If you are in the market for a new furnace, you will notice that each unit comes with certain ratings and statistics that describe annual energy usage and efficiency. These numbers are required by the U.S. Department of Energy for each unit so that homeowners can compare the performance of different equipment. These numbers are found on a bright yellow Energy Guide Label on virtually every appliance in the United States. You will notice a Seasonal Energy Efficiency Ratio (SEER) that relates information about how much energy and money a certain unit is expected to use over the course of a year. Additionally, you may also see a different number known as the Annual Fuel Utilization Efficiency (AFUE).

So, what is AFUE in HVAC? The Annual Fuel Utilization Efficiency can be thought of like your car's miles per gallon rating. The mpg for your car tells you how far you can expect your car to travel on one gallon of gas. Similarly, the AFUE is a measurement of how efficiently a furnace converts energy from the fuel it uses to create warm air for your home. A unit with a 90 percent rating means that 90 percent of the unit's fuel produces heat for your home, and 10 percent is wasted. AFUE ratings are a good way to compare efficiencies. The current minimum for new furnaces and boilers is 80 percent AFUE. Let's take a closer look at AFUE ratings.

How are AFUE ratings calculated?

The furnace AFUE rating is calculated using the total annual heating output from the unit versus the amount of fuel input over the same period of time. Since circumstances and situations will vary in each home, the published ratings for equipment are considered the average rating and not the exact efficiency it will achieve each day. Models with higher numbers are usually deluxe heating units with additional features and energy-efficient benefits.

Why does AFUE matter when buying a furnace?

The higher the AFUE rating, the more energy-efficient the furnace will be over time. For homeowners, a heating system with a high AFUE will heat your home faster and could also mean energy savings at the same time. While it is virtually impossible to achieve a 100 percent AFUE rating where no energy is wasted, you can find units with ratings that are close.

To better understand AFUE ratings, consider the efficiency rating as equal to a single dollar. If your system has a 100 percent rating, the entire dollar is spent on home heating, and none is wasted. As the AFUE declines, the remaining part of the dollar is wasted. If the rating is 80 percent, you only spend 80 cents on heating and throw the other 20 cents away. On average, Americans spend $115 each month on energy. An inefficient system could cost you a lot more. In basic terms, a low AFUE rating is likely to cost you more money to heat your home.

What is a good AFUE rating?

AFUE ratings give you an idea of the energy efficiency of furnaces and other heating units. The furnace relies on a fuel source like propane or natural gas to produce heat. The AFUE is an indicator of how well the unit will manage the fuel source to produce heat. Some units will require more fuel than others to deliver warm air to your home. Additionally, AFUE percentages can be lowered by inefficient burners or if heat escapes through a chimney or ductwork.

The Department of Energy classifies a high-efficiency heating system as a unit having a 90 percent AFUE or higher. A mid-efficiency unit will have a rating of 80 to 83 percent. The current standard for all heating equipment is an AFUE of 80 percent. An AFUE is an important factor among others to consider when buying a new furnace. Price, type of system, and fuel source are also important factors.