How Many Watts Does a Central Air Conditioner Use? Tons, EER2 and kWh
By Seamless Home Team, Home services operations · November 10, 2026 · Updated November 10, 2026
Quick answer
A central air conditioner's running watts at the federal test condition are its cooling capacity in Btu per hour divided by its EER2 rating — the Department of Energy defines EER as Btu per hour of cooling per watt of power input at 95°F. One ton is 12,000 Btu per hour, so a 3-ton (36,000 Btu/h) system rated 11.7 EER2 draws about 36,000 ÷ 11.7 ≈ 3,080 watts at that condition. Seasonal energy follows SEER2 instead: kWh ≈ Btu of cooling delivered ÷ SEER2 ÷ 1,000. The condenser's nameplate (volts, RLA, MCA, MOCP, LRA) is what sizes the circuit and any backup.
Central air conditioning is usually the single biggest electrical load in a house during summer, and it is also the one people most often guess at. There is no single "central AC wattage." The draw depends on how big the system is, how efficient it is, and how hot it is outside. The good news is that the federal efficiency ratings were designed to turn those three things into watts and kilowatt-hours with simple division.
This page is the whole-house companion to how many watts a window AC uses. The arithmetic is the same; the system is bigger and runs at 240 volts.
The formula: Btu per hour ÷ EER2
The Department of Energy defines the energy efficiency ratio (EER) as cooling capacity in Btu per hour divided by power input in watts, measured at 95°F outdoors — the condition where an air conditioner is working its hardest. Since January 1, 2023, ratings use EER2, measured under DOE's revised test procedure. Rearranged:
Running watts (at 95°F) ≈ cooling capacity (Btu/h) ÷ EER2
Central systems are sold in tons. One ton of cooling is 12,000 Btu per hour. So:
| System size | Capacity | At 11.7 EER2 | At 11.2 EER2 |
|---|---|---|---|
| 2 ton | 24,000 Btu/h | ≈ 2,050 W | ≈ 2,140 W |
| 3 ton | 36,000 Btu/h | ≈ 3,080 W | ≈ 3,210 W |
| 4 ton | 48,000 Btu/h | ≈ 4,100 W | ≈ 4,290 W |
| 5 ton | 60,000 Btu/h | ≈ 5,130 W | ≈ 5,360 W |
The two EER2 columns are DOE's Southwest minimums for split systems (11.7 below 45,000 Btu/h, 11.2 at or above), used here only because they are published numbers. They are not a claim about your unit. Look up your system's actual EER2 on its AHRI certificate or the manufacturer's spec sheet, using the model numbers on both the outdoor condenser and the indoor coil — the rating is for the matched pair.
Two caveats. EER2 describes one hot condition. On an 85°F day the same system draws less; on a 105°F day, more. And a higher-SEER2 variable-speed system often runs for long stretches at part load, far below its full-capacity watts.
SEER2 is for the season, not the moment
The seasonal energy efficiency ratio (SEER) is total cooling delivered over a cooling season divided by total electricity used over the same season. SEER2 is the version measured under the 2023 test procedure. It answers the bill question, not the circuit question:
kWh ≈ Btu of cooling delivered ÷ SEER2 ÷ 1,000
Worked example, with the hours stated as an assumption: a 3-ton system that runs the equivalent of 200 full-load hours in a month delivers 36,000 × 200 = 7.2 million Btu. At 14.3 SEER2 that is 7,200,000 ÷ 14.3 ÷ 1,000 ≈ 500 kWh for the month. At 13.4 SEER2, about 540 kWh. Change the hours and the answer moves in proportion. The watts to kWh calculator does the same arithmetic from a running wattage and runtime.
What the federal minimums are
DOE's standards for split-system central air conditioners installed on or after January 1, 2023:
| Region | Under 45,000 Btu/h | 45,000 Btu/h and up | Southwest EER2 |
|---|---|---|---|
| North | 13.4 SEER2 | 13.4 SEER2 | — |
| Southeast | 14.3 SEER2 | 13.8 SEER2 | — |
| Southwest (AZ, CA, NV, NM) | 14.3 SEER2 | 13.8 SEER2 | 11.7 / 11.2 (9.8 if SEER2 ≥ 15.2) |
Single-package air conditioners have a 13.4 SEER2 national minimum and a 10.6 EER2 minimum in the Southwest. DOE notes that SEER2 and EER2 numbers are similar to the older SEER and EER, but not directly comparable — an older "14 SEER" label is not the same as 14 SEER2.
Reading the condenser nameplate
The outdoor unit's data plate is the document that sizes the circuit:
- Voltage — usually 208/230 V single-phase for a home.
- RLA (rated load amps) for the compressor and FLA (full-load amps) for the condenser fan motor.
- MCA (minimum circuit ampacity) — the smallest wire ampacity the circuit may use.
- MOCP (maximum overcurrent protection) — the largest breaker allowed.
