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What size generator do I need to run my gas furnace in a winter outage?

Q: What size generator do I need to run my gas furnace in a winter outage?

Plan on at least 1300 running watts and 2250 watts of surge capacity. That covers 1035W of running load plus the largest start-up surge, with 25% headroom.

A gas furnace only needs electricity for its blower fan and controls, which makes winter outage coverage surprisingly affordable — the furnace itself keeps making heat as long as the fan can move it.

The load

Furnace blower fan (gas furnace) — 600W running, 1600W starting
Refrigerator (full-size) — 300W running, 1500W starting
LED lights (per room) — 30W running
Wi-Fi router + modem — 15W running
Phone charger — 10W running
TV (55" LED) — 80W running

SIZING PLATE6 LOADS · +25% HEADROOM

Total running watts

1,035 W

Peak (largest start)

2,235 W

Buy at least

1,300 W rated

Look for ~1,300W running / 2,250W surge or better.

Field note: A furnace is hardwired, so you'll need either an interlock kit or transfer switch installed at the panel, or a furnace-specific plug conversion done by an electrician. Plan this before the storm, not during it.

Right size: Mid-size inverter (3,500W / 4,000W surge)

Typical price $600-1,400 · e.g. Champion 4250 open-frame inverter, Westinghouse iGen4500, Generac GP3500iO

RV 13,500 BTU AC (especially with soft-start), fridge + window AC, storm essentials for smaller homes. The sweet spot of quiet, portability, and real capacity for most first-time buyers.

See current prices on Amazon

One size up: Mid-size portable (6,500W / 8,100W surge)

Typical price $700-1,200 · e.g. Westinghouse WGen6500, Champion 6250, Generac GP6500

Storm essentials with margin: fridge, freezer, sump pump, furnace fan, well pump (240V models), lights and electronics together. Louder open-frame design; electronics prefer models with THD under 5% or an inverter.

See current prices on Amazon

Adjust for your setup

Different fridge? Bigger AC? Uncheck and re-check below — the plate recomputes live.

This site earns commissions from qualifying purchases made through links to Amazon and other retailers, at no extra cost to you. Wattage figures are typical estimates — actual draw varies by model. Always verify against your appliance's nameplate, and consult a licensed electrician for any panel or hardwired connections.