What Is The Correct Way To Size A Boiler?

The correct way would be to do a heat loss calculation using an IBR guidebook. Your region has alot to do with the sizing. some methods are to use square footage but this often results in an undersized boiler. Each foot of baseboard is equivalent to 600 btu's. To give you an idea, i have an oversized cape.44' x 28" my boiler is 107,000btu's. Not too small and not too big. Heats this place great and is efficient. With the heat loss you figure out what you need in each room and that'll give you your boiler load. Just plug in the numbers on the sheet and use the guidebook to find the numbers to plug in. Easier than it sounds. If you go too big, the boiler will short cycle and cost you in fuel, too small and it'll run constantly to keep up and will definitely bankrupt you in fuel cost especially if you have oil. Good luck. You can get these guidebooks at most supply houses. Or they can tell you where to get them.