What size generator to run a house
The size a house needs comes down to floor area, cooling and fuel. Answer the three questions about your own home.
Work out the right size for your house
Fine-tune the load sheet
Circuits on the generator
| Line | Basis | Watts |
|---|
Next: cost by state models and prices propane tank hours transfer switch
US average prices, a 2,000 sq ft home, natural gas and a 3-ton AC:
Sizing by square footage
| House | Running load | No central air | Central AC, natural gas | Central AC, propane | Heat pump, natural gas |
|---|---|---|---|---|---|
| 1,000 sq ft, 2 ton | 10.8 kW | 14 kW | 18 kW | 14 kW | 24 kW |
| 1,200 sq ft, 2 ton | 11.3 kW | 14 kW | 18 kW | 18 kW | 24 kW |
| 1,500 sq ft, 3 ton | 12.7 kW | 14 kW | 18 kW | 18 kW | 26 kW |
| 1,800 sq ft, 3 ton | 13.1 kW | 14 kW | 22 kW | 18 kW | 26 kW |
| 2,000 sq ft, 3 ton | 13.3 kW | 14 kW | 22 kW | 18 kW | 26 kW |
| 2,500 sq ft, 3 ton | 13.9 kW | 18 kW | 22 kW | 18 kW | 32 kW |
| 3,000 sq ft, 4 ton | 16.0 kW | 18 kW | 24 kW | 22 kW | 32 kW |
| 3,500 sq ft, 4 ton | 16.6 kW | 18 kW | 24 kW | 22 kW | 32 kW |
| 4,000 sq ft, 4 ton | 17.2 kW | 18 kW | 26 kW | 22 kW | 32 kW |
| 5,000 sq ft, 4 ton | 18.4 kW | 22 kW | 26 kW | 24 kW | 38 kW |
The generator runs gas heat, kitchen and laundry appliances, plus an electric dryer. Size your home.
Pricing and fuel by size
Every size the table recommends is priced at US average rates. Generac posts a fuel table for every model. Each of the 38 kW, 26 kW, 18 kW and 24 kW units is rated to burn no more fuel in an hour than the next size down, so hourly fuel use doesn't climb in proportion to kW.
| Size | Installed, natural gas | Installed, propane | Gas an hour | Propane an hour | 250 gal tank | 500 gal tank | Fuel figures |
|---|---|---|---|---|---|---|---|
| 14 kW | $9,749 to $14,649 | $10,049 to $15,149 | $4.27 | $4.94 | 110 h | 221 h | Generac Guardian 14 kW |
| 18 kW | $10,569 to $15,469 | $10,869 to $15,969 | $3.70 | $4.64 | 118 h | 235 h | Generac Guardian 18 kW |
| 22 kW | $11,169 to $16,069 | $11,469 to $16,569 | $4.47 | $6.91 | 79 h | 158 h | Generac Guardian 22 kW |
| 24 kW | $11,589 to $16,489 | $11,889 to $16,989 | $4.45 | $6.91 | 79 h | 158 h | Generac Guardian 24 kW |
| 26 kW | $12,019 to $16,919 | $12,319 to $17,419 | $4.12 | $5.62 | 97 h | 194 h | Generac Guardian 26 kW |
| 32 kW | $21,600 to $27,500 | $21,900 to $28,000 | $5.66 | $9.28 | 59 h | 118 h | Generac XG03245 |
| 38 kW | $23,500 to $29,400 | $23,800 to $29,900 | $5.59 | $7.92 | 69 h | 138 h | Generac RG03824 |
An installed price covers Generac's list price including the switch, plus a permit, a fuel line, a pad and labor. The labor figure is based on the BLS electrician wage. This figure is an estimate for liquid-cooled 32 kW generators and larger. The propane price doesn't cover the cost of a tank. Half load figures come from Generac's fuel tables, using EIA US rates: $21.92 for each 1,000 ft³ and $2.73 for each gallon. Tanks are filled to 80%. Every price line.
How many watts a house uses
Not every circuit in a house runs at the same moment. Because of that, the load sheet counts the first 8,000 W in full and counts everything past that at 40%. Full weight applies to heating or cooling, plus one motor start. Take a 2,000 sq ft home fitted with a 3-ton AC: the running load reaches 13.3 kW, and 15.8 kW covers the moment the AC begins.
Find the appliance figures behind each line in the appliance wattage chart.
Your fuel choice between natural gas and propane changes the size.
On natural gas, an air-cooled standby engine makes about 11% less power than on propane. For a home of 2,000 sq ft, propane lets an 18 kW unit fit, while natural gas calls for 22 kW. See hourly fuel use for each size under generator fuel consumption. Propane tank hours appear under propane tank for a generator.
Questions about the size of a house
Which generator size is right for a 1,500 sq ft house?
With natural gas, 18 kW handles a 3-ton central AC, 14 kW works without central air.
How many watts does a house use?
With gas heat and a 3-ton central AC, a 2,000 sq ft home draws about 13.3 kW for the loads that tend to run together, reaching 15.8 kW in the second the AC starts.
What size generator handles just the essentials?
A fridge, freezer, 1/2 hp sump pump, microwave, lights, TV, fans and router together need about 4.6 kW to run. That load is handled by a 10 kW standby unit, or by a portable in the 5,000 to 7,500 watt range.