Efficiency ratings

AFUE stands for annual fuel utilization efficiency. It measures how much heat actually reaches your house compared with how much fuel the furnace burns. Put another way, it is the share of the fuel's heat that becomes heat for your home instead of being lost.

The numbers have climbed over the years. The first federal furnace standard, passed in 1987 and in force from 1992, set the minimum at 78 AFUE, meaning 78 units of heat out for every 100 units of energy in. Condensing furnaces have AFUE ratings of 90% to 98%. The burning and venting page explains what makes a furnace condensing.

Source: U.S. Department of Energy · ENERGY STAR · U.S. Energy Information Administration

Cooling ratings compare the heat removed with the electricity used. SEER2 is the total heat removed from your home over the cooling season, in Btu, divided by the total electricity used over the same season, in watt-hours. EER2 compares the average rate of cooling delivered with the average rate of electricity used, in Btu per watt-hour. In both, a higher number means more cooling for the same electricity.

You can find these numbers on the equipment's label. The FTC's rule requires makers to attach yellow EnergyGuide labels to many covered products and forbid sellers from removing or changing them. Under ENERGY STAR's rules, a split system's HSPF2 and SEER2 must match the levels reported to the Department of Energy and shown on the EnergyGuide label.

Source: ENERGY STAR · Federal Trade Commission

A heat pump also has a heating rating. HSPF2 is the total heating needed over a heating season in a set test climate region, in Btu, divided by the total electricity the heat pump system uses over that season, in watt-hours. A higher heating rating means more heat for the same electricity. For a heat pump in a cold city, it is the number worth reading closely.

Source: ENERGY STAR

Federal law sets the lowest efficiency that can be sold and installed. Makers have had to meet Department of Energy standards for home central air conditioners and heat pumps since 1992. Any outdoor unit whose certified pairing rates below the standard for a region cannot be installed in that region.

The rules group states into regions. The federal rule's Southeast region lists states such as Alabama, Florida, Georgia, Kentucky, Tennessee, Texas and Virginia, and its Southwest region lists Arizona, California, Nevada and New Mexico; Illinois is in neither. Ask your contractor which standard applies to the unit you are considering.

Source: U.S. Department of Energy · Code of Federal Regulations

ENERGY STAR has its own criteria. For gas furnaces, it asks for 97% AFUE or more in the US North and 95% or more in the US South. Its South list includes states such as Alabama, Arizona, Florida, Georgia, Kentucky, Texas and Virginia, and Illinois is not on it. Certified furnaces must also have 2.0% air leakage or less. ENERGY STAR says a qualified furnace is 15% more efficient than a conventional one.

Heat pumps have their own criteria. ENERGY STAR's key criteria list ducted split heat pumps at 8.1 HSPF2 or more and 15.2 SEER2 or more, and non-ducted split heat pumps at 8.5 HSPF2 or more and 15.2 SEER2 or more. Heat pumps built for peak heating that meet the cold climate criteria may carry the Cold Climate mark. On February 1, 2026, EPA ended the ENERGY STAR specification for central air conditioners. These criteria change from version to version, so check the current ones when you shop.

Source: ENERGY STAR

Chicago needs far more heating than cooling, and that shapes which number matters most. From 1991 to 2020, Chicago's normal year had 5,974 heating degree days and 1,003 cooling degree days. For a home here, the heating rating of a furnace or heat pump deserves a close look, not only the cooling number.

A rating only tells you how well equipment can do. ENERGY STAR says high-efficiency units can save up to 20 percent on heating and cooling costs when installed correctly. Chicago's 2022 energy code is based on the 2021 International Energy Conservation Code with local changes. The sizing page explains why the right size counts as much as the rating.

Source: National Weather Service · ENERGY STAR · City of Chicago