HVAC Generator Load Calculator
Size your generator correctly for Central Air Conditioners, Heat Pumps, and Electric Furnaces. Account for starting wattage surges and auxiliary electric heat strips.
System Specifications
*Caution: Heat strips consume massive power (1kW = 1000W).
Reduces AC startup surge by up to 70%
Required Generator Output
Running Load
-- W
Amps (240V)
-- A
Recommended HVAC Generator Gear
Essential equipment for running air conditioners on backup power.
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Soft Start Kits
Reduce AC startup surge by up to 70%.
View on Amazon →Inverter Generators
Quiet, clean power perfect for AC units.
View on Amazon →Hard Start Kits
Cost-effective help for starting older compressors.
View on Amazon →Transfer Switches
Safely connect generator to home panel.
View on Amazon →HVAC Sizing Formulas & Guide
How We Calculate Loads
Running Watts Formula
(Capacity_BTU / SEER) + Fan_Watts
Example: A 3-Ton (36,000 BTU) 13 SEER unit:
(36,000 / 13) + 500 = ~3,269 Watts
Starting Surge Formula
Running_Watts × Surge_Factor
- Standard AC: ~3.5x to 5x running watts
- With Soft Start: ~1.5x running watts
- Electric Furnace: 1.0x (No Surge) + Fan Surge
Typical AC Wattage Reference (13 SEER)
| Size | Running Watts | Standard Start | Soft Start |
|---|---|---|---|
| 1.5 Ton | ~1,900 W | ~5,700 W | ~2,800 W |
| 2.0 Ton | ~2,400 W | ~7,200 W | ~3,600 W |
| 3.0 Ton | ~3,300 W | ~10,000 W | ~5,000 W |
| 4.0 Ton | ~4,200 W | ~14,000 W | ~6,300 W |
| 5.0 Ton | ~5,100 W | ~17,000 W | ~7,600 W |
*Estimates vary by age, brand, and temperature.