Difference in radiator output?

eamon11

hello folks,

I am buying rads for a house and have the btus and sizes made up. I have gotten a few quotes and I cannot understand how 2 rads of exact same size can have such a different heat output?

For example from one builders providers, a quinn rad 500mm x 1500mm double panel,is quoted as having 11349 btu. Another builder provider, with 500mm x 1500mm double panel (dont know make) quotes it as having 7825 btu ! Its the same for all the rads. Surely the heat output is a simple formula where the surface area is multiplied by the water temp, or something to that effect. Is it trickery on the part of some manufactures to obtain higher output values on their rads by adjusting water temp or something? Does anyone know if there really is a difference between the different rads?

Many thanks for your time,


Eamon

Ging Ging

Your best bet is to download the sizing charts from the rad manufacturers website yourself. The builders merchant may be relying on old data for a previous product range.
As for differences between manufacturer and or models of radiator, these may be down to whether the double is a double single convector (fin) or double double convector. They test them under laboratory conditions for set delta degrees between flow and return which may not reflect your set up. One manufacturers "fins" may be larger than another's which would equate to a larger surface area of radiator to emit heat even if both are the same length and height. Things like the paint coating and grade of steel (see big differences in towel rails especially) also allow for differences in heat output.
I prefer Watts to BTUs but even with BTUs you should start with the required heat and find a rad to provide it at a certain flow temp, don't start with a rad size and just pick the biggest output or cheapest purchase cost.

Dardania

Ging Ging covers the it spot on, and just to note from my own experience in sizing rads - the lower your return temperature to the boiler, the better it will condense (e.g. return at 45C is a good idea with modern boilers) and to get that return temp, you need a bigger delta T from the flow temperature (bearing in mind room setpoint) - so be sure of these values for your setup when comparing the rads...

eamon11

you are right. the quinn rads were quoted with a delta 0f 62 and the others delta 50. Big difference.