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Most homes end up somewhere between about 14 and 24 kW. Smaller homes with gas appliances, or anyone backing up only essential circuits, often fit 10 to 14 kW. All-electric homes and large homes with more than one air conditioner can need 24 kW and up, or load management to stay smaller. The right answer comes from your loads, not a rule of thumb.
Common sizes compared
| Size | Typical fit |
|---|---|
| 10 to 14 kW | Smaller homes with gas appliances, or essential circuits only |
| 14 to 22 kW | Most homes with gas heat and one or two air conditioners, often with load management |
| 24 to 26 kW | All-electric homes, large homes, or several big air conditioners |
| Above about 26 kW | Usually liquid-cooled units for very large loads |
Rough bands only. A written load calculation sets the real number.
Whole-house or essential circuits
Whole-house setups use a service-rated transfer switch that moves the entire panel to the generator. You need enough capacity for what you’ll realistically run together. Load management shuts off big loads when needed.
Essential-circuit setups move a chosen subpanel only, such as the fridge, furnace, lights, sump and some outlets. That allows a smaller generator but limits what works during an outage.
Three ways to size, from rough to right
- Square footage charts. Fine for a first budget, unreliable for buying.
- Your appliance list. Add the running loads you want covered and the largest starting surge. The wattage calculator helps for a first pass.
- A professional load calculation. The installer reviews your panel, data plates and sometimes your utility demand data. This is the one to buy on.
Two quotes compared
A gas-heated home with a 4 ton central AC gets two quotes. Quote A is a 24 kW whole-house unit with no load management. Quote B is an 18 kW unit with a smart transfer switch that sheds the AC for a few seconds while the well pump starts, plus a soft starter on the AC. Both cover the home’s realistic peak. Quote B costs less, burns less fuel at light load and is quieter. Quote A has more headroom if the owner adds an EV charger or a hot tub later. Neither is wrong. It depends on budget and future plans.
Natural gas vs propane output
Generators make less power on natural gas than on propane. Generac’s spec sheet for the 22 kW Guardian, for example, rates it at 22,000 watts on LP but 19,500 watts on natural gas. If you’re on natural gas, size against the NG rating.
Fuel supply has to keep up
The gas line and meter, or the propane tank and regulator, must deliver the full-load fuel flow. Generac notes that fuel pipe must be sized for full load and lists the inlet pressure its units need. An undersized line can cause the generator to stumble when a big load starts.
Cost by size
Larger generators cost more, but installation costs don’t scale as much, so stepping up one size is often a modest share of the total. The bigger cost driver is usually site work: gas line length, electrical service changes and the pad.
Air-cooled or liquid-cooled?
Air-cooled engines power most home standby units up to roughly 26 kW. Liquid-cooled models, usually above that, suit very large homes, long run times and heavy loads. They cost more and need more maintenance.
Most oversized or undersized installs trace back to one of these:
- Sizing for every appliance running at once. That rarely happens. Load management is cheaper than a much bigger generator.
- Undersizing for air conditioning. A central AC’s starting surge is often the deciding factor. Soft starters help.
- Forgetting future plans like an EV charger, a heat pump conversion or an addition.
- Ignoring noise rules. Some towns limit generator noise or require setbacks from property lines.
Leave the final size to a licensed installer. Ask for the load calculation in writing, and ask whether load management is included.
Standby size questions
Is 22 kW enough for a whole house?
For many homes with gas heat and one or two AC units, yes, especially with load management.
Liquid-cooled or air-cooled?
Air-cooled units cover most homes. Liquid-cooled models are for larger loads and longer run times.
Does a bigger generator use more fuel at the same load?
Usually a little more at light loads, because a bigger engine has higher idle consumption. Check the spec sheets’ half-load figures for both sizes.
The step-by-step method is in how to size a standby generator properly. A worked example is in sizing for a 2,400 sq ft home. Fuel planning is in propane use.
Where I’d expect most homes to land
For a typical home with gas heat and one or two air conditioners, a 20 to 24 kW unit, or a smaller one with load management, is a common result. Go smaller if you’re only backing up essential circuits. Go bigger, or add load management, if the house is all-electric or has several large motor loads. Whatever a brochure suggests, the final number should come from a written load calculation.
