Electrical units and conversion

BTU to watts — cooling capacity is not electrical power

Btu/h measures heat moved. Watts drawn from the wall depend on efficiency. This page converts both ways and keeps them apart, because dividing Btu/h by 3.412 gives cooling capacity in SI units, not power consumption.

How many watts does a given BTU rating use?

There are two different answers, and mixing them up is the usual mistake. As a unit conversion, 8,000 Btu/h ÷ 3.412141633 = 2,345 thermal watts — the same amount of heat, expressed in SI units. As electricity used, an air conditioner is a heat pump: it moves that heat using far less power than the heat itself represents. Input watts = Btu/h ÷ EER. So an 8,000 Btu/h unit rated at EER 11 draws about 727 W while cooling, and one rated at EER 14 draws about 571 W — same cooling, roughly 156 W apart. The BTU number alone cannot tell you the wattage; you need the unit's efficiency, and we do not guess one for you.

Your inputs

Cooling capacity

The rated cooling capacity on the nameplate or spec sheet. This is heat moved per hour, not electricity used.

Common room AC capacities

Which efficiency figure do you have?

Only EER can be converted to instantaneous watts. The others are defined below and are blocked here on purpose.

EER of your unit

From the spec sheet, the EnergyGuide label or the manufacturer's product data. There is no default here: no published source gives a defensible typical EER by capacity class, so guessing one would fabricate your answer.

Show running cost?

Cost is only offered because you supplied a real EER. It is computed from the derived watts by energyEngine-1.2.0.

Supply voltage (for the current check)

Enter the EER of your unit to get a watt figure

No efficiency is assumed here. 8,000 Btu/h is 2,345 thermal watts of heat moved per hour — an exact unit conversion that tells you nothing about electricity used. The electrical draw is Btu/h ÷ EER, so without an EER there is no defensible answer.

Look for "EER" on the EnergyGuide label, the specification sheet, the manufacturer's product page or the data plate on the unit. Some sheets list rated input watts directly, which answers the question outright. If only a CEER figure is given, see the section below on why it cannot be used here.

Same capacity, different efficiency, different watts

This is the whole point of the page. Every row cools identically — 8,000 Btu/h of heat removed per hour at the rating condition — and the electrical draw varies by nearly a factor of two. The last column is the coefficient of performance implied by the EER: units of heat moved per unit of electricity consumed. The EER values shown are illustrative spacing across the plausible range, not claims about what any particular product achieves.

Input watts = Btu/h ÷ EER, at the DOE rating condition (80 °F DB / 67 °F WB indoors, 95 °F DB outdoors). Computed by hvacEngine-1.0.0.
Cooling capacity	EER	Estimated active watts	Implied COP
8,000 Btu/h	8.0	1,000 W	2.34
8,000 Btu/h	9.5	842 W	2.78
8,000 Btu/h	11.0	727 W	3.22
8,000 Btu/h	12.5	640 W	3.66
8,000 Btu/h	14.0	571 W	4.10

Thermal watts versus electrical watts, by capacity

The second column is a pure unit conversion and is exact. The third and fourth columns are electrical input at two illustrative EER values, and are estimates that depend entirely on the unit. Reading the second column as "power consumption" is the error this page exists to prevent: it overstates the draw of a working air conditioner by roughly the COP.

1 W = 3.412141633 Btu/h (NIST SP 811, Appendix B.8). Electrical columns use EER 11 and EER 14 as illustrative values only — neither is a typical-efficiency claim.
Rated capacity	Capacity in thermal W	Input W at EER 11	Input W at EER 14
5,000 Btu/h	1,465 W	455 W	357 W
8,000 Btu/h	2,345 W	727 W	571 W
10,000 Btu/h	2,931 W	909 W	714 W
12,000 Btu/h	3,517 W	1,091 W	857 W
18,000 Btu/h	5,275 W	1,636 W	1,286 W

Why CEER is not a substitute for EER

CEER — combined energy efficiency ratio — is the metric the US federal standards for room air conditioners are written in, so it is often the only number on a spec sheet. It is not, however, an instantaneous ratio. CEER divides cooling capacity by a combined electrical energy figure that adds standby-mode and off-mode consumption over an assumed annual usage profile to the active cooling energy.

Because that denominator includes hours in which the unit produces no cooling at all, CEER is always lower than the same unit's EER. Dividing Btu/h by CEER therefore understates the draw of a running compressor — the calculator above blocks it rather than returning a plausible-looking wrong number. If CEER is all you have, treat it as an efficiency class indicator and look for the EER or the rated input watts in the product's technical data.

Do not mix these metrics

Four efficiency metrics circulate in air-conditioning specifications and only one of them inverts into a power figure. The calculator accepts EER and refuses the rest by design.

