What Will a 4000-Watt Generator Run?
By the Generator Size Calculator Team · Updated · 8 min read
Quick answer: A 4000-watt generator runs the essentials of a small home: a refrigerator, a furnace fan, a microwave, lights, a TV and Wi-Fi at the same time, and it can start a 10,000 BTU central AC. It is too small for a 24,000 BTU central AC with other loads, an electric dryer or a range. This guide assumes 4,000 running and about 5,000 starting watts.
What "4,000 watts" means on your generator
Generators list running watts (what they can supply for hours) and starting watts (a short burst for motors). Some "4000-watt" generators are rated 4,000 running, others 4,000 peak and about 3,500 running. If yours is the second kind, subtract about 12% from the loads below.
This guide assumes about 4,000 running watts and 5,000 starting watts. Check the label on yours. Anything with a motor or compressor needs extra watts for a moment to start, and lights, TVs and heating elements draw about the same all the time. See starting vs running watts.
4,000-watt generator appliance chart
Typical figures from Honda's wattage guide. The last column judges each appliance against 4,000 running watts, an 80% limit of 3,200 watts and about 5,000 starting watts. Your appliance may differ, so check its label.
| Appliance | Running watts | Starting watts | On a 4,000 W generator |
|---|---|---|---|
| Refrigerator or freezer | 700 | 2,200 | Yes, with other loads |
| Sump pump, 1/3 HP | 750 | 1,500 | Yes, with other loads |
| Sump pump, 1/2 HP | 1,000 | 2,100 | Yes, with other loads |
| Sump pump, 1 HP | 2,300 | 4,500 | Yes, start it first |
| Well pump, 1/3 HP | 1,000 | 3,000 | Yes, with other loads |
| Furnace fan, 1/3 HP | 1,000 | 1,800 | Yes, with other loads |
| Microwave (625 W) | 625 | 800 | Yes, with other loads |
| Coffee maker | 1,750 | 1,750 | Yes, start it first |
| Toaster, 2-slice | 1,050 | 1,050 | Yes, with other loads |
| Dishwasher | 1,450 | 1,800 | Yes, with other loads |
| Washing machine | 1,150 | 2,300 | Yes, with other loads |
| Clothes dryer, gas | 700 | 1,800 | Yes, with other loads |
| Clothes dryer, electric | 5,750 | 1,800 | No |
| Electric range, one 8-inch element | 2,100 | 2,100 | Yes, start it first |
| Space heater, high | 1,500 | 1,500 | Yes, with other loads |
| Central AC, 10,000 BTU | 1,500 | 2,200 | Yes, with other loads |
| Central AC, 20,000 BTU | 2,500 | 3,300 | Yes, start it first |
| Central AC, 24,000 BTU | 3,800 | 4,950 | Maybe, on its own, near the limit |
| Central AC, 40,000 BTU | 6,000 | 7,800 | No |
| Air compressor, 1 HP | 1,500 | 4,500 | Yes, with other loads |
| Welder, 100 amp | 3,600 | 3,600 | Maybe, on its own, near the limit |
| TV | 300 | 300 | Yes, with other loads |
| Computer | 150 | 150 | Yes, with other loads |
| Garage door opener, 1/3 HP | 725 | 1,400 | Yes, with other loads |
LED bulbs use about 8 to 15 watts each, and chargers are tiny. For appliances not listed, use the generator wattage calculator.
Example: what a 4,000-watt generator can run at the same time
A realistic outage setup for a small home with a gas furnace:
| Load | Running watts |
|---|---|
| Refrigerator | 700 |
| Furnace fan, 1/3 HP | 1,000 |
| Microwave | 625 |
| TV, lights, chargers, Wi-Fi | 475 |
| Running total | 2,800 |
The running total is 2,800 watts, under the 80% limit of 3,200 watts. Motors rarely start at the same moment, so add only the largest extra start-up load, the refrigerator's 1,500 watts. That gives a peak of about 4,300 watts, under the 5,000-watt starting capacity.
Add your own appliances and see the running and peak watts.
What a 4,000-watt generator can't run
A 4000-watt generator cannot run an electric dryer (5,750 W), an electric water heater (3,000 to 4,500 W per Bob Vila) with other loads, a 24,000 BTU central AC with much else, a 40,000 BTU central AC (6,000 W), or a 2 HP air compressor (7,700 starting watts).
Can a 4,000-watt generator run a house?
It can back up essential circuits in a small home, not everything at once. For a whole house, see whole-house sizing. Many homes with central air need 7,500 watts or more, see what a 7500-watt generator can run.
Tips to get more out of it
- Start the biggest motor first, with nothing else running, then add smaller loads.
- Take turns with heating appliances like the coffee maker, toaster and space heaters.
- Use heavy, outdoor-rated cords. See the extension cord calculator.
- Plan the fuel. See how long a generator runs on a tank of gas.
Safety rules
Run the generator outdoors, at least 20 feet from doors, windows and vents. Never in a garage or shed, even with the door open. See how far a generator should be from your house.
- Install battery-powered carbon monoxide alarms on every level of the home.
- Never plug a generator into a wall outlet. See how to connect a generator to your house.
Frequently asked questions
Can a 4000-watt generator run a refrigerator and a furnace?
Yes. A fridge (700 W) and a 1/3 HP furnace fan (1,000 W) with lights and a TV total about 2,800 watts with the fridge surge on top.
Can a 4000-watt generator run central AC?
A 10,000 BTU central AC (1,500 running, 2,200 starting watts), yes. A 24,000 BTU unit at 3,800 watts leaves almost nothing for other loads.
Can a 4000-watt generator run a well pump?
A 1/3 HP well pump (1,000 running, 3,000 starting watts), yes, with a few other loads. See well pump generator sizes.
Can a 4000-watt generator run a house?
Only the essentials in a small home. Heavy loads like an electric dryer or range need a bigger generator.
4000 watts running or peak?
Check the label. Some models are 4,000 running, others 4,000 peak with about 3,500 running.
Related calculators
Sources: Appliance and tool running and starting watts from the Honda generator wattage guide, space heater watts from Lasko, and typical generator ratings from manufacturer guides. The 80% running-load rule and the assumed starting capacity are our planning assumptions, so confirm the ratings on your own generator.