first post, hi i am redoing the living room/dining room and want to put new radiator in and trying to work out the wattage i need in the room 7.10mx3.30mx2.40m there is one radiator at each end of the room under the window, we are mid terrace. i used the b&q calcuator thing and come up with 8924btu so over the 2 radiator 4462 so 1307 watts each radiator, not sure if this is right and if it is, i seen a radiator that is about 200 watts less than i need, will 200watts make much of a difference, would be very greatfully for any help