Heat and water first
In a winter outage on a well, the furnace blower and the well pump are what keep the house livable.[1] Add the fridge and a few lights and you have a realistic winter list.
The well pump is 240 V and the furnace is hardwired, so this setup needs a 240 V generator and a transfer switch or interlock installed by a qualified electrician.[2]
Get ready before the storm
Have the transfer switch or interlock installed before winter. It is what lets a hardwired furnace and well pump run from the generator, and it can’t be improvised during an outage.[2]
Test-run the generator, store fuel safely away from the house, and pick a sheltered spot outdoors, well away from windows, doors and vents.[3]
Put battery carbon monoxide alarms on every level of the house, and never heat it with a gas oven or stovetop if the power fails.[1]
How the number adds up
| Appliance | Running | Starting | Runs |
|---|---|---|---|
| Furnace fan (1/2 HP) | 875 W | 3,150 W | together |
| Well pump (1/2 HP) | 1,000 W | 2,550 W | together |
| Refrigerator | 700 W | 2,900 W | together |
| LED lights (10 bulbs) | 100 W | 100 W | together |
| Running load | 2,675 W | everything together + the biggest “takes turns” item | |
| Worst startup moment | 4,950 W | running load + Furnace fan (1/2 HP) starting (+2,275 W) | |
| Minimum generator | 3,344 W | rated watts (running ÷ 0.8) · how we size | |
Questions
What about a space heater too?
It adds a large steady load. If it can take turns with other heavy items, mark it that way in the calculator.
Can I run the well pump only when we need water?
Yes. With a transfer switch you can turn the well pump’s circuit on, refill the pressure tank and turn it off again. Marking it “can take turns” in the calculator shows how much smaller the generator can be.