What is an AFUE rating?

AFUE stands for Annual Fuel Utilization Efficiency, and it is a rating used to measure the efficiency of a furnace, boiler, or other heating appliances that burn fuel. The AFUE rating indicates the percentage of energy from the fuel that is converted into usable heat over the course of a typical heating season.

The AFUE rating is calculated by dividing the heat output of the appliance (in British Thermal Units or BTUs) by the total fuel energy consumed (also in BTUs) during the same period. The result is expressed as a percentage. For example, an AFUE rating of 85% means that 85% of the fuel's energy is converted into heat, while the remaining 15% is lost during combustion or through flue gas.

In the United States, the minimum AFUE rating for newly manufactured residential furnaces and boilers is regulated by the Department of Energy (DOE). The minimum AFUE varies depending on the type of heating appliance and fuel used. As of May 1, 2013, the minimum AFUE rating for gas furnaces ranges from 80% to 98.5%, while for oil-fired furnaces it ranges from 83% to 86%.

A higher AFUE rating indicates a more efficient heating appliance, with less wasted energy and lower operating costs. However, appliances with higher AFUE ratings often come with a higher initial purchase cost. It's important to consider factors such as your climate, heating needs, and fuel costs when selecting a heating appliance with an appropriate AFUE rating.

It's worth noting that AFUE is one of several factors to consider when evaluating the overall efficiency and performance of a heating system. Other factors include the system's size, design, and distribution efficiency. Additionally, AFUE does not account for heat losses through ducts or distribution systems, which can impact the overall efficiency of a heating system.