Generator sizing starts with the loads the home must carry during an outage, not with the cabinet size that looks familiar. The cited sources here separate essential-circuit backup, whole-home standby sizing, starting surge, square-footage ranges, and the point where air-cooled equipment gives way to liquid-cooled equipment.
Start with the loads that must run
Generac frames a 10 kW generator as an essentials-level answer, covering a refrigerator, lighting, a well pump, and a handful of critical outlets. That is a narrower job than whole-home protection. Generac also describes 22 kW as the industry standard for whole-home protection on about 2,000 sq ft homes. Those figures define the planning contrast: an essentials load can be much smaller than a whole-home load, and the right size depends on which circuits must stay available.
The key is to decide whether the goal is essential backup or broader whole-home coverage before using any square-footage shortcut. A home that only needs refrigeration, lighting, well pump power, and critical outlets can be evaluated differently from a home where the owner expects the central cooling system and larger loads to operate. The cited 10 kW and 22 kW examples are not universal prescriptions. They are reference points from Generac for different backup expectations.
Account for starting wattage
Generac's load calculation rule is direct: total kW equals the sum of running wattages plus the highest single starting wattage burst. The reason is motor starting load. Generac notes that motor starting wattage is often 2-3x the running figure. The air-conditioning example makes the effect visible: a 3-ton AC may run at 3.5-5 kW, but can require up to 15-18 kW for starting.
That starting surge can dominate the sizing conversation. A generator that appears large enough by running watts can still be undersized if the largest motor load is ignored. Norwall gives a related sizing method: add running watts, then add 25% to prevent overload, then add the largest starting watts. That approach keeps running load, overload margin, and starting burst separate instead of burying them inside a vague whole-home estimate.
Use square-footage ranges only as retailer-sourced screening
Portlandia Electric Supply provides square-footage sizing ranges, and those should be treated as retailer-sourced screening values. For 1,000-1,500 sq ft homes, the retailer source lists 10-14 kW, with 14 kW covering AC start on single-compressor homes. For 2,000-3,000 sq ft homes, the same retailer source lists 18-22 kW and says 22 kW is the volume seller.
Those ranges are useful for spotting whether a quote is in a plausible neighborhood, but they are not a substitute for a load calculation. The same square footage can carry different loads depending on which circuits are backed up and which motor loads need to start. Use the retailer-sourced ranges as a quick screen, then require the installer to show the running-wattage total and the largest starting burst. The cited Generac and Norwall methods give a clearer basis for final sizing than square footage alone.
Know where air-cooled sizing tops out
The retailer-sourced sizing guide identifies 26 kW as the top air-cooled tier and says homes above that level step to liquid-cooled equipment. That does not mean every home near that size should automatically use the largest air-cooled unit. It means the equipment category has a cited upper tier, and sizing beyond that moves into a different system type.
For a quote review, ask the installer to show why the selected size lands below, at, or above the air-cooled threshold. If the design relies on a 22 kW whole-home reference, compare it with Generac's note that 22 kW is the industry standard for whole-home protection on about 2,000 sq ft homes. If the project is being pushed toward the top air-cooled tier, compare it with the retailer-sourced 26 kW upper tier. If the calculated load exceeds that tier, the liquid-cooled discussion is no longer just an upsell claim; it follows the cited sizing category boundary.
What the sizing proposal should show
A useful sizing proposal should make the load math visible. Generac's formula says total kW equals the sum of running wattages plus the highest single starting wattage burst. Norwall's method adds another guardrail: add running watts, then add 25% to prevent overload, then add the largest starting watts. Those statements give the homeowner a clear way to ask for the calculation instead of accepting a label on a brochure.
The proposal should also identify whether square-footage guidance was used only as a screen. Portlandia Electric Supply's 1,000-1,500 sq ft and 2,000-3,000 sq ft ranges are retailer-sourced, so they should not be presented as the final engineering answer. If the quote lands near the 26 kW top air-cooled tier, ask whether the actual load calculation stays within that category or whether the project is being moved into liquid-cooled sizing for a documented load reason.
That request also keeps square-footage screening from becoming the only sizing basis. The final proposal should connect the named circuits, the expected motor loads, and the selected fuel rating so the homeowner can see why the recommended cabinet size matches the outage plan.
Frequently asked questions
What size generator covers essential circuits?
Generac says 10 kW covers a refrigerator, lighting, a well pump, and a handful of critical outlets.
What size is commonly used for whole-home protection?
Generac describes 22 kW as the industry standard for whole-home protection on about 2,000 sq ft homes.
How should starting wattage be handled?
Generac says total kW equals the sum of running wattages plus the highest single starting wattage burst, and that motor starting wattage is often 2-3x the running figure.
Why does central AC affect generator size?
Generac gives a 3-ton AC example: 3.5-5 kW running, but up to 15-18 kW starting.
Are square-footage sizing charts enough?
Use them only as retailer-sourced screening. Portlandia Electric Supply lists 1,000-1,500 sq ft homes at 10-14 kW and 2,000-3,000 sq ft homes at 18-22 kW, but final sizing should still account for running watts and starting surge.