Electrical guide
Generator sizing goes wrong in both directions. Undersized units stall and reset when the air conditioner starts. Oversized units cost thousands more than necessary and run inefficiently at light load. The answer comes from measuring, not from square footage rules of thumb.
Essential circuits. Fridge, freezer, well pump, furnace blower, some lights and outlets, internet. Runs on a smaller unit and a sub panel. Usually 8 to 12 kW.
Whole home. Everything, including central air. For a typical Alabama home with one AC unit, 14 to 18 kW. Larger homes with two air conditioners generally need 22 to 26 kW.
An air conditioner compressor draws several times its running current for the first second or two. A well pump does the same. Generator sizing is driven by that inrush, not by steady-state draw, which is why two homes with identical square footage can need different units. Soft starters on the AC compressor can sometimes let you drop a whole size class, which is often cheaper than the bigger generator.
An automatic transfer switch senses the outage, starts the generator, disconnects the utility and connects the house — usually in under thirty seconds. Just as importantly, it makes it physically impossible for generator power to backfeed onto the utility line, which is a lethal hazard for crews working to restore power. Running a generator through a dryer outlet is not a shortcut, it is a serious danger.
Electrical installation for a whole home system typically runs $5,500 to $12,000, plus the generator and the gas work. The electrical portion is one to two days; fuel supply and utility coordination usually set the schedule. Book before storm season, not during it — lead times stretch badly once the forecast turns.
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