Buying guide · Generators

How to Size a Standby Generator

Undersized trips. Oversized wastes. Sized right disappears.

Generator sizing is a load calculation, not a brochure choice. An undersized unit trips the moment the AC compressor kicks in during dinner; an oversized one costs more to buy, fuel, and maintain forever. Here’s the method — the same one we run under TECL #35881 before recommending any unit. Figures below are illustrative; your answer comes from your own panel and meter.

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The method

Six steps to the right unit.

1
Decide what it must carry
Whole-home means everything, sized for your worst summer hour. Essentials means a chosen circuit set — refrigeration, lights, internet, some HVAC — behind a transfer switch that manages the rest.
2
Count running watts
Every load you’ll carry, added at its steady draw. Your electric bill and panel schedule are the honest sources — a home’s real simultaneous draw is usually far below the sum of every breaker.
3
Respect starting loads
Motors — AC compressors, well pumps, pool equipment — briefly draw several times their running watts at startup. This surge, not the steady state, is what trips undersized generators. Load-management modules can stagger big starters; that’s a design decision, not an accessory.
4
Check your fuel supply
A natural-gas unit is only as strong as the meter and line feeding it — capacity must cover the generator plus your furnace and water heater on a winter morning. On propane, runtime is the tank, so duration risk sets its size.
5
Site it to code
Clearances from windows, doors, and openings; property-line setbacks; sound considerations for you and the neighbors. Placement can change the install cost more than the unit choice does.
6
Get the load calc done right
Steps 1–5 are exactly what a licensed electrical contractor verifies on-site. We’re Generac-certified on the current standby line, and the calculation — panel, meter, gas, placement — is part of how we quote.
The money question

Essentials vs whole-home.

Most households discover their must-run list fits a mid-size unit — and that the jump to whole-home is driven almost entirely by air conditioning. That’s not a reason to skip AC coverage (this is Texas); it’s the reason the load calc comes before the checkout page. Weighing a battery instead — or as well? The comparison.

Asked often

Generator sizing, answered.

What size does a typical house need?

There’s a reason we won’t answer that in a vacuum — “typical” hides the AC tonnage, well pumps, and gas capacity that decide it. The load calc answers it for your house, definitively.

Natural gas or propane?

If you have gas service with capacity to spare, natural gas — indefinite runtime, no tank. No gas service? Propane works well; the tank becomes part of the sizing conversation.

Can a generator and a battery share the job?

Yes — battery for instant, silent switchover; generator for the long haul. We design hybrids, and both halves are in-house.

What’s involved in installation?

Permit, pad, transfer switch, fuel hookup, inspection, and commissioning — the full path is here, all performed under TECL #35881.

When the grid quits, sized right just hums.

One load calculation stands between you and the right unit.
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