Q: What is the difference between SEER, HSPF, and COP, and what should we be looking for when recommending heat pumps for whole-house heating and cooling? All the equipment installed on our jobs recently lists SEER2. What does this mean? Is it different from SEER?

A: Connor Dillon, quality manager at the Building Science Institute, a firm offering training and quality control to home energy raters, responds: SEER, HSPF, and COP are three efficiency units used with HVAC equipment like air conditioners, air-source heat pumps, and ground-source (or geothermal) heat pumps. SEER represents the cooling efficiency of air conditioners and air-source heat pumps. HSPF represents the heating efficiency of air-source heat pumps, while COP is typically used for ground-source heat pumps in heating mode.

When you’re assessing heat pumps to be installed, you need to know that the higher the number, the more efficient the system is. A 15 SEER, 9 HSPF air-source heat pump will perform better than a similarly sized system with 14 SEER and 8 HSPF. And all manufacturers are required to meet minimum efficiencies set for equipment by the federal government. This creates the “floor” of efficiency for HVAC equipment. And speaking of the federal government ...

When assessing heat pumps to be installed, you need to know that the higher the number, the more efficient the system is. This holds true whether it’s SEER, HSPF, or COP.

At the beginning of 2023, two important updates were made by the Department of Energy:

First, the federal minimum efficiencies for split-system air conditioners and heat pumps were increased for the first time since 2015. The ratings vary by region, but broadly speaking, they were raised by 1 SEER and roughly 0.6 HSPF for all regions.

Second, the calculations for the efficiency units like SEER and HSPF were modified. This created a “new” unit of measurement, represented as SEER2 and HSPF2—COP was not affected by the new calculations. So the “old” SEER and HSPF calculations are now called SEER1 and HSPF1, respectively.

These new calculations typically lowered the number (but not relative efficiency) of HVAC equipment. Most 14 SEER1 systems are now calculated as 13.4 SEER2, for example. As you can imagine, this caused some confusion—in appearance, “lowering” the efficiency of a piece of equipment while simultaneously requiring that same system meet a higher minimum.

However, most manufacturers are now producing systems using the new efficiency calculation, while meeting the higher equivalent efficiency requirements. If you receive an Air-Conditioning, Heating, and Refrigeration Institute (AHRI) Certificate, you will likely find the SEER2 or HSPF2 label on it. The same principle mentioned above applies today—the higher the value, the more efficient the system is. SEER2 still covers cooling efficiencies and HSPF2 still does the same for heating efficiencies.

When making recommendations, you’ll want to make sure the system meets any local or state requirements for minimum efficiency. Check with your local energy department. You’ll also want to look into rebates. Some utilities, jurisdictions, and the Inflation Reduction Act include funding for system replacements. If you’re pursuing a rebate, make sure the system you recommend meets those requirements.

One more thing: If you are working in a cold region, the Northeast Energy Efficiency Partnership (NEEP) hosts a cold-climate air-source heat pump (ccASHP) product list. If you are building or remodeling in a predominantly heating-dominated climate, you’ll want to make sure the equipment you have installed is verified to operate correctly in the low temperatures the home will experience.