Working out BTU for old rad.

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I have an old rad in a bedroom that is 480wide x 590 single with no fins that I want to swap for a larger one as this has never been enough. I am trying to work out what its BTU/W is now as a base guide to getting something warmer.
As a rough guide I am looking at its surface area and using a stelrad equivalent serface area rad spec to give me the BTU / W of my old one but the only problem is the stelrads have fins -- would this make much difference in the BTU/W.

I cannot just whack a bigger one on with a stat as the pipe work wont allow for a double rad distance from the wall so am stuck with a single panel with fin option.
I can get away with a 500 wide one to replace my 480 wide one as it has a little drain screw cap extra piece on the tail making the whole thing wider so my pipe work should accommodate a new 500wide rad.
Thanks
 
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You can work out heat outputs using makers data.

Typically fins add about 35% to the heat output of a single panel.

Usually you can extend feed pipes outwards to allow a wider radiator.
 
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Thanks but the rad I am replacing is an older one of unknown make.
Its a bedroom rad and hoping to just turn off the bathroom and other bedroom rad upstairs- drain this rad and be able to swap valves. As upstairs and other rads shut both sides there should not be much more than the rad its self to drain ? -- Combi Boiler. Problem is when trying to solder a fitting with water in the pipe- even a few inches lower than the cut end. So don't fancy extending the pipe. A new 500w rad should do but just trying to work out how high I should go.
Those fins add quite a lot then at 35% .
So I recon my 480x580 finless rad to be about 1000 BTU then
 
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If your going to the trouble of fitting a new rad ,why not work out the heat requirement for the room and see what size the rad is for the recommended output?
 
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lostinthelight​

That could be the way to do it. But just wanted something hotter but wanted to know how much hotter then the old hotness :)
 
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The old radiator output is irrelevant and doesn't help determine what you need. Just use a radiator calculator and oversize it a bit if you are using a TRV.

 
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The old radiator output is irrelevant and doesn't help determine what you need. Just use a radiator calculator and oversize it a bit if you are using a TRV.

Yes ultimately that is the way to go but I would still like to find out what the old un-finned one was giving out.
 
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Thanks but the rad I am replacing is an older one of unknown make.
Its a bedroom rad and hoping to just turn off the bathroom and other bedroom rad upstairs- drain this rad and be able to swap valves. As upstairs and other rads shut both sides there should not be much more than the rad its self to drain ? -- Combi Boiler. Problem is when trying to solder a fitting with water in the pipe- even a few inches lower than the cut end. So don't fancy extending the pipe. A new 500w rad should do but just trying to work out how high I should go.
Those fins add quite a lot then at 35% .
So I recon my 480x580 finless rad to be about 1000 BTU then.

I have a 45 year old 2134X475mm nonfinned single that I have recorded as 4500BTU so yours might be ~ (480*580)/(2134*475)*4500 or 1235BTU

That was a "60deg" rad so at "50deg" your rad output would be (50/60)^1.3 X 1235 or 974BTU
 
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I have a 45 year old 2134X475mm nonfinned single that I have recorded as 4500BTU so yours might be ~ (480*580)/(2134*475)*4500 or 1235BTU

That was a "60deg" rad so at "50deg" your rad output would be (50/60)^1.3 X 1235 or 974BTU
that is really helpful thank you for doing all the maths.
looking at the specs for a new single convector stelrad 450x600 -which is the nearest size I can find to my original one the figures for that are 1548 BTu.
Based on that size and your estimate of 1235 I recon the addition of fins increases the BTu by 25%
 

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