What Size of a Boiler Do I Need for a 1,400-Square-Foot House?

Identification

• Furnace size is measured in British thermal units. The amount of energy consumed by the furnace when it is running is the input Btu, and the efficiency level of the furnace determines its output Btu. When selecting the correct size of furnace for a 1,400-square foot home, you will need to base your choice on the output Btu.

Significance

• Energy Star notes that the most common sizing mistake with respect to heating systems is oversizing. In the case of a boiler, oversizing can result in large temperature swings in the home. An oversized boiler will "short cycle," meaning that it turns off and on too frequently. Conversely, an undersized boiler will run too frequently and may not heat your home adequately during the winter.

Sizing Methods

• You have several ways to calculate the correct boiler size for your 1,400-square-foot home. These include using an online boiler Btu calculator, which asks for information about a home's size, age and location to determine the ideal size. Energy Star notes on its website that when getting a professional estimate, you should make sure the contractor uses Manual J, which is the recommended sizing method in the U.S. Manual J takes multiple factors into account, including the number of windows, construction materials and room sizes.

Considerations

• Energy Star states that many homeowners will simply look at the Btu output of their existing boiler unit when purchasing a replacement. However, Energy Star cautions that this is an unreliable way to calculate boiler size, because there are several other "key factors" to consider. These include the number of occupants in your home and the type of lighting and appliances in your home. If you have a contractor prepare an estimate, Energy Star notes that he should provide you with a written report and warranty after completing his calculations.

Sizes

• While factors such as home size and age will play a part in determining correct boiler size, using a Btu calculator can give you an idea of what size boiler is needed for a 1,400-square-foot home. The size can also vary depending on location. For example, a 40-year-old, 1,400-square-foot home in Philadelphia, Pennsylvania, that uses baseboard heat needs a boiler with 69,300 Btu. By comparison, a home of the same size and age in Charleston, South Carolina, needs a boiler with 53,900 Btu.