Sizing for a Furnace Blower or Boiler — Keeping the Heat On
Last verified: September 2026
How to keep the heat on in a winter outage: even gas heat needs electricity for its blower or circulator pump, and this guide shows you what to size for and why an electrician joins the plan. Rather talk it through? My number is (330) 200-8042.
Sizing for Heat, at a Glance
When the power fails on a cold night, heat comes first — and here's the surprise: even gas heat needs electricity. A gas or oil furnace runs on its blower fan motor (which surges) plus ignition and controls; a boiler runs on its circulator pump(s). Those are modest, motor-sized loads. But all-electric heat and heat pumps make the warmth with electricity — a much bigger ask, often beyond a portable. And because heat is hardwired, it needs a transfer switch and a licensed electrician. This guide covers all three, with a printable version up top.
Common Questions
1 Why does my gas furnace need electricity?
The gas makes the heat, but electricity runs the blower fan that moves warm air through the house, plus the ignition and controls. Cut the power and a gas furnace sits silent — so heat belongs on your backup list even with gas.
2 What do I actually size for with a furnace?
Mainly the blower motor. Like any motor it needs a brief starting surge several times its running watts, so size for that jolt plus the steady draw. The small ignition and controls ride along easily.
3 I have a boiler — what's different?
A boiler heats water and uses circulator pumps to move it to the radiators. Those pumps are the electric load — smaller motors than a forced-air blower, but count every circulator that might run at once.
4 Will a portable generator run all-electric heat?
Often not. An all-electric furnace or a heat pump's backup heat makes warmth with electricity, running into the thousands of watts — usually more than a portable can give. That points to a standby unit and a professional load calculation.
5 Can I just plug my furnace into a generator?
Almost never — furnaces and boilers are hardwired, with no plug. They need a transfer switch or interlock installed by a licensed electrician. I help you size and plan, then coordinate that electrician for you.
6 My well pump and furnace both need to run — how?
Size around the bigger surge (usually the well pump), then stagger the starts so the pump and blower don't jolt to life together. Run the pump to build water, then let the blower carry heat. See our guide on managing loads during a run.
Would You Rather I Just Help?
Heat is too important to size on a guess. I'll help you identify your system, find the motor that matters, read its nameplate, and coordinate the licensed electrician for the hookup — so you're warm when the power's out, with nothing to sell you. $99 flat for a visit, 30-day come-back-free.
Would you rather I just do this for you?
No shame in it — plenty of folks would rather hand it off, and that's what I'm here for. I'll come to your home, set it up right, and make sure it's working before I leave. Flat $99 per visit — no jargon, no upsell, and every visit is 30-day come-back-free.
Not a hardware job? I can often fix it remotely for $49 — a secure screen-share, up to 2 hours, that you watch the whole time and can end whenever (included free for $39/mo Support Plan members, and it counts toward the $99 if it turns out I need to come out).