How much electricity does an AC use, and how do you estimate yours?
There is no single number, because it depends on the unit, the house and the weather. There is a simple way to work out your own.
The short answer
It depends on the type of AC, its efficiency, its size and how many hours it runs. A central system uses far more power than a window unit, but it also cools far more space.
Quoting one figure for all air conditioners would be misleading. Use the method below to get a number for yours.
How do you estimate your own AC's use?
Electricity is billed in kilowatt-hours (kWh). One kWh is one kilowatt running for one hour.
The math is short: watts times hours of running, divided by 1,000, gives kWh. Find the watts on the nameplate or in the manual. If you only see amps and volts, multiply them to get watts.
Then count how many hours the compressor actually runs, not how many hours the thermostat is set to cool. A unit cycles on and off, so real running time is less than clock time.
Multiply kWh by the rate on your utility bill and you have a cost. Your own rate is the only reliable one, since rates vary by state and utility.
What changes how much power it draws
| Factor | Effect |
|---|---|
| Efficiency rating (SEER2) | Higher rating means less electricity for the same cooling |
| Size of the unit | Bigger units draw more when they run |
| Outdoor temperature | Hotter days mean longer run times |
| Insulation and shade | A leaky, sunny house makes the AC work longer |
| Thermostat setting | A bigger gap between inside and outside means more running |
| Dirty filter or coil | Restricted airflow makes the system work harder |
Central AC versus window and portable units
A central system has a more powerful compressor and a blower that moves air through ducts. A window unit is smaller and cools one room.
Compare them per square foot cooled, not by the total. A small unit trying to cool too large a space will run constantly and use plenty of power while still falling short.
Ways to use less
Change the filter on schedule and keep the outdoor unit clear of leaves and debris. Close blinds on sunny windows. Raise the thermostat a few degrees when you are out, rather than turning the system off, so it does not have to fight a hot house.
Be honest about the limits: a very old or oversized unit may cost more to run than the fixes can recover. A licensed technician can tell you whether repair or replacement makes sense. Leave refrigerant and electrical work to them.
This article does not quote prices, rebates or tax credits, because they change by state and utility.
Frequently asked questions
How do I calculate how much electricity my AC uses?
Multiply the unit's watts by the hours the compressor runs, then divide by 1,000 to get kWh. Multiply by your utility rate for the cost.
Does a higher SEER2 rating save electricity?
Yes. A higher SEER2 means the unit delivers the same cooling with less electricity. How much you save depends on how often you run it.
Does turning the AC off when I leave save energy?
Often a modest setback works better than shutting it off. A hot house takes a long time to cool, and the system may run hard to catch up.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- ENERGY STAR. Energy Savings at Home: Heating & Cooling
- US EPA. Section 608 of the Clean Air Act