Generator size by appliance / central air
What size generator runs central air conditioning
Central air conditioner, 24,000 BTU (2 ton): 3,800 W running plus 4,950 W more for a few seconds as it starts, so a generator needs at least 8,750 W of starting capacity to run it on its own. The smallest of the six portables this site covers that can do it is the Champion 201040 (7,500 W running, 9,375 W starting).
Generac's brochure lists a 24,000 BTU (2 ton) central air conditioner at 3,800 W running and 4,950 W additional starting. Generac's standby sizing page gives a much higher starting figure for a 3 ton system: up to 15 to 18 kW to start.
Central air is a 240-volt load wired into the panel, so a portable can only feed it through a transfer switch or interlock installed by an electrician.
Soft starters fitted to the compressor cut the start current; Micro-Air states up to a 75% reduction for its EasyStart Flex. The calculator does not apply any reduction, because it varies by unit.
The figures and where they come from
| Device | Source | Running W | Additional starting W | Starting need alone |
|---|---|---|---|---|
| Central air conditioner, 24,000 BTU (2 ton) | Generac GP brochure (2023) | 3,800 | 4,950 | 8,750 |
Highlighted rows are the figures the calculator uses. Every table here prints additional starting watts: the surge on top of running watts.
Which portables can run it
| Generator | Running / peak W | Alone | With fridge, 6 LED bulbs, 2 chargers |
|---|---|---|---|
| Honda EU2200i | 1,800 / 2,200 | No | No |
| Honda EU3000iS | 2,800 / 3,000 | No | No |
| Westinghouse iGen5000 | 3,900 / 5,000 | No | No |
| Honda EU7000iS | 5,500 / 7,000 | No | No |
| Champion 201040 | 7,500 / 9,375 | Yes | No |
| Westinghouse WGen9500DF | 9,500 / 12,500 | Yes | Yes |
A generator fits when its running rating covers every running watt and its peak (or "max") rating covers the running total plus the single biggest starting surge. Adding the basics — a refrigerator (700 W running, 2,200 W to start), six 15 W LED bulbs and two phone chargers — raises the running load to 4,630 W and the starting need to 9,580 W. The smallest portable here that covers that is the Westinghouse WGen9500DF.
On a standby generator
A home standby unit is rated in kilowatts and has no overload capacity: Generac's rating definition says "No overload capability is available for this rating." Using Generac's own formula — sum of running watts plus the highest single starting burst — the central air with the basics needs 9.6 kW. The smallest Guardian model that covers it on natural gas is the 14 kW, rated 14 kW on natural gas and 14 kW on propane, which leaves 4.4 kW of starting room for everything else. Whole-home lists are on the standby generator pages.
Before running anything, read the carbon monoxide distance rules and how a transfer switch keeps power off the utility lines. Other appliances: refrigerator · sump pump · well pump · furnace · window AC · heat pump · space heater · water heater · washing machine · garage door opener · CPAP · oxygen concentrator.