- LRA (locked-rotor amps) — the momentary current when the compressor starts.
Volts × (RLA + FLA) gives a rough upper bound on the outdoor unit's running watts; actual draw is usually lower, and power factor means amps × volts is not exactly watts for a motor. The indoor air handler or furnace blower is a separate load with its own nameplate — add it if you are adding up a whole system. The watts to amps calculator converts between the two at 240 volts.
What changes the number in your house
- Outdoor temperature. Higher condenser temperatures raise watts and lower capacity at the same time.
- Thermostat setting and runtime. Lower setpoints add hours; hours drive kWh.
- Duct leakage and insulation. Lost cooling has to be made up with more runtime.
- Single-stage versus variable-speed. A variable-speed system spends more time at low watts.
- Dirty filters and coils. Restricted airflow makes the system work harder for the same comfort.
None of those substitutes for a measurement if you need one house's number. A whole-home energy monitor with the AC circuit labeled, or your utility's hourly usage data, shows real watts and kWh.
Central air and a home battery
For backup power, two numbers matter: the running watts the inverter must supply continuously and the starting surge when the compressor kicks on, which the LRA on the nameplate indicates. A battery system that can carry 3,000 W steadily may still trip on a compressor start if its surge rating is too low. Soft starters reduce that inrush and are a common add-on when central air has to stay on.
Energy is the other limit. At roughly 3 kW running, a 3-ton system cycling half the time uses about 1.5 kWh per hour — a large share of a typical home battery over a long outage. That is why many critical load panel designs keep refrigeration, medical devices, lights and the furnace blower, and leave central air for when the grid returns. A heat pump faces the same trade-off in both seasons, and how many watts a house uses shows where air conditioning sits in the whole-home picture.
What this means for a Seamless visit
When we look at an air conditioning circuit or a home battery backup design, we start from the condenser nameplate and the system's certified EER2 and SEER2, not from a website average. The DOE definitions above let you turn those ratings into watts and kWh yourself. If you are replacing a system, our HVAC page covers how we scope the job.
Sources
- U.S. Department of Energy, 2023 Energy Conservation Standards for Residential Central Air Conditioners and Heat Pumps — FAQ — definitions of EER and SEER; SEER2/EER2 metrics; national and regional minimums effective January 1, 2023; Southwest region states.
- The data plate on your outdoor condenser (volts, RLA, FLA, MCA, MOCP, LRA) and the AHRI certificate for your matched condenser and coil.
Frequently asked questions
How many watts does a central air conditioner use?
Divide the cooling capacity in Btu per hour by the EER2 on the AHRI certificate or spec sheet. A 2-ton (24,000 Btu/h) system at 11.7 EER2 is about 2,050 watts at the 95°F test condition; a 3-ton at the same rating is about 3,080 watts; a 4-ton (48,000 Btu/h) at 11.2 EER2 is about 4,290 watts. Those are arithmetic examples from DOE's definition, not measurements of your house. Real draw rises on hotter days and falls on milder ones.
What is the difference between EER2 and SEER2?
EER2 is efficiency at a single hot condition (95°F outdoor), so it predicts running watts when the system is working hardest. SEER2 is the ratio of total cooling delivered over a season to total electricity used, so it predicts seasonal kWh. DOE's 2023 standards are expressed in both, measured under the revised test procedure.
What are the minimum efficiency standards for a new central AC?
For split-system air conditioners installed from January 1, 2023, DOE requires at least 13.4 SEER2 in the North and 14.3 SEER2 in the Southeast and Southwest for units under 45,000 Btu/h (13.8 SEER2 at 45,000 Btu/h and above). The Southwest also has EER2 minimums: 11.7 below 45,000 Btu/h and 11.2 at or above, dropping to 9.8 for units certified at 15.2 SEER2 or higher.
How do I find my AC's watts from the nameplate?
The outdoor condenser's data plate lists voltage (typically 208/230 V), the compressor's rated load amps (RLA), the fan motor's full-load amps (FLA), minimum circuit ampacity (MCA) and maximum overcurrent protection (MOCP). Volts × (RLA + FLA) is a rough upper bound on running watts for the outdoor unit. The indoor air handler or furnace blower adds its own draw on a separate nameplate.
How many kWh does central air use per month?
kWh ≈ Btu of cooling delivered ÷ SEER2 ÷ 1,000. A 3-ton system running the equivalent of 200 full-load hours in a month delivers 7.2 million Btu; at 14.3 SEER2 that is about 500 kWh. The hours are an assumption for the arithmetic. Your utility's interval data, or a whole-home monitor, gives the real number.
Can a home battery run central air in an outage?
Sometimes. The inverter has to supply both the running watts and the compressor's starting surge — shown as locked-rotor amps (LRA) on the condenser plate — and the battery has to hold enough kWh for the hours you want. Many backup designs leave central air off the critical load panel or add a soft starter to cut the inrush. We check the nameplate and the inverter's surge rating before saying yes.