Radiators, what BTUH?

[MeltingSugs]

I want to change our radiators. They are very good, but not in keeping with the style of the house. I would like to buy column rads, but am desperate not to make the house cold by replacing with ones which have a much lower heat output. No idea what my current ones are.

On google there are lots of websites which will work out the BTUH you need if you enter room and window sizes. Does anyone know if they are accurate, has anyone gone with the estimate and wished they had gone for one with a higher BTUH than suggested? Would I be better to go for the highest BTUH I can afford?

As I understand it you need to consider the size or rather the heating capacity of your boiler.

You can’t just go buying big radiators.

Well you can! But whether the boiler could cope with that much more demand is the problem.

Thanks @tanstaafl that's interesting. We have a bit of a complicated system, and a big thermal store. Maybe I will need someone to come and advise 🤔

If you have a modern radiator, it is very unlikely to have insufficient power.

Are your existing radiators big enough to heat the house sufficiently?

how long does it take to become warm on a cold, frosty morning?

Are your current radiators steel panel? Single or double? What sizes?

how old is the house? Detached? Terraced? How many rooms?

I mean

If you have a modern boiler, it is very unlikely to have insufficient power.

btw

Move into the 1980's and work in kW, not BTU.

Move into the 1980's and work in kW, not BTU.

Unless, of course, the poster happens to be in USA, where they still us imperial measurements, including BTU, for both heating and Aircon

Thank you @PigletJohn

Duly noted about the 21st century! I think our radiators are doubles, will attach a photo. Does the thermal store make any difference, or is it all in the boiler? We have our hot water 'on' constantly as it's meant to be cheaper to keep the tank hot than heat it up from cold. Boiler is a gloworm, I gather they aren't great but it is only two years old.

House is a semi, gets toasty very quickly with the current radiators and they are definitely sufficient. Previous owner was a plumber, so I think he knew what he was doing. It's a cottage from the 1800s so I really don't want to underestimate with the radiators!

Photos of a radiator and the thermal store which I always think looks like a bomb. Still, makes a cracking airing cupboard.

hot water heat usage is not likely to be a problem unless you have a surpisingly underpowered boiler. It isn't true that "it's cheaper to leave it on all day" because that means your boiler will keep heating itself up for short periods, then letting all the heat drain away.

If you have modern double radiators 60mm high they have a nominal output of about 1800W per metre length
example
(it is actually less than that because the calculation relies on some over-optimistic and improbable assumptions)

But you can estimate the nominal output of your old ones and get new ones that are nominally at least equal.

You must have TRVs on all of them except the one in the room where you have your room stat. That way the rooms will not be overheated even if they are oversized. Somewhat oversized rads will heat the room faster from cold, and, once hot, will tick along at low output which gives a more regular and even heat. long, low radiators heat the room more evenly than narrow, high ones.

If not already done, you can have a towel rail that heats up from the thermal store circuit, for example during and after running a bath, if it is adjacent to the airing cupboard. You will need a radiator as well.

p.s.

I see the previous owner was an old-fashioned plumber who didn't believe in insulating pipes, so your airing cupboard is filled with numerous long, narrow, copper radiators to keep it hot even in summer. You're paying for that.