Generator size for a furnace blower
These use typical wattages (running and starting), plus 20% headroom on the running load. Your appliance's label is the best guide.
| What you run | Running | Peak at startup | Generator to shop for |
|---|---|---|---|
| Furnace blower alone | 800 W | 2,350 W | 2,000 running watts |
| + refrigerator, lights, laptop and router | 1,750 W | 3,300 W | 3,000 running watts |
| + the essentials (fridge, sump pump, furnace blower, lights, laptop) | 2,550 W | 4,100 W | 3,500 running watts |
Motors need a surge when they start, which is why the starting watts are higher than the running watts. Build your list in the generator size calculator, and see the generator sizing guide for safety (never run a generator indoors) and how to connect it properly.
Want to change anything else? The calculator above is the full Generator Size Calculator: edit any number and the results update instantly.
Tools & materials for this project
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Frequently asked questions
What size generator do I need to run a furnace blower?
A furnace blower needs about 800 running watts and 2,350 watts at startup, so shop for a generator rated for about 2,000 running watts if it is the only thing you run. Add the watts of anything else you want on at the same time.
Can a 3,500 watt generator run a furnace blower?
Yes. A furnace blower alone needs a generator rated for about 2,000 running watts, and with a fridge, lights, laptop and router about 3,000 running watts.
Can a 2,000 watt generator run a furnace blower?
Yes. With about 2,350 W at startup, check the generator's peak (starting) rating as well as its running rating.
Related sizes and guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.