Metric contract enforced by hvacEngine-1.0.0. Anything marked 'No' throws rather than computing.
Metric	Valid as Btu/h ÷ metric = watts?	What it actually measures	Source
EER	Yes	Cooling capacity in Btu/h divided by electrical input power in watts, both measured at one steady-state rating condition: 80 °F dry-bulb / 67 °F wet-bulb indoors and 95 °F dry-bulb outdoors. Because both terms are instantaneous, the ratio inverts cleanly: input watts = Btu/h ÷ EER at that condition.	US DOE test procedure for room air conditioners, 10 CFR Part 430 Subpart B Appendix F (rating conditions per AHAM RAC-1 / ANSI-AHRI 210/240 as referenced there).
CEER	No	Cooling capacity divided by a combined electrical energy figure that adds standby-mode and off-mode power consumed over an assumed annual usage profile to the active cooling energy.	US DOE, 10 CFR 430 Subpart B Appendix F — definition of combined energy efficiency ratio, including standby and off-mode power.
SEER	No	Total seasonal cooling output in Btu divided by total seasonal electrical energy input in watt-hours, for central air conditioners and heat pumps, across a modelled distribution of outdoor temperatures and part-load operation.	US DOE, 10 CFR 430 Subpart B Appendix M (SEER) — central air conditioners and heat pumps.
SEER2	No	The same seasonal ratio as SEER, measured under the revised M1 test procedure with higher external static pressure. SEER2 values are numerically lower than SEER values for the same equipment.	US DOE, 10 CFR 430 Subpart B Appendix M1 (SEER2), effective for equipment manufactured from 1 January 2023.
SACC	No	A capacity metric, not an efficiency metric. For portable air conditioners, DOE derives SACC by testing at two outdoor conditions and applying a duct heat-transfer and infiltration-air correction, producing a capacity substantially below the marketed nameplate Btu/h.	US DOE, 10 CFR 430 Subpart B Appendix CC — test procedure for portable air conditioners (SACC and CEER for portable units).

Portable air conditioners: SACC is a different capacity

A portable air conditioner's marketed Btu/h and its DOE seasonally adjusted cooling capacity (SACC) are not the same number and are not interchangeable with a window unit's rated capacity. SACC is derived by testing at two outdoor conditions and correcting for duct heat transfer and for the infiltration air pulled into the room to replace what the exhaust hose expels, which is a real thermal penalty single-hose units carry and window units do not.

The practical consequence: a portable unit marketed at a given Btu/h will typically be rated substantially lower on SACC, so comparing a portable's nameplate figure with a window unit's rated capacity compares two different measurements. SACC is also a capacity, not an efficiency — it never belongs in the EER field.

Reference efficiency thresholds — not typical efficiencies

These are regulatory minima and a voluntary certification level, each with its source and effective date. They are not typical or average efficiencies, and this site will not present them as such: no authoritative source publishes a shipment-weighted typical efficiency by capacity class, and the DOE technical support documents model a regulatory distribution rather than measuring the units people actually own. That is why the calculator has no default EER and why we do not publish per-BTU cost pages.

Note the split year: 2026 has two different federal minimum tables depending on the date of manufacture, so a single undated "current minimum" would be wrong for half the year. Note also that all of these are expressed in CEER, which — as above — must not be typed into the EER field.

Thresholds only. Each row is a floor a unit must meet or a level it may certify to, never an estimate of what a given unit achieves.
Program	Applies to	Product class	Level	Source
DOE federal minimum	Units manufactured through 25 May 2026	Louvered, < 6,000 Btu/h (class 1)	CEER 11.0	10 CFR 430.32(b), Table 6
DOE federal minimum	Units manufactured through 25 May 2026	Louvered, 8,000–13,999 Btu/h (class 3)	CEER 10.9	10 CFR 430.32(b), Table 6
DOE federal minimum	Units manufactured through 25 May 2026	Louvered, ≥ 28,000 Btu/h (class 5b)	CEER 9.0	10 CFR 430.32(b), Table 6
DOE federal minimum	Units manufactured from 26 May 2026	Louvered, < 6,000 Btu/h (class 1)	CEER 13.1	10 CFR 430.32(b), Table 7 — final rule 88 FR 34298 (26 May 2023)
DOE federal minimum	Units manufactured from 26 May 2026	Louvered, 8,000–13,999 Btu/h (class 3)	CEER 16.0	10 CFR 430.32(b), Table 7 — final rule 88 FR 34298 (26 May 2023)
DOE federal minimum	Units manufactured from 26 May 2026	Louvered, ≥ 28,000 Btu/h (class 5b)	CEER 13.2	10 CFR 430.32(b), Table 7 — final rule 88 FR 34298 (26 May 2023)
ENERGY STAR (voluntary)	Room Air Conditioners v5.0, in force	Louvered room air conditioners, by class	CEER 13.7	ENERGY STAR Room Air Conditioners Program Requirements v5.0 — lowest qualifying level
ENERGY STAR (voluntary)	Room Air Conditioners v5.0, in force	Louvered room air conditioners, by class	CEER 14.7	ENERGY STAR Room Air Conditioners Program Requirements v5.0 — highest qualifying level

Provenance

Conversion constant: NIST Special Publication 811 (2008 edition), Appendix B.8 — 1 W = 3.412141633 Btu_IT/h.
EER and CEER definitions and rating conditions: US DOE test procedure for room air conditioners, 10 CFR Part 430 Subpart B Appendix F.
SEER and SEER2: 10 CFR Part 430 Subpart B Appendices M and M1 (M1 effective 1 January 2023).
Portable air conditioners, SACC: 10 CFR Part 430 Subpart B Appendix CC.
Federal minimum CEER levels: 10 CFR 430.32(b), Table 6 (manufactured through 25 May 2026) and Table 7 (manufactured from 26 May 2026, per final rule 88 FR 34298, 26 May 2023).
Voluntary certification levels: ENERGY STAR Room Air Conditioners Program Requirements v5.0.