Speccing radiators at the moment.
taking a sample 5.0m x 6.0m bedroom with 2.4m ceiling height. House is very well insulated (new build U=0.27 wall, 0.14 roof etc) gives me a a fabric heat loss of about 140W/h. Now, Im planning on a whole house heat recovery system, so if assume one air change an hour but 75%+ heat recovery implies something like 320*25% vent loss i.e. about 80W/h. So a total requirement of say 220W/h or 6,500 btu.
That's a 1200mm x 600mm aluminium radiator which seems about normal.
If I didnt have the heat recovery system or decent U-values that quickly gets to 19,000 btu or a 3600mm x 600mm radiator!??! 
can that be right?
