How to Choose a Standby Generator

Choosing a standby generator is easier when the decision is handled in order: decide what the home must power, size the load, choose air-cooled or liquid-cooled equipment, check the fuel rating, then compare installed cost tiers. The facts below are limited to cited generator sources and planning ranges.

Start with backup scope

The earliest decision is whether the goal is essential-circuit backup or whole-home backup. Generac frames a 10 kW generator as an essentials-level setup that covers a refrigerator, lighting, a well pump, and a handful of critical outlets. Consumer Reports gives a separate whole-house threshold, saying whole-house backup essentially needs 15,000W or more to power all appliances. Generac also describes 22 kW as the industry standard for whole-home protection on about 2,000 sq ft homes.

Those numbers describe different backup promises. Ferguson, an industry source, describes the switching distinction clearly: a whole-house switch powers the entire main panel, while an essential or load-center switch energizes only 8 to 16 critical circuits. Treat that switch choice as part of the generator decision.

Size the load before trusting square footage

Generac's sizing formula is the cleanest starting point: total kW equals the sum of running wattages plus the highest single starting wattage burst. Motor starting wattage is often 2-3x the running figure. Generac's air-conditioning example shows the gap: a 3-ton AC may run at 3.5-5 kW, but can require up to 15-18 kW to start. Norwall gives a related method: add running watts, then add 25% to prevent overload, then add the largest starting watts.

Square-footage charts can still be useful as a screening check, but they should be attributed as retailer-sourced. Portlandia Electric Supply lists 1,000-1,500 sq ft homes at 10-14 kW, with 14 kW covering AC start on single-compressor homes. The same retailer source lists 2,000-3,000 sq ft homes at 18-22 kW and says 22 kW is the volume seller. Those ranges can flag a mismatched quote, but final sizing should still show running loads and the largest starting burst.

Choose air-cooled or liquid-cooled equipment

Norwall describes air-cooled standby generators as ranging from 7.5 kW to 26 kW. It also says air-cooled units fit moderate or cool climates under 100F, average homes, and tight installs. Portlandia Electric Supply, a retailer source, identifies 26 kW as the top air-cooled tier and says homes above that step to liquid-cooled equipment.

Liquid-cooled equipment is the next category when capacity, climate, or reliability expectations exceed the air-cooled fit. Norwall says liquid-cooled starts at 15 kW for diesel and 22 kW for natural gas or propane. Norwall also says liquid-cooled equipment fits hot desert climates 120F+, large homes, and higher reliability needs.

Check fuel rating and installed cost together

Fuel choice can change actual output. Briggs and Stratton lists propane at about 2,516 BTU/cu ft and natural gas at about 1,030 BTU/cu ft. Norwall says propane has higher usable energy content than natural gas and that natural gas may lower actual capacity. Generac gives a model-specific example: a 20kW unit is rated 17,000W on natural gas and 20,000W on liquid propane. Norwall gives another air-cooled example, listing a Generac 22kW unit at 19.5 kW on natural gas and 22 kW on propane.

The budget also has to match the selected size class. Per a cost-aggregator, installed standby ranges are $9,600-$16,900 installed for 8 kW standby, $11,200-$19,500 installed for 14 kW standby, and $13,400-$23,300 installed for 22 kW standby. The same cost-aggregator lists $21,000-$36,700 installed for liquid-cooled 25 kW+ equipment, and says installed range includes the unit, ATS, gas-line/wiring run, pad, and permit. Compare bids only after the size, fuel rating, and included scope are clear.