AFUE, SEER2 and HSPF2: HVAC efficiency ratings explained

Updated November 10, 2026 · KeystoneProGuide editorial team

What do HVAC efficiency ratings tell you?

How much heating or cooling a unit delivers for the fuel or electricity it uses, measured under standard test conditions. They let you compare two models on paper. They do not tell you how a system will perform in your house, which depends on sizing and installation. ENERGY STAR says improper installation can reduce efficiency by up to 30 percent.

What is AFUE?

Annual Fuel Utilization Efficiency, the rating for furnaces and boilers. ENERGY STAR defines it, in general terms, as the percentage of the heat in the incoming fuel that becomes heat for the house instead of being lost. A 97 percent AFUE furnace turns 97 percent of the fuel's energy into heat for the home, by that test.

The ENERGY STAR levels that apply to a Pennsylvania home:

ENERGY STAR also requires certified furnaces to leak no more than 2.0 percent of their airflow through the cabinet, and says they have more efficient blower motors than standard models. For boilers, it says the gas threshold is about 6 percent above the federal standard and the oil threshold about 1 percent above it.

What are SEER2, EER2 and HSPF2?

The ratings for air conditioners and heat pumps. ENERGY STAR's definitions, from its heat pump criteria:

• SEER2 is the total heat removed from the home over the cooling season divided by the electricity used in that season. It is the seasonal cooling rating.
• EER2 is the cooling delivered at a steady rate divided by the electricity used at that rate. It is a single-rate measure rather than a seasonal one.
• HSPF2 is the total heating delivered over the heating season divided by the electricity used. It is the seasonal heating rating, and the one to look at closely for a heat pump that will heat a Pennsylvania house.
• COP, the coefficient of performance, is heat delivered divided by electricity used under one set of conditions.

The "2" shows the rating was measured under the federal test procedure in Appendix M1; the criteria page says the same measures under Appendix M are written without it (SEER, EER, HSPF). Compare SEER2 with SEER2, not with a SEER figure.

What levels does ENERGY STAR set for heat pumps?

For a split-system heat pump, one with separate indoor and outdoor assemblies connected by refrigerant piping, certification requires at least 15.2 SEER2, 11.0 EER2 and 7.8 HSPF2. Single-package units, with everything in one cabinet, need at least 15.2 SEER2, 10.0 EER2 and 7.2 HSPF2.

The cold-climate label goes further on heating: at least 8.1 HSPF2 for ducted split systems and 8.5 HSPF2 for ductless ones, plus a COP of at least 1.75 at 5°F and at least 70 percent of rated heating capacity at that temperature. ENERGY STAR recommends a cold-climate model where winters regularly drop below freezing.

How much difference does a higher rating make?

ENERGY STAR gives savings for its certified equipment against standard models:

• certified gas furnaces in the northern states: up to 18 percent more efficient than baseline, saving $160 a year;
• certified oil furnaces: up to 4 percent more efficient, about $90 a year;
• certified gas boilers: about $780 over the product's life; oil boilers $200.

For heat pumps, ENERGY STAR says a certified air-source unit can deliver up to three times more heat energy than the electricity it consumes. Higher ratings cost more: Angi's cost survey, for example, prices heat pumps rated 14 SEER at $1,600 to $4,900 for the unit and 20 SEER at $3,600 to $9,500, before installation.

How should you use ratings in a quote?

1. Get the model numbers of every component. ENERGY STAR says the proposal should list them. A heat pump's rating applies to a matched outdoor and indoor combination, so both numbers matter.
2. Ask for the ratings in writing and whether the combination is ENERGY STAR certified.
3. Ask the contractor to show the savings. ENERGY STAR says contractors should be able to show you calculations of savings for certified equipment.
4. Compare like with like. A quote for a 97 percent furnace and a quote for a lower-rated one are not the same product, and ENERGY STAR warns that the lowest price may not be the best deal if your energy costs will be higher.
5. Do not let the rating replace the installation checks. Sizing, airflow, refrigerant charge and duct leakage, all on ENERGY STAR's quality-installation list, decide whether you get the rated efficiency.

Does the thermostat matter to efficiency?

It can. ENERGY STAR says that for the very highest-efficiency equipment, such as an air conditioner rated 20 SEER or higher, you may want a controller from the same company, and that any smart thermostat must be compatible with the system.

National prices for each type of equipment are in the cost guide, and the case for replacing an older unit is in repair or replace. Contractors are listed on the HVAC contractors directory page.

Sources

1. Furnaces Key Product Criteria, ENERGY STAR
2. Furnaces, ENERGY STAR
3. Boilers, ENERGY STAR
4. Heat Pump Equipment Key Product Criteria, ENERGY STAR
5. Air-Source Heat Pumps, ENERGY STAR
6. Smart Thermostats, ENERGY STAR
7. 10 Tips for Hiring a Heating and Cooling Contractor, ENERGY STAR
8. Heat & Cool Efficiently, ENERGY STAR
9. HVAC Quality Installation, ENERGY STAR
10. How Much Does a Heat Pump Cost? [2026 Data], Angi