serious subject, more light hearted.

[@waynesworld247]

Nice 👍 best explanation I have seen

[@Heatable]

Thanks Wayne, you're the nicest person we've ever seen.

[@efanutz]

hello mate, i love your videos, great infos you share woth us, i have one quiestion for you! in 5 days it must to decide what combi boilet to buy and install, i live in a apartment, last floor, no roof , only hidro protection, 2 rooms, 47 sqare meters, one bathroom, external insulation 10cm, 3cm insulation on ceiling...19kw viesmann or 20kw vaillant or 24 vaillant boiler...thank you !

[@Heatable]

The smallest combi boiler that you can get is 24kw. However, if you went for a Worcester Bosch 4000 25KW, the heating would modulate down to 3kw so would be very efficient. Head to our website to see the range of boilers that you could have and get a quote in 60 seconds: heatable.co.uk/new-boilers/quote

[@jenniferdavies8910]

Really clear , thank you

[@Heatable]

Thanks Jennifer, don't forget to subscribe to our channel if you haven't already!

[@schmead7257]

We have installed a 45kw Wooster 8000 boiler 19 radiators ranging in sizes across 4 floors the boiler being on the ground floor. It also has a low loss header and 2 zone control. It’s not far of being commissioned Ive just done some research and I’m getting slightly paranoid or just concerned that we have gone over board with spec as I demand the biggest and best. But if we end up just heating one zone I’m afraid it’s going to be counter productive and the system will not perform that well. Any thoughts?

[@Heatable]

Hello, thanks for your comment. A 45kw could be oversized if it is a heat-only boiler. But the boiler will modulate down to the system's demands, to as low as 4.5kw. Providing that the system has been configured correctly, there is no reason why only using 1 zone would cause it to be counterproductive. The boiler can also be 'range rated' to reduce its maximum output based on the size of the system/ heat loss of the property. Hope this helps!

[@twotales7337]

I've got an extended 5 bed. 17 rads, 2 showers, 3 toilets. Currently ran off an old gloworm boiler with cylinder in bathroom. And tank in loft. I'd ideally like a combi to run the hot water and rads for space saving purposes - is this possible?

[@Heatable]

For a house this size with 17 rads, you'll be looking at needing at least a 35kw combi boiler. Combi's typically perform better in smaller homes but there are some powerful options on the market such as the Viessmann 100 - 35kw or Worcester Bosch 8000 - 35kw which should be suitable for your property!

[@twotales7337]

@Heatable thanks so much for getting back to me, and for the info. Someone advised water pressure may be the issue which spooked me?

[@Heatable]

@@twotales7337 Do you know what your water pressure is currently measuring at?

[@ajayPatel-gv2vk]

I only have 12/L cold flow. Will the Viesmann 111 be suitable for my house?

[@Heatable]

Hi Ajay, thanks for your comment. The Viessmann 111 wouldn't be suitable for you, unfortunately, but we'd recommend a smaller combi such as the Viessmann 050 or 100.

[@hardcoreplayafromthehimala4888]

And what is average size\power radiator?

[@normanboyes4983]

I think the approach you take here is far too simplistic, especially in relation to counting up radiators. First off you make no mention of the issue of ensuring the boiler is operating efficiently in the condensing range. The existing radiators may well have been sized to accommodate the much higher flow and return temperatures with non condensing boilers and sizing a condensing boiler to service those emitters continues the sin and the boiler will likely always be out of condensing range. So it is not simple but neither is it too complicated to do some basic calculations on heat losses using web based tools and doing some simple calculations on the existing emitter outputs at a flow temperature of 55C (or even a bit lower if you can) and identifying which ones need upsizing. This exercise will better facilitate specifying boiler size and having an efficient condensing boiler.

[@Heatable]

Thanks for your comment Norman. We gave this calculation as a general rule of thumb, but appreciate there is more depth to it. We'll take this on board for future videos, so make sure you subscribe to stay in the loop.

[@pat589]

Please cut the music.