Say Watt?

To produce a comfortable room temperature of around 70ºF (21ºC): When the outside temperature is at 32ºF (0ºC), you will need about 1kW (kilowatt) of heat for every 494 cubic-feet of space (depending on the number of doors, windows and insulation there are/is in the room, the calculation may vary slightly).

This means that, for example: a room in the region of 24 feet by 20 feet by 8 feet high...will require a heat output of between 7kW and 8kW to adequately heat the 3849 cubic feet of space.

(Okay...got the formula no problem?)