Does any know how to calculate the ize per room. Say 12x14 ft. Thanks

Rule of thumb is 10 watts per sq foot of floor area, based on an 8 foot ceiling height. 12 x 14 room is 168 sq ft, so that would be 1.68 kw. one foot of baseboard heat is typically 250 watts, so that would be 6.72 feet (have to round up of course) of baseboard heat required.

Thanks i have only replaced existing nerver install new.