Cooling is usually one of the largest electric lines in a warm-climate home. The number is not “the AC is on.” It is how many watts the unit draws, how many hours it runs, and how hard the compressor works for the outdoor temperature you actually have.
A small window unit cooling one room is a different machine from a central system that cools the whole house. Window and portable units often sit around 500–1,500 watts. A typical central system can be 2,200–5,200 watts at the air handler and outdoor unit together while the compressor is running. Runtime is the other half: eight hours on a mild day is not twelve hours in a heat wave.
What changes the bill is rarely a myth about “starting surge.” It is thermostat setpoint, a dirty filter, sun through glass, a window left cracked, and insulation. Two degrees cooler is not a comfort rounding error — the system usually runs longer for the same house.
Whatt starts many AC cards near 1,000 watts (a typical window unit) and about 8 hours, then lets you pick window vs central and how big the house is. Duty cycle matters: the compressor is not at full power every minute the system is “on.”
At 18.8¢ per kWh, a 1,000-watt window unit running 8 hours is about 1.50 that day (8 kWh × 18.8¢). A 3,200-watt central system on a long hot day is several times that. Those are usage estimates, not the whole electric bill.
How to tell what you have
A window unit sits in one opening and cools one room. A portable unit has a vent hose. Central is an outdoor condenser plus ducts. Mini-splits are wall heads with their own outdoor unit — use that card, not this one.
What people mix up
The “kick” when the compressor starts is not hours of extra kWh. Runtime and outdoor temperature are. A dirty filter and a setpoint two degrees colder both lengthen that runtime.
Related
Usage estimate only — not a utility bill, load calc, or advice.