Whole house generators, explained plainly
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Quick answer
A whole house generator, also called a home standby generator, sits outside like a central air unit. It runs on natural gas or propane and connects through an automatic transfer switch, so it can start supplying power seconds after an outage begins. Generac says smaller homes may need 10 to 18 kW, and larger homes with several air conditioners may need 22 to 28 kW. Size by your actual electrical load, not square footage. Plan on professional installation, a permit and an inspection.
How a standby generator differs from a portable one
A portable generator is something you wheel out, start and plug things into. A standby generator stays in place. Generac describes its home standby units as installed outside the home like a central air conditioner and running on natural gas or liquid propane. They connect to the home's wiring through an automatic transfer switch, and can start supplying power seconds after an outage begins.
The transfer switch is the key part. It keeps generator power and utility power apart, so you never feed power back onto the lines. NFPA's generator safety sheet says any connection to house wiring needs a properly rated transfer switch. A qualified electrician should install it to the National Electrical Code and local codes.
| Portable | Home standby | |
|---|---|---|
| Starts | By hand, when you get to it | Automatically, seconds after an outage |
| Fuel | Gasoline, often propane too | Natural gas or propane supply |
| Coverage | What you plug in, or a few circuits | Essential circuits or the whole home |
| Install | Cords; transfer switch optional | Pad, fuel line, transfer switch, permit |
What size whole house generator you need
Generac's sizing guide puts it plainly: match the generator to your peak electrical load, not your square footage. Its published ranges give a starting point:
- About 1,550 sq ft: 10 to 14 kW can prioritize the air conditioner and well pump. 18 kW may be safer if the home relies on an electric heat pump or high-draw medical equipment.
- About 2,000 sq ft: Generac calls 18 to 22 kW the sweet spot, and says a 2,000 sq ft house typically needs 20 or 22 kW for whole-home coverage.
- Larger homes or several AC units: 22 to 28 kW.
These are a maker's ranges, so have an electrician do a load calculation on your actual panel before you buy. Big loads like central air, electric water heaters, ranges and well pumps drive the size more than floor area.
Essential circuits or the whole home
You do not have to back up everything. Generac describes two levels:
- Essential circuits: refrigerator, lighting, well pump and a handful of critical outlets. For example, Generac's 14 kW Guardian bundle (model 7224) pairs the generator with a 16-circuit transfer switch for essential-circuit protection, rated 14 kW on both propane and natural gas.
- Whole home: HVAC, kitchen appliances and high-draw systems keep running with minimal interruption. This needs a larger unit and a service-rated switch.
Essential-circuit setups use a smaller generator and a simpler switch. Whole-home setups mean you never have to think about what is on.
Natural gas vs propane ratings
Standby generators usually list two outputs, one per fuel, and the natural gas figure is lower. Generac's 26 kW bundle (model 7328) is rated 26 kW on liquid propane and 24 kW on natural gas. If your home has a gas line, size from the natural gas rating, not the headline number.
Propane homes need a tank big enough to run the generator for the length of outage you plan for. Ask your installer and propane supplier to size it together.
What installation involves
Generac's guide says professional installation is required, and that most jurisdictions require an electrical permit and an inspection. Expect these steps:
- A load calculation and site check: placement, clearances and noise.
- A pad, the generator, and a gas line from your meter or propane tank.
- A transfer switch wired into your panel: automatic for standby units.
- A permit, inspection and start-up check.
After that, upkeep matters. Generac says to check oil and add it if needed every 24 hours of use during an outage, and to follow the maker's maintenance schedule. Its standby units carry a 5-year limited warranty.
If a standby unit is more than you need
Many homes do fine with a portable generator and a manual transfer switch for a few chosen circuits. Generac says its HomeLink manual transfer switches power hardwired appliances such as a gas furnace, well pump and electric water heater, and it recommends installation by an electrician. See our guide to a generator for your house and our transfer switch guide to compare.
What to look for when you buy
Air-cooled home standby generator, 10 to 18 kW, with essential-circuit transfer switch
Best for: Smaller homes backing up the fridge, lights, well pump and furnace or one AC
Generac puts most 1,550 sq ft homes at 10 to 18 kW. Its 14 kW Guardian bundle comes with a 16-circuit transfer switch for essential circuits, which keeps the job simpler.
Watch out: Covers chosen circuits only. Confirm big loads like central air fit before you buy.
See options on Amazon (opens Amazon in a new tab)22 kW class standby generator with 200 amp automatic transfer switch
Best for: About 2,000 sq ft homes wanting whole-home coverage
Generac says a 2,000 sq ft home typically needs 20 or 22 kW for whole-home coverage, and calls 22 kW the standard for that range.
Watch out: Natural gas output is lower than the propane rating. Size from the fuel you actually have.
See options on Amazon (opens Amazon in a new tab)24 to 28 kW standby generator
Best for: Larger homes with several air conditioners or high electrical demand
Generac's guidance for larger, high-demand homes is 22 to 28 kW. Its 26 kW unit is rated 26 kW on propane and 24 kW on natural gas.
Watch out: Needs a gas supply that can feed it. Your installer must check meter and line capacity.
See options on Amazon (opens Amazon in a new tab)Manual transfer switch for a portable generator
Best for: Homes that only need a few circuits and already own a portable
A manual transfer switch lets a portable generator feed chosen circuits safely. NFPA says house connections need a properly rated transfer switch.
Watch out: Have a qualified electrician install it to code. You still start the generator yourself.
See options on Amazon (opens Amazon in a new tab)Questions people ask
- What size whole house generator do I need?
- Generac says to size by load, not square footage. It suggests 10 to 18 kW for smaller homes, 20 or 22 kW for whole-home coverage of about 2,000 sq ft, and 22 to 28 kW for larger homes with several AC units.
- How does a Generac standby generator work?
- Generac says its standby units sit outside like a central air unit, run on natural gas or propane, and connect through an automatic transfer switch that starts supplying power seconds after an outage begins.
- How fast does a whole house generator turn on?
- With an automatic transfer switch, Generac says its standby units can start supplying power seconds after an outage begins.
- Can I install a whole house generator myself?
- Generac's guide says professional installation is required, and most jurisdictions require an electrical permit and an inspection.
- Is natural gas or propane better for a standby generator?
- Use the fuel your home already has. Natural gas ratings run lower: Generac's 26 kW model is 26 kW on propane and 24 kW on natural gas.
Sources
- Home Generators for Backup Power & Peace of Mind, Generac
- What Size Generator Do I Need? Sizing Guide, Generac
- Home Standby Generator, 26kW, Transfer Switch Bundle (7328), Generac
- 14kW Guardian Series Home Generator with Transfer Switch (7224), Generac
- HomeLink Manual Transfer Switches, Generac
- Generator Safety tip sheet, National Fire Protection Association