Generator Sizing for Central Air: Tons, Surge Watts, and Soft-Start Kits
A/C generator sizing: watts by tonnage, the compressor surge explained, soft-start kits, and heat pump notes.
Air conditioning is the reason home generators are the size they are: the compressor's starting surge dwarfs every other household load. Here's the tonnage-to-watts table, the soft-start trick that can save a size class, and the heat-pump wrinkle.
The tonnage table
Running / starting watts, roughly: 2-ton: 2,800 / 7,000W. 3-ton: 3,500 / 9,800W. 4-ton: 4,500 / 12,500W. 5-ton: 5,500 / 15,000W. The starting figure lasts a second or two, but the generator must supply it or trip: it's the single most important number in residential sizing.
Soft-start kits: the honest take
A soft-start module ramps the compressor instead of slamming it, cutting the surge 40 to 60%: often enough to drop a generator size class or let a battery system start the A/C at all. They cost a few hundred dollars installed, work on most units, and we spec them routinely: one of the few genuine free lunches in this field.
Heat pumps and dual systems
Heat pumps surge like A/C year-round (they're the same compressor) and add backup-heat strips that can be brutal electric loads: tell us the strip kilowatts. Dual systems: see load management, the standard answer so both can't surge at once. Variable-speed inverters barely surge at all: if you're replacing HVAC soon, say so; it changes the generator quote.
Quick Answers
What size generator runs a 4-ton A/C?
With household base load: the 22 to 26kW class, or smaller with a soft-start kit. The surge plus everything-else math decides it precisely.
Do soft-start kits void HVAC warranties?
Reputable kits installed by licensed technicians generally don't, and several HVAC makers now factory-offer them: confirm per your unit, and we'll flag it in the quote.
Can a Powerwall start central air?
Often yes with a soft-start kit and appropriate battery count: it's a standard design pattern now for battery whole-home backup.