Radiators and BTUs

roboffer · 13 Nov 2008 at 18:31

Right then, anyone know much about radiators and their output? Ordered a chrome jobby the other day and it turned up today, seems they might have sent me the wrong item.

The one I ordered was 1200x400mm and had an output of around 2600 BTUs, whereas the one that turned up is 1200x450 with an output of around 2300 BTUs.

Bearing in mind the pictures look pretty much identical, haw can a smaller unit output more heat? Logically thinking I would have thought that the output would be in correlation to its surface area but these fugres would seem to indicate otherwise.

Any thoughts?

Le_Petit_Lapin · 13 Nov 2008 at 18:37

Thats 1/10 the BTU's of a human body, said Morpheus.

So...theoretically, if you were to hire 10 asylum seekers and put them in your room instead, it might work out cheaper in the short run.

Dave · 13 Nov 2008 at 18:49

Heat transfer will depend on three things - heat transfer area, flowrate of heated water and heat transfer coefficient. The coefficient then depends on lots of things, for example the material in the pipe. The smaller radiator could be made of more thermally-conductive materials, or could have a higher flowthrough of water to give it a bigger thermal energy output.

Werewolf · 13 Nov 2008 at 18:52

IIRC it's dependant on the construction of the radiator, newer ones tend to have a lot more fins than older ones, which effectively increase the surface area by a huge amount (look at one that is 15-20 years old and compare it to any of the new ones).

We've been gradually replacing the radiators in our house (25+yo) , and the newer ones put out a lot more heat, even when they are smaller.

Greebo · 13 Nov 2008 at 19:22

Still doesn't make sense though asuming they are both very similar in appearance and both chrome the bigger one should ouput more heat. End of story.

Dave · 13 Nov 2008 at 20:16

Greebo said:
Still doesn't make sense though asuming they are both very similar in appearance and both chrome the bigger one should ouput more heat. End of story.

Yes it does. The fins on the internal parts of the radiator increase the area available for heat transfer, assuming this is the difference between radiators. The size isn't the be-all and end-all of heat output - there could be, for example, greater spacing in between the internal pipes, reducing the heat transfer area. The chrome exterior is also a factor in the heat transfer coefficient, but there's other factors (such as the interior metal used, thickness of pipe etc) that could increase the heat flux through the radiator.