What Size Generator Do I Need for My House?
The right standby generator size depends on your home's square footage and which appliances must keep running. Here's how to estimate — and why your installer's load calculation has the final word.
Generator size is measured in kilowatts (kW) — the amount of electrical power the unit can produce continuously. Too small and the generator overloads and shuts down right when you need it; too big and you've overspent by thousands. Here's a practical starting point for Texas homes:
Recommended Size by Home Square Footage
| Home size | Typical recommendation | What it usually covers |
|---|---|---|
| Under 1,500 sq ft | 10–14 kW | Essentials or modest whole-home: fridge, lights, internet, small AC |
| 1,500 – 2,500 sq ft | 18–22 kW | Whole home for most families, including central AC |
| 2,500 – 3,500 sq ft | 22–26 kW | Larger homes; often two AC zones with load management |
| Over 3,500 sq ft | 26–48 kW | Large or all-electric homes; liquid-cooled units common |
These are rules of thumb for planning and budgeting. Your installer's load calculation — based on your actual panel, appliances, and priorities — determines the final size.
Common Household Loads (Running Watts)
Installers size generators from the appliances you need during an outage. Some typical running wattages:
| Appliance | Running watts | Starting surge |
|---|---|---|
| Central AC, 3-ton | ~3,500 | ~7,000 (brief surge) |
| Central AC, 5-ton | ~5,000 | ~10,000 (brief surge) |
| Refrigerator / freezer | ~700 each | ~2,200 |
| Electric water heater | ~4,500 | — |
| Electric clothes dryer | ~5,000 | — |
| Electric range / oven | ~8,000–12,000 | — |
| Well pump, 1 HP | ~1,000 | ~3,000 |
| Lights (whole home, LED) | ~300–600 | — |
| Internet / TV / computers | ~400–800 | — |
| Medical devices (CPAP, oxygen) | ~100–600 | — |
Wattages are typical values; check your appliances' nameplates for exact numbers. Motor-driven appliances (AC, fridge, well pump) draw a much larger surge for a few seconds at startup — that's what the generator must handle.
The AC Question (It Matters Most in Texas)
In the Coastal Bend, air conditioning is usually the single biggest load — and the one homeowners care about most. A 3-ton central AC needs about 3,500 running watts but can surge to 7,000+ at startup. That surge is why a home whose steady load is only 12 kW might still need a 20–22 kW generator.
Load-management modules are the smart workaround: inexpensive devices that stage large loads so they never start at the same instant. They can let a smaller generator handle a bigger home — ask your installer about them.
Whole-Home vs. Essentials-Only
- Whole-home: the transfer switch backs up your entire panel. Maximum convenience, larger (pricier) unit.
- Essentials-only (managed): selected critical circuits go on the generator; the rest stay dark during outages. Smaller unit, $2,000–$4,000 less, and honestly all many families need.
There's no wrong answer — it's a budget and lifestyle choice. Be deliberate about the list: fridge, a way to cool one or two rooms, lights, internet, medical devices, and maybe the garage door opener.
Frequently Asked Questions
What size generator do I need for a 2,000 sq ft house?
Most 2,000 sq ft homes in Texas are well served by a 20–22 kW standby generator, which typically covers the whole home including central AC. Your installer will confirm with a load calculation based on your actual appliances.
Is it bad to oversize a generator?
Mildly oversizing is fine and common — it gives headroom for starting surges from AC compressors. Grossly oversizing wastes money upfront and can cause a lightly-loaded engine to run inefficiently. This is why a proper load calculation beats guessing.
Can I just back up essential circuits instead of the whole house?
Absolutely — and it's a legitimate way to save $2,000–$4,000. An essentials-only setup (fridge, lights, internet, one small AC or fans, medical devices) can run on a 10–14 kW unit. Just be deliberate about which circuits make the cut.
Do I need a bigger generator for two AC units?
Usually, yes — or at least load-management modules that stage the ACs so they don't start simultaneously. Two 3-ton units starting at once create a huge surge; your installer will design around it.
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