What Size Generator Do I Need for a Whole House? Complete 2026 Guide
Updated July 2026 • 12 min read
Quick Answer: What Size Generator for a Whole House?
Most homes need a 20-22kW generator
14kW = essentials only | 22kW = whole home including AC | 26kW = large homes
Choosing the right whole house generator size is the most important decision you'll make when buying backup power. Too small and you'll be left without AC during an outage. Too large and you've wasted money. This guide walks you through exactly how to calculate your needs.
Whole House Generator Size by Home Size (Quick Chart)
| Home Size | AC Size | Recommended Generator | Best Model |
|---|---|---|---|
| Under 1,500 sq ft | 1.5-2.5 ton | 14-16 kW | Generac Guardian 14kW |
| 1,500-2,500 sq ft | 2.5-3.5 ton | 18-20 kW | Generac Guardian 18kW |
| 2,500-3,500 sq ft | 3.5-4 ton | 22 kW ⭐ MOST POPULAR | Generac Guardian 22kW |
| 3,500-5,000 sq ft | 4-5 ton | 24-26 kW | Generac Guardian 26kW |
| Over 5,000 sq ft | 5+ ton or dual zone | 26+ kW or multiple units | Cummins RS30 or dual setup |
Step 1: List Your Must-Have Circuits
During a power outage, what absolutely must stay on? Start with safety and essentials:
Essential Home Circuits — Running vs. Starting Watts
| Appliance | Running Watts | Starting Watts |
|---|---|---|
| Refrigerator | 150-400 | 1,200 |
| Freezer | 100-400 | 1,000 |
| Sump Pump (1/2 HP) | 800 | 2,000 |
| LED Lights (10 bulbs) | 100 | 100 |
| Phone/Device Charging | 50 | 50 |
| WiFi Router | 20 | 20 |
| Garage Door Opener | 550 | 1,100 |
| Essentials Subtotal | ~2,000 | ~5,500 |
Step 2: Add Comfort Appliances (Whole House Coverage)
High-Draw Appliances — The Reason You Need 20kW+
| Appliance | Running Watts | Starting Watts |
|---|---|---|
| Central AC (3 ton) | 3,500 | 7,000 |
| Central AC (5 ton) | 5,000 | 10,000 |
| Electric Water Heater | 4,500 | 4,500 |
| Gas Furnace Blower | 800 | 2,000 |
| Well Pump (1 HP) | 2,000 | 4,000 |
| Electric Range/Oven | 3,000 | 3,000 |
| Microwave | 1,000 | 1,000 |
| TV & Entertainment | 200 | 200 |
Step 3: The Critical Sizing Formula
Whole House Generator Size Formula:
Total Running Watts + Largest Motor's Starting Watts = Minimum Generator Size
Why? Motors (AC, pumps, fridges) need 2-3x more power to START than to run. Your generator must handle that surge.
Real Example: 2,500 sq ft Home with Central AC
Running loads:
- Essential circuits: 2,000W
- Central AC (4 ton): 4,500W running
- Gas furnace blower: 800W
- Additional circuits: 1,500W
Total running load: 8,800W
Largest starting surge: Central AC (4 ton) = 9,000W
Minimum size: 8,800 + 9,000 = 17,800W (18 kW)
Recommendation: 20-22 kW for comfortable headroom ✓
Special Sizing Considerations
Medical Equipment
If anyone in your home relies on powered medical equipment (CPAP, oxygen concentrator, refrigerated medications), size up by at least one tier. Power reliability for medical needs isn't optional — Power Up prioritizes medical households for emergency service.
Home Office
Add 500-1,000W for computers, monitors, and networking equipment. Choose a generator with low Total Harmonic Distortion (THD <5%) to protect sensitive electronics like computers and smart TVs.
Electric Vehicles
Level 2 EV chargers draw 7,200-9,600W. If you need EV charging during outages, add this to your load calculation. Most homeowners use Level 1 charging (1,400W) during outages — much more generator-friendly.
Whole House Generator Sizing FAQ
What size generator do I need for a whole house?
For a whole house, most homeowners need a 20-22kW generator. A 14kW generator powers essential circuits only (refrigerator, lights, sump pump, some outlets). A 22kW generator powers your whole home including central AC up to 4 tons. For homes over 3,000 sq ft with 5-ton AC, a 24-26kW is recommended. The most popular whole house generator is the Generac Guardian 22kW.
Can a 14kW generator run a whole house?
A 14kW generator can run essential circuits of most homes but typically cannot power central air conditioning simultaneously. It's adequate for lighting, refrigerator, sump pump, furnace blower, small appliances, and outlets. If whole house coverage including AC is your goal, a 20-22kW generator is the minimum recommended size.
Can a 22kW generator run a whole house?
Yes, a 22kW generator can run most entire homes. The Generac Guardian 22kW is the most popular whole house generator and handles homes up to 3,500 sq ft with central AC up to 4 tons. It powers all essential circuits plus AC, water heater, and most appliances simultaneously. For homes over 3,500 sq ft or with 5-ton AC, consider a 24-26kW unit.
How many watts does a whole house use?
An average American home uses 1,200-2,000 running watts for basic circuits. When you add central air conditioning (3,500-5,000 running watts) and other appliances, total running wattage reaches 6,000-12,000 watts. Most importantly, motor starting surge can double these numbers briefly. A 20-22kW (20,000-22,000 watt) generator provides comfortable headroom for the average home.
What size generator do I need for a 2,000 sq ft house?
A 2,000 sq ft house typically needs a 16-20kW generator for whole house coverage. This size handles all essential circuits plus central AC up to 3.5 tons. If you have a large AC system, electric water heater, or multiple high-draw appliances, size up to 20-22kW. Get a free load calculation from our experts to confirm the right size for your specific home.
What size generator do I need for a 3,000 sq ft house?
A 3,000 sq ft house typically needs a 22-24kW generator for complete whole house backup power. Larger homes have more circuits, bigger AC systems (typically 4-5 tons), and higher overall electrical demand. A 22kW Generac Guardian is often sufficient if the AC is 4 tons or less. For 5-ton systems or two-zone AC, consider 24-26kW.
Get Your Free Whole House Generator Sizing Assessment
Our factory-trained experts will calculate exactly what size you need — no guesswork, no overselling. As a nonprofit, we never upsize you beyond what you need.