A typical 3-ton central air conditioner uses about 3,500 watts while running (outdoor unit plus blower), and roughly 2,000-6,000 W across 2- to 5-ton systems. Expect a starting surge around 7,000 watts on 240 volts.
- Running watts
- 3,500 WTypical; 2,000–6,000 W across models
- Starting watts
- 7,000 WOur ~7,000 W is an estimate for a 3-ton unit; Generac's sizing guide…
- Per day
- 29.4 kWh24 h of use, cycling
- Current
- 14.6 AAt 240 V while running
Figures checked against DOE, ENERGY STAR and manufacturer data on . Your model's label is the final word.
Watts by model and setting
Most central air conditioner models draw between 2,000 and 6,000 W while running; a typical one draws about 3,500 W. Assumes a 3-ton system (outdoor unit plus indoor blower) at about 3,500 W running 35% of a hot summer day; mild days use much less.
- Capacity in tons (1 ton = 12,000 BTU/h): power rises roughly in step with size
- Efficiency rating: newer systems are rated in SEER2/EER2; since 2023 the minimum is 13.4 SEER2 in the North and 14.3 SEER2 in the South
- Single-stage vs two-stage or variable-speed (inverter) compressors
- Outdoor temperature, duct leaks, dirty filters/coils and the thermostat setting
- Indoor blower motor type: an older PSC furnace blower adds more watts than an ECM blower
Running a central air conditioner on backup power
This is a 240 V appliance. It needs a generator with a 240 V outlet or a transfer switch or interlock installed by a licensed electrician; most portable power stations only supply 120 V.
- Central AC runs on a 240 V circuit, so it needs a 240 V generator connected through a transfer switch or interlock installed by an electrician; never backfeed through a dryer outlet
- Most portable generators cannot start a 3-ton AC; whole-home standby generators of about 15-22 kW typically can, especially with a soft-start kit
- The indoor furnace or air-handler blower must also be powered for the system to work
- Portable power stations generally cannot run central AC unless they are a 240 V whole-home battery system sized for the surge
Add it to the generator calculator
Questions people ask
What size generator do I need to run central air?
For a 3-ton system, plan on a generator that can supply around 7,000 W of starting power plus your other loads; many homes use a standby generator in the 15-22 kW range or add a soft-start kit.
How many watts per ton does central AC use?
Roughly 1,000-1,200 W per ton for a modern system, more for older or lower-SEER units.
Will a soft start let a smaller generator run my AC?
Often yes. A soft-start kit lowers the compressor's inrush current, which can let a smaller generator start the unit, but confirm with an HVAC pro.