What 3,412 BTU per Kilowatt-Hour Says About EER, SEER2 and COP
Stand in front of two air conditioners and the yellow labels are speaking different languages. One quotes capacity in BTU per hour and efficiency as SEER2; a heat pump beside it adds HSPF2; the imported inverter unit at the end of the aisle gives kilowatts of output and a COP. All four ratings are built on the same bridge — the number of BTU carried by one kilowatt-hour of electricity — and once that constant is in front of you the labels collapse into a single comparable scale.
What Each Rating on the Label Measures
EER Is a Mixed-Unit Ratio
COP Is the Same Number Without Units
Seasonal Ratings Average a Whole Year
Moving Heat Beats Making It
Comparing Two Quotes on the Same Efficiency Scale
The point of the conversion, on a shopping trip, is to stop comparing a rating against a rating and start comparing heat delivered against electricity bought.
Start from one kilowatt-hour
Leave 1 in the left field and note that a kilowatt-hour is 3,412.13 BTU of raw electrical energy. That is the baseline every rating is measured against, and the only figure a resistance heater can ever deliver.
Multiply by the rating to get heat moved
Multiply the baseline by the unit's COP, or simply multiply the SEER2 or EER2 figure by 1,000 — the arithmetic works out identically, because a rating point is one BTU per hour per watt.
Turn a catalogue BTU figure back into kWh
When a quote states seasonal output in BTU and you want the electricity behind it, the swap arrows reverse the pair; either field accepts typing, so the comparison runs in whichever direction the paperwork was written.
Carry the figures into your own comparison
The copy control above each field gives the plain digits with no unit attached, so two or three candidate units can be lined up in a spreadsheet and priced against your actual tariff.
Efficiency Ratings and the Heat Each Moves per Kilowatt-Hour
Every rating in the first column is BTU/h of output per watt of input, so multiplying by 1,000 gives the BTU moved for each kilowatt-hour consumed. The COP column is the same rating divided by 3.4121, and the first row is the fixed ceiling for anything that makes heat rather than moving it.
| Rating | What it describes | Equivalent COP | Heat moved per kWh (BTU) |
|---|---|---|---|
| Electric resistance | Baseboard, strip heat, immersion element | 1.00 | 3,412 |
| EER2 8.0 | Aging window unit at design conditions | 2.34 | 8,000 |
| EER2 10.0 | Current room air conditioner, peak condition | 2.93 | 10,000 |
| HSPF2 7.5 | US minimum heat-pump heating season | 2.20 | 7,500 |
| HSPF2 8.8 | Better-than-minimum heating season | 2.58 | 8,800 |
| SEER2 13.4 | US northern minimum for split cooling | 3.93 | 13,400 |
| SEER2 14.3 | US southern minimum for split cooling | 4.19 | 14,300 |
| SEER2 20.0 | High-end inverter mini-split | 5.86 | 20,000 |
The first row is the whole argument for heat pumps in four digits. Electricity that is burned in a resistance element yields 3,412 BTU and stops there; the same kilowatt-hour through a heat pump running at a seasonal COP of 2.58 carries 8,800 BTU into the house, and a good inverter unit in cooling mode shifts nearly six times its own energy. Cooling and heating figures are not interchangeable, though — a machine with a headline SEER2 of 20 might carry an HSPF2 in the eights, because winter conditions are simply harder.
What This Page Does While You Shop
Two Quotes Compared Without Retyping
Put one unit's annual electricity in the left box, note the BTU, then overwrite with the rival's number. Neither side is fixed, so alternatives are a keystroke apart rather than a fresh sum.
Bare Rating Digits for a Side-by-Side Sheet
Copying with the button or Ctrl+C in the field hands over the number alone, ready to multiply by your own per-kWh rate in a shortlist spreadsheet.
Metric Catalogue Units a Click Away
The searchable lists on both sides hold all 23 energy units, so a European brochure quoting kilojoules or megajoules of seasonal output lands on the same scale as a US label without a second tool.
Season-Long Output Without Crowded Digits
A year of cooling runs to millions of BTU. Thousands are spaced apart instead of packed together, so an annual figure can be read and checked rather than counted digit by digit.
Rating-Label Questions Before You Sign the Quote
What is the arithmetic between an EER number and a COP number?
Divide EER by 3.4121 for COP, multiply COP by 3.4121 to go back. EER is BTU/h of output per watt of input, and since one watt is 3.4121 BTU/h, dividing by that constant puts both sides of the ratio in watts and cancels the units away. So EER 11.94 is COP 3.50, EER 13.65 is COP 4.00, and a unit somebody describes as “COP 3” is sitting at EER 10.24. The constant is the same 3,412 BTU per kilowatt-hour scaled down by a thousand, which is why this one number underpins every efficiency label in the aisle.
What actually changed when SEER became SEER2?
The test conditions, not the machinery. From 2023 the US test procedure raised the external static pressure the equipment must work against from 0.1 to 0.5 inches of water column, which is far closer to the ductwork a system meets in a real house. Running the fan harder lowers the measured score, so the same equipment scores roughly 4.5–5 % lower as SEER2 than it did as SEER, and about 15 % lower as HSPF2 than as HSPF. A SEER 15 unit re-tested lands near SEER2 14.3. Comparing a new quote's SEER2 with an old brochure's SEER therefore flatters the older equipment by several percent.
How can one kilowatt-hour move more than 3,412 BTU of heat?
Because the electricity is not the source of the heat, only the means of transport. A heat pump uses its kilowatt-hour to run a compressor that raises refrigerant to a temperature above the indoor air, having already picked up thermal energy from outdoor air that cost nothing. The 3,412 BTU of electrical energy also ends up indoors, on top of everything the cycle carried in, so nothing is created out of nothing. That is why the ratio is called a coefficient of performance rather than an efficiency: efficiency above 100 % would be nonsense, but moving three or four units of heat with one unit of work is ordinary thermodynamics.
Is HSPF2 just a seasonal COP in disguise?
Essentially, yes. HSPF2 is total heating BTU delivered across the season divided by total watt-hours drawn, so it has the same BTU-per-watt-hour shape as EER and converts the same way: the US minimum of 7.5 is a seasonal COP of 2.20, and 8.8 is 2.58. Two things are folded into it that a nameplate COP hides — the defrost cycles the outdoor coil needs, and any supplementary resistance heat the controller calls on during cold snaps. That backup element runs at COP 1.00, so a system that leans on it heavily can post a disappointing HSPF2 even with a strong compressor.
A European unit is rated in kW and a US one in BTU/h — which is more efficient?
Put both on the COP scale first, because capacity and efficiency are separate questions. A 3.5 kW cooling output is 11,942 BTU/h, so that machine is the near-equivalent of a nominal 12,000 BTU/h US unit — the same size, differently labelled. Efficiency then comes from the European SEER or SCOP figure against the US SEER2, and the two are not directly comparable even after the unit conversion, because the seasonal test conditions and climate profiles behind them differ. Converting a brochure's kW output to BTU/h settles capacity; only a rating measured under the same procedure settles efficiency.
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