I'll be purchasing a keystoker boiler very shortly. My house heat load comes to 35,396 BTU's / Hr.(1700 square feet). The mode KAA-2 keystoker boiler has an output of 76,500 BTU's / Hr.. I'm thinking this is the model I need , seeing a boiler should be sized to the heat load. The KAA-2 is the smallest boiler Keystoker makes. The KAA-2 has one 3" x 14" grate. The next size up has three 3" x 14" grates. quite a difference for stepping up one size. My question is; Should I stick with the boiler rated for my heatload? Or , should I buy the next size bigger , and throttle it back?