20 kW Generator
A 20 kW standby generator is a common mid-range choice for whole-home backup — often considered for mid-size homes and may support central AC, appliances, and lighting depending on connected loads and starting current.
Quick Answer
A 20 kW standby generator can cover most mid-size homes (roughly 1,500–2,500 sq ft with moderate electrical loads), including central AC in many configurations, a refrigerator, lights, furnace blower, and typical appliances. Homes with large central AC systems (3.5+ tons), electric resistance heat, or multiple major loads running simultaneously may need 22–24 kW for reliable headroom. A load calculation determines fit more accurately than square footage.
Coverage depends on simultaneous demand and starting surges — a load calculation using your actual appliances is required to confirm.
A 20 kW generator may support most 2–3 ton central AC systems when other loads are typical, but actual coverage depends on the unit's starting surge characteristics and what else is running simultaneously. For a 3.5-ton or larger AC system, the starting surge may approach the generator's capacity limit — a load management module or stepping up to 22 kW is worth discussing with an installer. The distinction between 20 kW and 22 kW often comes down to the specific AC equipment in the home.
Natural gas consumption at 20 kW under 50% load runs approximately 2.0–2.5 cubic feet per kilowatt-hour. On propane at 50% load, expect roughly 1.3–1.7 gallons per hour — a 500-gallon propane tank provides approximately 5–7 days at that rate. Verify with manufacturer documentation for the specific model.
20 kW units are widely available from all major residential brands. Pad size, clearance requirements, and transfer switch installation follow the same process as other residential sizes — confirm the specific model's installation footprint and clearance requirements before selecting a placement. Lead times for equipment and permits vary by market.
A 20 kW generator draws approximately 83 amps at full output on 240V. A 200-amp service panel typically accommodates this without upgrades. Some 100-amp service installations can support a 20 kW generator depending on the overall load profile, but a panel assessment is important.
Verify sizing with your actual loads
The Generator Size Calculator and Electrical Load Worksheet give you a more accurate result than any size-based rule of thumb.
