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EER, COP and kW/ton Converter

Convert an efficiency rating between EER, COP and kilowatts per ton, or a heat pump’s HSPF2 to a seasonal COP, using exact factors.

Method reviewed October 25, 2026. Version 1.0.0. How it works

Your inputs

Result

EER
12
COP
3.52
kW per ton
1

EER 12 = COP 3.52 = 1 kW/ton.

  • SEER2 is a seasonal figure and cannot be converted to EER2 by a fixed factor; the relationship depends on the equipment.
Show the working
  1. COP = EER ÷ 3.412
    12 ÷ 3.41214 = 3.517
  2. kW/ton = 12 ÷ EER (12,000 BTU/h per ton ÷ 1,000 W/kW)
    12 ÷ 12 = 1

The conversions

  • EER is BTU/h of cooling per watt of electricity.
  • COP is the same ratio in consistent units, so EER = COP × 3.412.
  • kW/ton is electrical input per ton of cooling: kW/ton = 12 ÷ EER, because one ton is 12,000 BTU/h.
  • HSPF2 is seasonal BTU of heat per watt-hour, so the seasonal COP = HSPF2 ÷ 3.412.

The factor 3.412 is 3.41214 BTU/h per watt (NIST).

What cannot be converted

SEER2 and EER2 measure different things: SEER2 is a seasonal average over a range of outdoor temperatures, EER2 is measured at one hot condition. There is no fixed factor between them; it depends on how the equipment performs at part load. Use the manufacturer’s rated EER2 if you need it.

Worked example

These are the example values the calculator opens with, and the result the engine calculates for them.

Inputs

I have
EER (or EER2), BTU/Wh
Value
12

Result

EER
12
COP
3.52
kW per ton
1

EER 12 = COP 3.52 = 1 kW/ton.

Assumptions

  • 1 watt = 3.41214 BTU/h; 1 ton of refrigeration = 12,000 BTU/h (NIST).

Limitations

  • Converts ratings; it does not change the test conditions they were measured at.

Frequently asked questions

What is a good COP?

For air-source heat pumps, rated heating COPs are commonly around 3–4 at 47 °F and lower in cold weather. Chillers are usually rated in kW/ton, where lower is better.

Is kW/ton the same as EER?

They describe the same thing in opposite directions: kW/ton is input per output, EER is output per input. A 1.0 kW/ton unit has an EER of 12.

Can I convert SEER to EER?

Not with a fixed factor. Rules of thumb exist, but the relationship varies between equipment, especially variable-speed units, so use the rated EER2 from the AHRI certificate or product literature.

Sources

  1. NIST Guide to the SI (SP 811), Appendix B.9 — conversion factors — National Institute of Standards and Technology. 1 ton of refrigeration = 12,000 BTU/h; 1 BTU/h = 0.2930711 W; 1 atm = 101.325 kPa.
  2. Calculating 5 °F heat pump performance — U.S. DOE. COP = heating output ÷ (3.412 × input watts).
  3. 2023 Central Air Conditioner Standards — FAQ — U.S. DOE, Office of Energy Efficiency & Renewable Energy. Regional SEER2 / EER2 / HSPF2 minimum efficiencies effective 2023.

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