Baseboard heaters made by Slant/Fin such as the Fine/Line 30A and BaseLine 2000 produce about 600 BTU's of heat per one foot of baseboard when using 180 degree water. To determine how many feet of baseboard you will need for a particular room, you must determine how many BTU's are required to heat that space. Then, divide this total by 600 to get how many feet of baseboard to install. If you don't end up with an even number, it is always better to get a little more than not enough to be sure that your room will be warm all winter.
Baseboard heaters and Slant Fin Baseboard Heaters can be found at www.supplyhouse.com