How many watts does an air conditioner use? Real numbers by BTU.
A 12,000 BTU window unit pulls about 1,050 W running. A 36,000 BTU central system pulls 3,500–4,500 W. Here's the wattage and the cost per hour for every common AC type in 2026.
Wattage formula
An AC's nameplate gives you either watts directly or BTU/hr cooling capacity and an efficiency rating. The conversion:
watts = BTU/hr ÷ EER cost_per_hour = (watts ÷ 1000) × rate
EER (Energy Efficiency Ratio) is BTU per watt at fixed test conditions. SEER and SEER2 are seasonal versions used for central systems — divide SEER by 1.1 for a rough EER equivalent.
Wattage by AC type
| Type | Typical BTU | Watts (running) | $/hour @ $0.175 |
|---|---|---|---|
| Small window unit | 5,000–6,000 | 450–550 | $0.08–$0.10 |
| Medium window | 8,000–10,000 | 700–900 | $0.12–$0.16 |
| Large window | 12,000–15,000 | 1,000–1,300 | $0.18–$0.23 |
| Portable AC | 8,000–14,000 | 900–1,500 | $0.16–$0.26 |
| Mini-split 1-zone | 9,000–18,000 | 500–1,400 | $0.09–$0.25 |
| Central 2 ton | 24,000 | 2,000–3,000 | $0.35–$0.53 |
| Central 3 ton | 36,000 | 3,000–4,500 | $0.53–$0.79 |
| Central 5 ton | 60,000 | 5,000–7,000 | $0.88–$1.23 |
Window vs central — one cooling season, same hours
Inputs: a 12,000 BTU window unit (1,050 W) vs a 3-ton central system (3,500 W, the low end of its 3,000–4,500 W range), both at the US average rate of $0.175/kWh. We assume a 4-month cooling season (120 days) and 8 compressor-hours per day — that is the AC running 16 h/day at the 50% duty cycle described below, so only half of those hours draw power.
| Window — 1.05 kW × 8 h × 120 days = 1,008 kWh | $176 / season |
| Central 3 ton — 3.5 kW × 8 h × 120 days = 3,360 kWh | $588 / season |
| Difference — 2,352 kWh | $412 / season |
Different wattage, rate, or season length? Drop your own numbers into the electricity cost calculator for your exact figure.
Monthly cost: what you'll really pay
Hourly cost only tells half the story — your AC doesn't run 24/7. Compressor duty cycle averages 30–70% during use. Typical summer-month bill addition by climate:
- Mild summer (Pacific NW): central 3 ton, ~$50–$80/month June–August.
- Moderate (Northeast, Midwest): ~$80–$140/month June–August.
- Hot (Texas, Florida, Phoenix): ~$200–$380/month May–September. Phoenix peak bills can hit $450.
Should you upgrade to a higher-SEER unit?
Wattage scales inversely with efficiency: the same cooling output through a SEER2 22 system draws far fewer watts than through an old SEER2 14 one. For the 3-ton central system above (3,500 W, ~SEER2 14), moving to a SEER2 22 inverter unit cuts running power to about 2,230 W — roughly $214 less per cooling season on the same 8 compressor-hours/day. That number is the lever; here's when it's worth pulling.
Upgrade to a higher-SEER unit if…
- Your current system is SEER2 14 or lower (anything 12+ years old usually is).
- You run AC hard for 4+ months a year, so the ~$214/season saving compounds.
- Your rate is above $0.175/kWh, or a tiered/peak plan pushes summer load into a high bracket.
- The old unit is near end of life anyway — replace it with an inverter mini-split or SEER2 18–22 central, not like-for-like.
Keep yours if…
- Your unit is already SEER2 16+ — the extra efficiency gain is small and the payback stretches past the unit's remaining life.
- You only cool a few weeks a year (mild climate, short season).
- You cool one or two rooms — a $200–$400 window or portable unit beats a multi-thousand-dollar central swap.
- The cheap wins still on the table — filter, setpoint, smart thermostat, shaded condenser — would close most of the gap first.
5 ways to cut AC wattage
- Raise the setpoint 2 °F. Saves ~6–10% on cooling.
- Clean the filter monthly. Dirty filter cuts efficiency by up to 15%.
- Use a smart thermostat with schedule. 5–8% savings, no comfort loss.
- Shade the outdoor condenser. 5–10% reduction in compressor load on sunny days.
- Switch to a heat pump / mini-split with inverter compressor. 30–50% less electricity than fixed-speed AC.
Run your AC through the calculator
The general electricity cost calculator takes wattage and hours and gives you daily/monthly/yearly. For whole-home electrification with a heat pump that also heats, see the heat pump calculator.
Frequently asked questions
What is EER vs SEER vs SEER2?
EER is efficiency at a fixed 95 °F test. SEER averages across a cooling season. SEER2 (mandatory since 2023) uses a more rigorous test reflecting real ductwork pressure — SEER2 ≈ SEER × 0.95.
Does running the AC longer at a higher temp save electricity?
Generally no — the more efficient strategy is to set it once at your comfort temp and let it cycle. Setbacks save energy only when the house is unoccupied for 8+ hours.
Are portable ACs really less efficient?
Yes. Portable units have a single exhaust hose that depressurizes the room, drawing in hot outside air through every gap. Real efficiency is 20–40% worse than the nameplate suggests. Window units always win on $/BTU.