Furnace Blower Fan Wattage for Generator Sizing
About the Furnace Blower Fan
The blower fan motor in a gas or oil furnace that circulates heated air through ductwork. Even though the furnace itself burns fuel, the blower requires electricity to distribute heat throughout the home. The starting surge is typical of any motor-driven load. For homes with gas or oil heat, powering the furnace blower with a generator provides whole-house heating at a fraction of the electrical cost of running electric heat. The furnace control board and igniter also require power, but their draw is minimal compared to the blower motor.
Generator Sizing for a Furnace Blower Fan
Running a furnace blower fan by itself requires a generator with at least 1,625 W of capacity (2 kW), which includes a 25% safety margin. However, you rarely run a single appliance on a generator. When combined with other appliances, the furnace blower fan contributes 800 W to the continuous running load and adds a potential 500 W starting surge gap when its motor starts.
The furnace blower fan is an inductive (motor-driven) load with a starting surge of 1,300 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 furnace blower fan has the largest starting surge gap of any appliance in your generator load, its surge gap of 500 W will be the primary driver of your peak demand calculation. Avoid starting the furnace blower 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 furnace blower 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 furnace blower fan.
Scenarios That Include Furnace Blower Fan
The following pre-calculated generator scenarios include the furnace blower fan in their appliance list. Each scenario shows the total generator size needed for all appliances in the set, not just the furnace blower fan alone. Click any scenario to see the full appliance breakdown.
| Scenario | Total Appliances | Running Watts | Recommended Size |
|---|---|---|---|
| Power Outage Essentials | 5 | 1,095 W | 2 kW |
| Whole House Basic Coverage | 8 | 3,895 W | 7 kW |
| Winter Storm Preparedness | 7 | 3,595 W | 6 kW |
| Well Water Home Essentials | 7 | 4,095 W | 8 kW |
| Full Disaster Preparedness Kit | 11 | 4,105 W | 7 kW |
Tips for Running a Furnace Blower Fan on a Generator
When running the furnace blower fan on a generator, the most important consideration is the starting surge. Before starting the furnace blower fan, check that no other large motor-driven appliances are starting simultaneously. Stagger your startups: let the furnace blower fan reach steady-state operation (usually within 1-2 seconds) before starting the next motor load.
If the generator struggles to start the furnace blower 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 furnace blower 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 furnace blower fan, verify that the generator's peak (starting) wattage specification meets or exceeds the 1,300 W starting requirement plus the running wattage of all other connected appliances.
Furnace Blower Fan Wattage Compared to Similar Appliances
The following table compares the furnace blower 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 |
|---|---|---|
| Furnace Blower Fan (this appliance) | 800 W | 1,300 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 | — |
| Whole House Fan | 500 W | 800 W |
| Dehumidifier | 650 W | 800 W |
Frequently Asked Questions
How many watts does a furnace blower fan use?
A furnace blower fan uses approximately 800 watts of continuous (running) power during normal operation. It also requires 1300 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 furnace blower fan?
To run a furnace blower fan by itself, you need a generator rated for at least 1,625 W (2 kW), which includes a 25% safety margin above the starting wattage of 1300W. However, most people run additional appliances alongside the furnace blower 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 furnace blower fan on an inverter generator?
Yes, a furnace blower fan can run on an inverter generator as long as the generator's peak (starting) wattage capacity meets or exceeds 1300 watts. Inverter generators handle motor starting surges well and provide clean power that is safe for the electronic controls found in many modern furnace blower fan models. Verify the inverter generator's surge rating in the specifications.