What Size Generator Do I Need? Whole House Generator Sizing Guide 2026
The average American home needs a 16-22 kW whole-house generator to power essential and most standard loads during an outage. A 22 kW unit can handle a 2,000-2,500 sq ft home with central AC, refrigerator, lights, and most appliances. Smaller homes or essentials-only coverage may only need 10-16 kW. Installation cost: $12,000-$18,000 including the generator, automatic transfer switch, fuel connection, and concrete pad.
How to Size a Generator
Generator sizing requires adding up the running watts of all appliances you want to power, then accounting for starting watts (surge) of motor-driven loads. Key loads: Central AC (3,500-5,000W running, 7,000-10,000W starting), Refrigerator (150W running, 400W starting), Well Pump (1,000W running, 2,500W starting), Sump Pump (800W running, 2,000W starting), Lights and outlets (2,000-3,000W). Total running: approximately 8,000-12,000W for a typical home. Add largest starting surge: +5,000W for AC. Peak demand: 13,000-17,000W = 16-22 kW generator.
Generator Size by Home Size
1,000 sq ft (essentials only): 10 kW — fridge, lights, outlets, sump pump. No AC. 1,500 sq ft (most loads): 16 kW — adds window AC or small central AC. 2,000 sq ft (full coverage): 22 kW — central AC, all lights, kitchen, laundry. The most popular residential size. 3,000 sq ft (large home): 30 kW — handles everything including larger AC and EV charger. 4,000+ sq ft: 48 kW — multiple AC zones, pool equipment, full large home. Use our Electrical Load Calculator for exact sizing.
Fuel Types: Natural Gas vs Propane vs Diesel
Natural gas: Most popular for residential — connects to existing gas line, unlimited fuel supply, lowest per-kWh cost (~$0.12/kWh). Propane (LP): Good for homes without gas lines. Requires a tank (500-1,000 gallon recommended). Slightly higher cost (~$0.15/kWh) but reliable. Diesel: Most efficient and longest-lasting, but noisier, requires fuel storage, and not common for residential. Dual-fuel (NG/LP): Available from most manufacturers — provides flexibility and backup redundancy. Generac, Kohler, and Briggs & Stratton all offer dual-fuel residential units.
Transfer Switch Requirements
NEC Articles 700, 701, and 702 require an automatic transfer switch (ATS) for all permanently installed generators. The ATS detects a power outage, waits 10-30 seconds to confirm, then starts the generator and transfers the home electrical load. When utility power returns, the ATS transfers back and shuts down the generator. All modern whole-house generators include or require an ATS — typical cost is $500-1,000 included in the installation price. The ATS is installed next to or integrated into your main electrical panel.
| Home Size | Generator | Covers | Installed Cost |
|---|---|---|---|
| 1,000 sq ft | 10 kW | Essentials only | $8,000-$12,000 |
| 1,500 sq ft | 16 kW | Most loads, small AC | $10,000-$14,000 |
| 2,000 sq ft | 22 kW | Everything + AC | $12,000-$18,000 |
| 3,000 sq ft | 30 kW | Large home, dual AC | $15,000-$22,000 |
| 4,000+ sq ft | 48 kW | Full large home | $20,000-$30,000 |
Installation Cost Breakdown
Generator unit: $4,000-$8,000 (16-22 kW). Automatic transfer switch: $500-$1,000 (often included). Concrete pad: $200-$500. Gas line connection: $500-$1,500. Electrical installation: $1,500-$3,000. Permits and inspection: $200-$500. Total: $12,000-$18,000 for a quality 22 kW installation. Financing is available from most dealers — typical terms are $200-$300/month for 5-7 years. Check for manufacturer promotions and utility rebates. Installation typically takes 1-2 days after the concrete pad cures.
Disclaimer: For educational reference only. Consult a licensed professional.