What Size Whole-Home Generator Do You Need?

By David Fish, Owner & Lead Technician, TX Lic. TACLB99535E · Last updated July 2026

The size of generator you need is determined by two numbers: the running load of everything you want powered at once, and the startup surge of the largest motor on that list — which in a Texas home is almost always the air conditioner. A generator that carries your running load but cannot absorb the AC compressor’s inrush will stall or drop the AC at exactly the moment you need it, so sizing is a load-math exercise, not a guess off square footage.

What loads actually go into the calculation?

Start with a circuit-by-circuit inventory, sorted into three buckets. Essentials: refrigerator and freezer, some lighting, internet, garage door, medical equipment. Comfort: the HVAC system — in our climate this is not optional in any serious plan, because a July outage without AC makes the house unlivable within hours. Convenience: ovens, dryers, pool equipment, EV charging, a second HVAC system. Each item has a running wattage; motors and compressors also have a starting surge several times their running draw. The generator must handle the sum of everything running plus the largest single surge on top.

Why does the AC dominate generator sizing in Texas?

Because compressor inrush is the biggest single electrical event in the house. A central AC drawing modest power once running can demand several times that for the moment of startup, and if the generator cannot supply it, the compressor fails to start — repeatedly, which is hard on both machines. Two design tools shrink the problem: soft-start kits on the AC, which electronically ease the compressor up instead of slamming it on and can meaningfully reduce the required generator size; and load-management modules, which stagger big loads so the dryer and the second AC never demand startup power simultaneously. Homes with two or three systems — typical for the 4,000-plus square foot properties we serve in Southlake and Westlake — almost always justify load management over brute-force generator capacity. If you are also weighing what kind of HVAC to pair with backup power, note that equipment choice changes the load profile — see heat pump vs. AC + furnace in North Texas.

Whole-home versus essential-circuits: which approach fits?

True whole-home coverage backs every breaker in the panel and is the right call when the budget allows and the property runs multiple HVAC systems, refrigeration, and gates or wells that all matter during an outage. An essential-circuits setup backs a curated subpanel — smaller generator, lower cost, and honest coverage of what you actually decided matters. The failure modes live at the extremes: undersizing to save money, then discovering during an ice storm that the heat cannot run while the kitchen is live; and oversizing "to be safe", which wastes capital and runs the engine inefficiently at light load. Fuel supply is the third trap — a correctly sized generator on an undersized natural gas line starves under load, so the gas meter and line sizing are part of the design, not an afterthought.

How does sizing interact with fuel consumption and runtime?

Bigger generators burn more fuel at every load level, which matters during a multi-day event: a right-sized unit with load management sips its natural gas supply, while an oversized one pays a standing fuel penalty for capacity it rarely touches. On propane systems the math is sharper still, because the tank is finite — sizing conservatively and managing loads is the difference between a tank that outlasts the outage and one that does not. This is also why the sizing conversation should include how you actually live during an outage: powering everything as if nothing happened is one valid answer, but many families are happy with cool air, cold food, lights, and internet — a materially smaller machine.

What does a real sizing engagement look like?

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What is the next step?

Get a site assessment that inventories your panel, measures the AC surge, and sizes the gas supply — the three things a square-footage chart cannot see. Our Whole-Home Generators team runs that assessment across the area, including whole-home generators in Southlake, TX and whole-home generators in Keller, TX. If you want the operating principles first, start with how whole-home generators work — and when you are ready to structure the investment, how GoodLeap HVAC financing works covers the payment mechanics.