What Size Generator Do You Need for Central Air Conditioning?
Central air is usually the single biggest load in a house, and its compressor has a large starting surge on a 240-volt circuit. A soft-start kit on the outdoor unit can cut that surge by about half, often dropping you a full generator size.
| Appliance | Running / starting W | On its own | With fridge, lights and Wi-Fi | Soft-start kit, with fridge, lights and Wi-Fi |
|---|---|---|---|---|
| Central AC or heat pump (2 ton) | 2,000 / 6,000 | 6,500-watt 10 kW standby | 7,500-watt 10 kW standby | 5,000-watt 10 kW standby |
| Central AC or heat pump (3 ton) | 3,200 / 9,500 | 9,500-watt 14 kW standby | 12,000-watt 14 kW standby | 6,500-watt 10 kW standby |
| Central AC or heat pump (4 ton) | 4,300 / 12,500 | 15,000-watt 14 kW standby | 15,000-watt 18 kW standby | 7,500-watt 10 kW standby |
| Central AC or heat pump (5 ton) | 5,300 / 15,500 | none (too big for a portable) 18 kW standby | none (too big for a portable) 18 kW standby | 9,500-watt 14 kW standby |
Smallest portable (by starting watts) and smallest standby generator on natural gas, keeping about 20% headroom.
Tips
- Find the tonnage on the outdoor unit's model number: the digits 24, 36, 48 or 60 usually mean 2, 3, 4 or 5 tons.
- Ask an HVAC technician about a soft-start kit, typically $300–$500 installed.
- Heat pumps size the same way as AC in cooling mode, but backup electric heat strips can add 5–10 kW; keep those off the generator.
See also the appliance wattage chart and what each generator size can run.