1. All electricity going to the heater ends up as heat (it’s not a heat pump here). This all ends up being emitted by the radiator. (losses from pipes would be small, and are ignored)
2. The temperatures displayed are what would happen when the system has stabilised to a ‘steady-state’. (time to reach steady state is relatively short)
3. Values based on an average of manufacturers’ radiator data, but all simple radiators should perform similarly.
4. The surface temperatures across a radiator are never evenly-spread, especially on large radiators, so theory may deviate from practice. The ‘error’ should however be relatively small.
5. Wide low radiators give out a little more head than square or tall ones, but variations are only in the order of 5% or so.