I am in the process of finishing 2 rooms in my horse barn, 1 as a feed storage room and 1 as a tack room. I am going to install electric baseboard heaters in each room. My question is what size do I go with, 6' or 8'? After much searching of the net there appears to be a formula to determine the size and I can't find it. Room details are below. Room #1 12' x 12' 9 ' drop ceiling with batting above 2 inside walls, 2 outside walls inside walls have R-19 batting, outside walls have 1 1/2" polystyrene 1 door to the outside, 1 door into the barn aisle and 1 window Room #2 12' x 12' 9 ' drop ceiling with batting above 3 inside walls, 1 outside wall inside walls have R-19 batting, outside walls have 1 1/2" polystyrene 1 door into the barn aisle