The size of a boiler depends on the size of the home and local climate, but a 2,000-square-foot home in an area with a moderate climate could use a boiler rated at 70,000 BTUs, according to BobVila.com. However, choosing the right size requires weighing a number of factors.
Many homeowners and even some contractors install boilers that are too large for a home. The drawbacks of using a boiler that's too small are clear; the home doesn't stay warm enough during cold periods. A boiler that's too large, however, typically only runs for short periods of time. Since short running cycles waste energy, the best efficiency is achieved with boilers carefully sized for particular applications.