Whole House Fan Wattage for Generator Sizing
About the Whole House Fan
A whole house fan mounted in the ceiling that pulls air through the house and exhausts it through attic vents. These fans are an energy-efficient alternative to air conditioning in mild climates and can cool a house rapidly during cooler evening hours. The motor startup surge is moderate. Whole house fans are a good option for generator-powered cooling because they draw significantly less power than air conditioning systems while still providing meaningful temperature reduction.
Generator Sizing for a Whole House Fan
Running a whole house fan by itself requires a generator with at least 1,000 W of capacity (1 kW), which includes a 25% safety margin. However, you rarely run a single appliance on a generator. When combined with other appliances, the whole house fan contributes 500 W to the continuous running load and adds a potential 300 W starting surge gap when its motor starts.
The whole house fan is an inductive (motor-driven) load with a starting surge of 800 W, which is 1.6 times its running wattage. This starting surge occurs for a fraction of a second when the motor first engages and must overcome inertia to begin rotating. Your generator must be capable of delivering this peak wattage even though it only lasts briefly. If the whole house fan has the largest starting surge gap of any appliance in your generator load, its surge gap of 300 W will be the primary driver of your peak demand calculation. Avoid starting the whole house fan at the same time as other large motor loads to prevent generator overload.
To determine the total generator size you need, use our interactive calculator to combine the whole house fan with your other appliances. The calculator automatically handles the starting surge calculation and applies the 25% safety margin to give you an accurate recommendation. Alternatively, browse the scenarios below to see common generator setups that include the whole house fan.
Tips for Running a Whole House Fan on a Generator
When running the whole house fan on a generator, the most important consideration is the starting surge. Before starting the whole house fan, check that no other large motor-driven appliances are starting simultaneously. Stagger your startups: let the whole house fan reach steady-state operation (usually within 1-2 seconds) before starting the next motor load.
If the generator struggles to start the whole house fan (indicated by the generator bogging down, lights dimming significantly, or the appliance failing to start), it likely means the generator's peak surge capacity is insufficient. Try reducing other loads before attempting to start the whole house fan again. If the problem persists, you may need a larger generator with more surge capacity.
Modern inverter generators handle motor starting surges particularly well due to their electronic power management. If you are purchasing a new generator specifically for loads that include the whole house fan, verify that the generator's peak (starting) wattage specification meets or exceeds the 800 W starting requirement plus the running wattage of all other connected appliances.
Whole House Fan Wattage Compared to Similar Appliances
The following table compares the whole house fan to other appliances in the hvac & climate category. Understanding relative power requirements helps you make informed decisions about which appliances to prioritize on your generator and where you might find opportunities to reduce your total load.
| Appliance | Running Watts | Starting Watts |
|---|---|---|
| Whole House Fan (this appliance) | 500 W | 800 W |
| Central Air Conditioner (3-Ton) | 3,500 W | 4,500 W |
| Window AC Unit (5,000 BTU) | 500 W | 600 W |
| Window AC Unit (10,000 BTU) | 1,200 W | 1,500 W |
| Portable Space Heater | 1,500 W | — |
| Furnace Blower Fan | 800 W | 1,300 W |
| Dehumidifier | 650 W | 800 W |
Frequently Asked Questions
How many watts does a whole house fan use?
A whole house fan uses approximately 500 watts of continuous (running) power during normal operation. It also requires 800 watts of starting (surge) power when the motor first turns on, which is 1.6 times the running wattage. This starting surge lasts only a fraction of a second but your generator must be capable of delivering it.
What size generator do I need to run a whole house fan?
To run a whole house fan by itself, you need a generator rated for at least 1,000 W (1 kW), which includes a 25% safety margin above the starting wattage of 800W. However, most people run additional appliances alongside the whole house fan, so your actual generator needs will be higher. Use our calculator to add your other appliances and get a comprehensive recommendation.
Can I run a whole house fan on an inverter generator?
Yes, a whole house fan can run on an inverter generator as long as the generator's peak (starting) wattage capacity meets or exceeds 800 watts. Inverter generators handle motor starting surges well and provide clean power that is safe for the electronic controls found in many modern whole house fan models. Verify the inverter generator's surge rating in the specifications.