I am commonly asked how big a furnace you need for your home. The answer to this is not as simple as some people think. I will discuss several factors in the sizing of furnaces in detail below. Here's what you should know about picking the right size furnace for your home.
The first is that furnaces are generally sized based on the unit's heat output (BTU).
The bigger the BTUs needed, the larger capacity of the furnace is needed to keep you warm and comfortable all winter long; conversely, a smaller BTU output will make the house warmer with a smaller unit.
In selecting a furnace, this BTU output is usually presented in two ways: the AFUE and the Annual Fuel Utilization Efficiency. The AFUE is a percentage that tells you how efficiently the furnace actually burns fuel to produce heat. For instance, a 90% AFUE would mean that 90% of your fuel is used to heat your home, and 10% is lost up the flue.
To determine the size of furnace you need, you should calculate the total BTU output required by adding together all of the BTUs for each appliance in your house. The easiest way to do this is to add up all of the BTUs listed on the labels of each appliance, then compare them to the BTU outputs of furnace models that you are considering for purchase. You can use the "BTUs To KwH" calculator above to help you determine this.
Next, select a furnace with an AFUE equal to or greater than 90%. This will ensure that at least the maximum possible BTUs reach the house instead of being wasted up the flue or in an inefficient furnace. Furnaces with efficiencies equal to and greater than 93% are readily available and will save additional energy and fuel costs year after year.
It would help if you also consider your climate when selecting a furnace. For instance, if you live in Texas, where winter temperatures only drop into the 40s, you may not need a large furnace as someone who lives in northern Michigan, where temperatures regularly drop below 0. Heat pumps are commonly used to save energy and fuel costs over standard furnaces. They can be up to 30% more efficient than standard units.
Finally, suppose your home is airtight, or the outside temperatures are extreme. In that case, you may want to consider an 80% furnace instead of a 90% unit. This will help ensure that you get the maximum amount of heat output to keep up with conditions.
Check out the best furnace brands to consider before making your decision on a purchase.