SEER EER HSPF Converter

HVAC Efficiency Metrics Explained

SEER, EER, HSPF, and COP all measure how efficiently a heat pump or air conditioner converts electric energy into cooling or heating. The big differences are: what conditions the test is run under, whether it covers a single moment or a whole season, and whether the result is dimensionless or in BTU per watt-hour.

The Three Categories

Steady-state metrics (EER, EER2, COP) measure efficiency at one fixed operating point. EER and EER2 use 95 °F outdoor / 80 °F indoor and are given in BTU/Wh. COP is dimensionless — just heat out divided by electricity in. Seasonal metrics (SEER, SEER2, HSPF, HSPF2) simulate an entire cooling or heating season with varying outdoor temperatures and report an average. They are given in BTU/Wh too. Seasonal values are higher than steady-state because the average operating conditions are milder than the design point.

SEER vs SEER2

In January 2023 the US DOE switched to SEER2, EER2, and HSPF2 test procedures. The new tests use higher blower external static pressure (0.5 iwc instead of 0.1-0.2 iwc) to better reflect real-world duct systems. This drops ratings about 4-5% for SEER, 4-5% for EER, and 14-15% for HSPF. A 16 SEER unit becomes approximately 15.2 SEER2. A 10 HSPF becomes 8.5 HSPF2. The equipment is the same; the test method is stricter.

Converting Between Them

Rough relationships at typical rating conditions: SEER ≈ EER × 1.12 (the SEER-to-EER ratio averaged across modern equipment), SEER ÷ 3.412 ≈ seasonal cooling COP, HSPF ÷ 3.412 ≈ seasonal heating COP. These are approximations — exact conversion depends on the specific unit's capacity curve. For quick comparison shopping and budget analysis, they're more than accurate enough.

DOE Minimum Efficiency Standards (2023 SEER2/HSPF2)

Current US DOE minimum efficiency for new residential split-system installations as of Jan 1, 2023:

ENERGY STAR thresholds (2024): central AC ≥ 15.2 SEER2 + 12.0 EER2 (South), heat pumps ≥ 15.2 SEER2 + 8.1 HSPF2. Mini-splits ≥ 16.0 SEER2 + 9.0 HSPF2. NEEP cold-climate heat pump qualification requires COP ≥ 1.75 at 5 °F and capacity ≥ 70% of rated at 5 °F.

Typical Residential Ratings by Tier

• Code-minimum: SEER2 14.3 / HSPF2 7.5 (standard single-stage)
• Mid-range: SEER2 16-18 / HSPF2 8.5-9.0 (2-stage)
• High efficiency: SEER2 18-21 / HSPF2 9.5-10.5 (variable-speed)
• Premium cold-climate: SEER2 22-27 / HSPF2 10-13 (NEEP-listed inverter)

Frequently Asked Questions

Which rating should I use to compare units?

Compare same-era ratings: SEER2 to SEER2, SEER to SEER. Don't compare a pre-2023 SEER 16 unit to a post-2023 SEER2 15 unit directly.

What's a good SEER2 today?

14.3 SEER2 is the southern minimum. 16 SEER2 is mid-range, 18-20 SEER2 is high efficiency, 22+ SEER2 is premium inverter.

Does higher SEER always save money?

Not always — the upgrade cost has to be recouped from energy savings. Use this calculator along with operating cost estimates to compare payback.

What is a good COP for a heat pump?

At 47 °F rating: standard = 3.5-4.0, premium inverter = 4.5-5.0. At 17 °F: standard drops to 2.5, cold-climate inverter stays around 3.0.

Why do commercial systems use kW/ton?

kW/ton = 12 ÷ EER. A 12 EER = 1.0 kW/ton. Commercial engineers prefer kW/ton because it scales with tonnage and relates directly to electrical demand.