Key insight: "Whole-house" generator sizing is almost always overkill for most homeowners. The better question is: what do I actually need to run during an outage? A 2,000–3,500 sq ft home usually needs 5,000–10,000W for essential loads — not the 20,000W a true whole-house generator requires.
Two Ways to Size a Generator
Before diving into numbers, you need to choose your sizing philosophy:
Option A: Essential Load Coverage
You size for only what you actually need during a power outage: refrigerator, freezer, some lighting, a phone charger, possibly a window AC or space heater, and critical systems like a sump pump or well pump. This approach typically requires 5,000–10,000W and costs $800–$5,000 for the generator plus transfer switch.
Option B: Whole-Home Coverage
You size to run everything in the home simultaneously — including central HVAC, electric clothes dryer, electric range, and EV charger. This requires 15,000–25,000W and a permanently installed standby generator costing $8,000–$20,000+ installed. Most homeowners who pay for this rarely use it to full capacity.
Generator Size By Home Square Footage
Square footage is a rough proxy for load — not the correct way to size a generator. Two 2,000 sq ft homes can have very different loads depending on their appliances, HVAC type, and hot water setup. That said, here are realistic ranges:
| Home Size | Essential Load | Whole-Home Load | Recommended Generator |
|---|---|---|---|
| Under 1,500 sq ft | 3,000–5,000W | 8,000–12,000W | 5,000W portable |
| 1,500–2,000 sq ft | 5,000–7,500W | 12,000–16,000W | 7,500W portable or 11kW standby |
| 2,000–3,000 sq ft | 6,000–10,000W | 15,000–20,000W | 9,000W portable or 14–16kW standby |
| Over 3,000 sq ft | 8,000–12,000W | 20,000–30,000W | 11,000W portable or 20–22kW standby |
These are averages. Your actual load depends on your specific appliances. See the load breakdowns below.
Typical Essential Load Breakdown
Here's what a typical essential load looks like for a 2,000 sq ft home with gas heat (furnace blower), a sump pump, and a window AC for one room:
| Appliance | Running Watts | Startup Watts |
|---|---|---|
| Refrigerator | 150W | 600W |
| Chest freezer | 100W | 400W |
| Gas furnace blower | 600W | 2,400W |
| Sump pump (1/2 HP) | 800W | 2,000W |
| Window AC (10,000 BTU) | 1,200W | 3,600W |
| LED lighting (10 bulbs) | 90W | 90W |
| Phone/laptop chargers | 60W | 60W |
| TV + router | 150W | 150W |
| Total (all running) | 3,150W | — |
| Required generator (with surge + 20% buffer) | ~7,000W minimum | |
This example requires a 7,000W generator — well within the range of a standard portable. The surge delta for the window AC (3,600W startup − 1,200W running = 2,400W delta) added to the total running load of 3,150W, plus the 20% buffer, drives the minimum requirement.
What Adds the Most Watts?
These appliances will dramatically increase your generator requirement if included:
- Central air conditioner (2.5–5 ton): 3,500–6,000W running, 7,500–15,000W startup. The single biggest load driver.
- Electric water heater: 4,500W running. Consider delaying water heating or using propane during outages.
- Well pump (1 HP): 1,000W running, 3,000–4,000W startup.
- Electric clothes dryer: 5,000–6,000W. Rarely a genuine emergency need.
- Electric range/oven: 5,000–12,000W. A propane camp stove is a practical substitute during outages.
- EV charger (Level 2): 7,200–9,600W — largest load in modern homes without proper load management.
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