Determining the size of your furnace is based on British Thermal Units (BTU), which measures thermal or heat energy. It’s crucial to purchase a typical home furnace that meets you home’s heating needs. Typically, a home furnace produces thousands of BTUs.
It’s important to note that if your furnace is too large, it can very well turn on and off often. If the furnace is too small, it won’t sufficiently heat your home.
Determining the Square Footage
Furnace sizes for homes are calculated in different ways, depending on the contractor. However, there are basic “rule-of-thumb” estimations to help select the proper size for your home. In colder climates, you’ll want a furnace that generates 40 to 45 BTUs per square foot. At this amount, you’ll need 100,000-112,500 BTU furnace to heat a home of 2,500 square feet.
Estimate Furnace Size with Heat Degree Day Calculation
A more accurate way to estimate furnace size is through heat degree day calculation. The calculation for a furnace is: 50 x heating therms X furnace efficiency = loads in BTUs/hour.
Of course, the home is one of the most obvious determining factors for your furnace size. Both small rooms and large rooms actually make a difference. Additionally, the orientation of the home should be inspected such as whether living areas are facing south because they will heat more during the winter.
The home’s construction and insulation is also a factor. For instance, a brick home is more insulated than a house with wood siding. Shrubbery can also decrease the requirements for a large furnace.