Working out BTU for old rad.

[aveatry]

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

 

[Agile]

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.

 

[aveatry]

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

 

[lostinthelight]

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?

 

[ianmcd]

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

Great to hear from you my old friend, where do you get the 35% from ?

 

[aveatry]

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

 

[aveatry]

Great to hear from you my old friend, where do you get the 35% from ?

It did seem a tad high to me but not being an expert I did not question it.

 

[diynoob]

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.

Radiator Calculator

Get the right sized radiator for your room. Our calculator with provide heat output recommendations in BTU and Watts.

www.homesupply.co.uk

 

[aveatry]

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.

Radiator Calculator

Get the right sized radiator for your room. Our calculator with provide heat output recommendations in BTU and Watts.

www.homesupply.co.uk

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.

 

[Johntheo5]

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

 

[aveatry]

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%