Why sizing matters more here than almost anywhere
Get the size wrong and you’ll feel it the first time the grid drops in August. Too small, and the generator strains — or trips — the moment your air conditioner tries to start. Too large, and you’ve spent thousands on capacity you’ll never use, plus higher fuel burn every hour it runs. In greater Houston, where the whole point of backup power is usually keeping the AC alive through brutal heat, sizing is the difference between a system that quietly carries your home and one that frustrates you for years.
A quick note before we dig in: we connect homeowners with one vetted, licensed local installer, and the real sizing number always comes from that installer’s site visit. What follows is how to think about it so you walk into that conversation informed.
kW, the number that matters
Standby generators are rated in kilowatts (kW) — how much electrical power they can supply at once. For residential air-cooled units you’ll commonly see ratings from around 10 kW up to roughly 26 kW; larger homes sometimes step up to liquid-cooled units of 30 kW and beyond. Your job isn’t to memorize ratings, it’s to match capacity to what your home actually draws when you need it most.
There are two broad philosophies, and the right one depends on your home and budget.
Whole-home coverage
A whole-home setup is sized to run essentially everything at once — every AC compressor, the electric range, the dryer, all of it — with margin to spare. It’s the simplest experience: an outage is nearly invisible. It’s also the most generator (and the most fuel and cost). For larger Sugar Land or Cypress homes with two or three AC systems, “whole-home” can mean a sizable liquid-cooled unit.
Managed power with load shedding
The smarter-money option for many homes is a more modestly sized generator paired with a load-management (load-shed) system. Smart switches in the panel prioritize what runs: your AC, kitchen, and key circuits get power, and lower-priority loads are momentarily dropped or rotated so the generator is never overwhelmed. You get the comfort that matters for thousands less in equipment. Many Houston installs land here, and for good reason.
The thing that catches people: AC startup surge
This is the Houston-specific trap. An air-conditioning compressor doesn’t just draw its running wattage — it pulls a brief startup surge (LRA, locked-rotor amps) several times higher than its steady draw at the instant it kicks on. A 4-ton system that runs at a few thousand watts can spike to a much larger number for a fraction of a second.
Now stack two or three AC units in a big house, all cycling on a 100°F afternoon, and you can see how a generator sized only for “running” loads gets blindsided. Proper sizing accounts for the largest motor’s surge landing on top of everything else already running. A soft-start device on the compressor can dramatically cut that surge and sometimes let you use a smaller generator — worth asking your installer about.
Don’t forget fuel de-rating
Generator nameplate ratings are usually given for natural gas, and the real delivered output depends on your fuel and conditions. Natural gas typically yields slightly less output than propane for the same engine, and supply-line pressure and pipe sizing matter — an undersized gas line can starve the unit under load. Heat and humidity (which Houston has in abundance) also nibble at output. A good installer factors this de-rating in rather than trusting the sticker number. The fuel choice itself is worth its own read: see natural gas vs. propane and the fuel overview on the hub.
A real load calculation beats any rule of thumb
You’ll see tidy rules online — “X square feet needs Y kW.” Ignore them. Two homes the same size can have wildly different electrical needs depending on AC tonnage, electric vs. gas appliances, pool equipment, EV charging, and whether you want true whole-home coverage. A real calculation walks circuit by circuit: it inventories your major loads, applies the largest motor’s surge, adds margin, and arrives at a defensible kW target. That’s what your licensed installer should do.
To get a head start before that visit, our generator sizing calculator lets you rough out a target from your home’s loads, and the sizing overview on the home page covers the basics.
A rough sense of where homes land (not a recommendation)
For orientation only — your numbers will differ:
- Smaller home, one AC system, managed loads: often in the 11–14 kW neighborhood.
- Mid-size home, two AC systems: frequently 18–24 kW, sometimes with load shedding to stay efficient.
- Large home, three-plus AC systems, whole-home coverage: commonly liquid-cooled, 30 kW and up.
These are conversation starters, not spec sheets. The compressor surge, fuel line, and your must-run list move these numbers in both directions.
Where to go next
Once you have a sizing target, think through fuel and installation. Read natural gas vs. propane, then the install-day guide so there are no surprises, and the permitting-by-county guide since Harris, Fort Bend, and Montgomery counties handle approvals differently. When you’re ready for a real load calc, we’ll connect you with our vetted local installer — start from the home page, or your city page: Houston, Sugar Land, or Cypress.