How does one size a boiler for a house?
To determine the proper size, calculate the heat load served by the boiler by following the procedure explained in the American Society of Heating, Refrigerating, and Air Conditioning Engineers Fundamentals Handbook. Many software products are also available that can guide you through the calculations, and several boiler manufacturers include sizing guidelines or software on their Web sites.
USA Scott has the right answer. It is called a heat loss calculation. You calculate the amount of heat your house will lose, then you install a boiler that will replace that amount of heat. Heat loss is figured one room at a time. Information needed is the size of the room, height of the ceiling, type of wall construction, what R value of insulation, how many and what size doors and windows. This is done for each room, then added up for the whole house.
