I'm trying to size a Taco circulator for a 119 gal Superstor and having a tough time grasping the btu/hr requirement off my the boiler. Normally I would take the size of the tank and multiply it by 833 (8.33 * 100 delta T) but the Superstor catalog says you need 269,000 btu's for the 119 gallon, based on 180 degree water temp. This is almost 3x as much as the 833 method. Can anyone shed some light?