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Formulas to calculate the required power output of a radiator for a room of a specific size. Do they exist?

Arran Cameron
Are there any recognised formulas to calculate the required power output of a radiator for a room of a specific size that also takes into account variables such as extra height, large areas of glass, insulation of walls etc? Good quality formulas devised by people who know about thermodynamics as opposed to plumber's rules of thumb passed down from the 1950s.


Numerous online radiator power outlet calculators exist but the formula behind them is not disclosed and the results for the same input variables vary from website to website.
Parents
  • 0
    After running through the calculations a question arises as to how much to overspecify the power output of a radiator.


    For example, the total surface and ventilation losses of a ground floor room is 1240W and 195W are required to raise the air temperature from 5°C to 21°C in one hour. Therefore a radiator with a minimum power of 1435W is required. If a non-thermostatic radiator valve is used then the power output of the radiator should not be significantly higher in order to avoid overheating the room. If a thermostatic radiator valve is used then it provides an opportunity to install a radiator with a considerably higher power output to provide extra heat in the event of a big freeze up when the valve is on a high setting but on an averagely cold day the valve is turned down to shut off the radiator when the room has been heated to its desired temperature.


    Would a 1800W radiator be a realistically sensible choice or overkill?
Reply
  • 0
    After running through the calculations a question arises as to how much to overspecify the power output of a radiator.


    For example, the total surface and ventilation losses of a ground floor room is 1240W and 195W are required to raise the air temperature from 5°C to 21°C in one hour. Therefore a radiator with a minimum power of 1435W is required. If a non-thermostatic radiator valve is used then the power output of the radiator should not be significantly higher in order to avoid overheating the room. If a thermostatic radiator valve is used then it provides an opportunity to install a radiator with a considerably higher power output to provide extra heat in the event of a big freeze up when the valve is on a high setting but on an averagely cold day the valve is turned down to shut off the radiator when the room has been heated to its desired temperature.


    Would a 1800W radiator be a realistically sensible choice or overkill?
Children
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