What size furnace should you purchase? Do you have a furnace installed in your home that is either too big or too small?
A furnace that is oversized is just as inefficient as one that is too small. An over-sized furnace will incur heat loss due to a condition called rapid-cycling. When this occurs, the furnace starts and stops over and over again. This can cause some areas of your home to be warmer than others. And it will wear out the parts in a much shorter timeframe.
When a professional enters your home to determine the proper size furnace, he or she will use load calculations to calculate the amount of heating and cooling BTUs needed for the entire house. This calculation includes the number of windows and doors, along with the type of insulation used within your home’s walls.
A BTU is a British Thermal Unit, or a measure of thermal or heat energy. BTUs are used to determine thermal energy output from a variety of devices, including your furnace. The energy required to heat one pound of water by one degree Fahrenheit is equal to one BTU. You’ll find a tag with this number in plain view on every new furnace.
While heating contractors use various load calculations to determine furnace size for a home, there are also “rule of thumb” estimates so you can quickly determine a furnace size. For cooler climates like Colorado, a very broad estimate of furnace sizing is to select one that generates 40 to 45 BTUs per square foot. That would mean that for a 2,500 square foot house, you would need a 100,000 to 112,500 BTU furnace to heat it.
The efficiency rating is equally important when selecting a furnace. This rating is called the AFUE or Annual Fuel Utilization Efficiency rating. This measurement is based on the percent of fuel that converts to heat. If a furnace has correct capacity but has poor efficiency will lead to higher costs and possibly need more repairs in the long run due to longer running times to achieve the set temperature.
Modern furnaces have many features, but capacity and efficiency are at the top of the list when selecting the right furnace for your home. A correctly sized furnace will keep your family comfortable for many years to come.