Central A/C Tonnage to Generator Wattage Chart (2 to 5 Tons)
A 3-ton central A/C typically requires 15,000 surge watts without a soft-starter, but only 5,500 surge watts with one installed. Use our sizing chart to match compressor tonnage directly to required generator running and surge wattage.
01 The Direct Relationship Between HVAC Tonnage and Electrical Draw
One ton of cooling capacity equals 12,000 BTUs per hour. As tonnage increases, compressor displacement and electric motor horsepower grow proportionally.
While continuous running wattage remains moderate (typically 1,000 watts per ton), raw locked-rotor startup amperage spikes brutally on standard split systems.
NEC 220 mandates calculating 125 percent of continuous load plus the single largest motor startup surge. Unassisted central air conditioners draw 3 to 5 times running current during startup.
- Running power averages 900 to 1,200 watts per ton of cooling capacity.
- Starting surge without soft-start ranges from 45A on 2-ton to 135A on 5-ton.
- Adding soft-starters cuts peak wattage demand by more than half.
02 Comprehensive A/C Tonnage Sizing Matrix
Consult our engineering sizing table below to find exact generator wattage requirements for your home's central air conditioning system.
Calculate your specific compressor starting demands with our interactive Central A/C Soft-Start Sizer.
| A/C Tonnage | Running Amps (RLA) | Standard LRA Surge | Surge with Soft-Start | Min Generator Size |
|---|---|---|---|---|
| 2.0 Ton (24,000 BTU) | 10A to 12A (2,600W) | 55A (13,200W) | 18A (4,300W) | 6,500W Inverter |
| 3.0 Ton (36,000 BTU) | 14A to 17A (3,800W) | 80A (19,200W) | 26A (6,200W) | 8,500W Inverter |
| 4.0 Ton (48,000 BTU) | 18A to 22A (4,800W) | 110A (26,400W) | 35A (8,400W) | 10,500W Inverter |
| 5.0 Ton (60,000 BTU) | 24A to 28A (6,200W) | 135A (32,400W) | 42A (10,000W) | 12,000W Inverter |
NEC 220 mandates calculating 125 percent of continuous load plus the single largest motor startup surge. Unassisted central air conditioners draw 3 to 5 times running current during startup.
03 Accounting for Air Handler Blowers and Head Pressure
Do not forget that your home's indoor furnace blower motor runs simultaneously with the outdoor condenser, adding 400 to 800 continuous watts.
Ensure your generator fuel choice provides adequate headroom, accounting for the natural gas derate using our Derating Waterfall Sizer.
NEC 220 mandates calculating 125 percent of continuous load plus the single largest motor startup surge. Unassisted central air conditioners draw 3 to 5 times running current during startup.
- 1 Check Condenser Nameplate: Record RLA (running amps) and LRA (locked-rotor amps) from the label.
- 2 Add Furnace Blower: Add 600 watts to running calculations for the indoor circulation fan.
- 3 Apply Fuel Derating: Deduct twenty percent from generator capacity if fueling with natural gas.
- A/C running draw averages 1,000W per ton; starting surge reaches 5x running draw.
- Soft-starters reduce starting spike from 110A down to 35A on 4-ton compressors.
- Account for indoor air handler blowers and fuel derating factors.
Frequently Asked Questions
Q: Can an 8,000-watt generator run a 3-ton air conditioner?
Yes, if an electronic soft-starter is installed. Without a soft-starter, the 80-amp startup surge will trip the generator breaker instantly.
Q: What is the difference between RLA and LRA on an A/C nameplate?
RLA stands for Rated Load Amps (normal running current). LRA stands for Locked-Rotor Amps (the momentary electric motor spike when starting).
Q: Why does my generator stall when the A/C tries to restart quickly?
Compressor refrigerant head pressure requires several minutes to equalize. Restarting against high head pressure spikes amperage above normal starting limits.