Calculate heat output of existing radiators

theGman

Hi, i'm looking to change the radiators in my house and would like to know if there is anyway to calculate the heat output of the existing radiators. The house has quite large rooms and the radiators seem to be very small, therefore the rooms always feel cold unless the heating is on for extended periods.

chrishutt · Posted: Fri Mar 17, 2006 8:23 pm Post Subject:

Get hold of any radiator catalogue (e.g. via web sites) and find rads of similar size and configuration to your own. The outputs given will be much the same. If you have single or double panels without fins you may not find modern equivalents, but if you reduce output of finned panels by 30% you will have an approximation.

A better approach is to compare the temp. achieved by existing rad to desired temp. in relation to external temp. E.g. outside temp 1C, desired room temp. 21C, actual room temp. 16C, need to increase rad output by 33%. But check also that rads are getting up to temp. - if boiler flow is on max (82C) and return is 70C then average rad temp. should be 76C.

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theGman · Posted: Fri Mar 17, 2006 8:28 pm Post Subject:

Thanks for the fast reply I'm now off to measure all my radiators, why can't I have something else to do on a Friday night?

chrishutt · Posted: Fri Mar 17, 2006 8:31 pm Post Subject:

Note my later edit of previous post.

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JohnD · Posted: Fri Mar 17, 2006 8:50 pm Post Subject:

My unscientific method, with rooms that didn't seem adequately heated, was to replace all the singles with double finned of the same length as I decorated the rooms. You have to put TRVs on of course otherwise you might get overheated, and you can fit new lockshields and drainoffs while you're at it. It's much easier to decorate and paint with the rads off anyway. Spare rooms are turned right down.

I suppose if you had an undersized boiler it wouldn't be the right solution, but I had my cavities filled since the house was built, so it's now plenty big enough.

theGman · Posted: Fri Mar 17, 2006 9:18 pm Post Subject:

An example of my room comparison to size of existing radiator is my 2nd bedroom which is 13' 4" x 9' 7" by @ 10' high and the radiator is only 700mm long. This bed room is always very hard to heat up, it has 2 external walls, another room is 14' 6" x 12' 11" and the radiator is 900mm long. The boiler is a Vokera Excell 80SP, the problem is that it gives me 2 possible max outputs for 2 different inputs, so I don't know wether the boiler is struggling or if there is spare capacity to increase the size of the radiators.

chrishutt · Posted: Fri Mar 17, 2006 9:29 pm Post Subject:

Quote:

The boiler is a Vokera Excell 80SP

That will deliver 24kW output (except when it's doing HW), so you'd need a hell of a lot of rads to overload it!

JohnD's point about oversizing and fitting TRVs is a good one. When you eventually get a condensing boiler oversizing will help it to run in condensing mode and maximum efficiency.

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theGman · Posted: Fri Mar 17, 2006 9:34 pm Post Subject:

I'm also using it for my hot water supply

chrishutt · Posted: Fri Mar 17, 2006 9:39 pm Post Subject:

Do you mean apart from it's Combi function? I'm assuming that it's a combi boiler and that when you're not actually running HW the full output is available to CH. In practice you can assume that most of the 24kW can be available for rads, although you''re unlikely to get near that unless it's a very big house.

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theGman · Posted: Fri Mar 17, 2006 9:44 pm Post Subject:

thanks for all the help now to buy new radiators.