The short answer: yes, if you have a gas or oil furnace. The heat comes from burning fuel, and only the blower, ignition and controls are electric, which is 400 to 600W while the blower is running. Our pick is the Jackery HomePower 3600 Plus, because it expands to 21kWh and is transfer-switch ready.
The answer is no for an electric furnace or a heat pump. Those make heat from electricity instead of fuel, need 240V, and take a 7,200W unit such as the Solar Generator 5000 Plus. Here is the arithmetic and the wiring.
Why a gas furnace is an easy load
A gas furnace looks like a huge appliance and behaves like a small one during an outage. The burner makes the heat from gas. Electricity only does three jobs: it spins the blower that pushes warm air through the ducts, it lights and controls the burner, and it powers the thermostat.
That comes to 400 to 600W while the blower is running, which is less than a hairdryer. Any of the three Jackery home units delivers 3,600W or more, so starting and running it is never the question. Capacity is.
The blower cycles with the thermostat rather than running continuously. In mild weather it runs a few minutes an hour. In deep cold it runs most of the time, and that is when a gas furnace uses 3,000 to 5,000Wh a day. An oil furnace is the same story, and so is a boiler with circulator pumps, which sit in the same 400 to 600W range.
Runtime for the three units
Every figure below is on the battery alone, no solar, with the furnace counted at 4,000Wh a day, the middle of the deep-cold range. Essentials means a fridge, Wi-Fi, a few lights and phones, which together come to about 2,100Wh a day.
| Load | Energy per day | HomePower 3000 (3,072Wh) | HomePower 3600 Plus (3,584Wh) | 5000 Plus (5,040Wh) |
|---|---|---|---|---|
| Furnace alone, deep cold | ~4,000Wh | 15 hours to a day | About a day | About 1.25 days |
| Furnace plus essentials | ~6,100Wh | About 12 hours | About 14 hours | About 20 hours |
| Furnace plus essentials, expanded | ~6,100Wh | Not expandable | 3.5 days at 21kWh | About 10 days at 60kWh |
| Milder cold, furnace at 3,000Wh | ~5,100Wh | About 14 hours | About 17 hours | About a day |
Read the third row twice, because it is the whole point of this page. On its own battery the HomePower 3600 Plus buys you a night and a morning. With expansion packs it buys you the rest of the storm. A winter outage that lasts three days is common in the northern plains and the upper Midwest, and our North Dakota outage guide and Wisconsin outage guide size for exactly that.
Solar is a smaller help in winter than people hope. A grey winter day returns a few hundred watt-hours against a 6,000Wh day. A bright, cold, clear day returns more, but never plan a January outage on the panels. Charge to full before the storm arrives and treat any sun as a bonus.
▶ Shop the HomePower 3600 Plus, expandable to 21kWh
The two ways to connect it
A furnace is usually hardwired or plugged into a receptacle inside the cabinet, so you cannot simply run an extension cord to it. There are two legitimate answers, and both involve a licensed electrician.
A plug and receptacle at the furnace. An electrician fits a cord and plug to the furnace and a receptacle beside it. In normal times the furnace is plugged into the wall receptacle. During an outage you unplug it and plug it into the battery. This is the cheaper option, it takes an hour of an electrician’s time, and it works with any unit.
A transfer switch. An electrician wires a transfer switch into your panel and picks the circuits it feeds: the furnace, the fridge, a few lights, maybe the sump pump. During an outage you flip the switch and those circuits run from the battery with no cords anywhere. It costs more and it is far better to live with at 3 a.m. in a snowstorm. The HomePower 3600 Plus is transfer-switch ready, which is a large part of why it is the pick here.
Never backfeed a wall outlet. Running a cord from a generator into a receptacle to energise the house is not a shortcut, it is a way to kill someone. It puts power back onto the utility lines where a lineworker is working, it bypasses every breaker in the house, and it has burned houses down. A transfer switch exists precisely so nobody has to try it.
Why a space heater is the wrong plan
The instinct during a winter outage is to skip the furnace and plug in an electric space heater. The arithmetic kills it.
A space heater draws 1,500W continuously. That drains a 3,000Wh battery in about two hours, and it heats one room. A gas furnace blower draws 400 to 600W and cycles, so the same battery keeps the whole house above freezing for most of a day. The furnace wins by three or four times, because the gas is doing the heating and the battery is only moving air.
Keep a space heater for the case where the furnace itself has failed, and expect to run it for an hour at a time rather than all night.
Boilers and circulator pumps
If you heat with hot water rather than forced air, the electric load is the circulator pump or pumps that push water through the loops, plus the burner controls. Those sit in the same 400 to 600W range as a blower, so the runtimes above apply.
The practical difference is that a hydronic system holds heat in the water and the radiators, so it coasts longer between cycles than a forced-air system does. Count your zones: a house with three circulator pumps running at once is at the top of that range rather than the bottom.
The thermostat, including the smart one
A conventional thermostat is powered by the furnace’s own low-voltage transformer, so it comes back on when the furnace does. There is nothing extra to do.
A Wi-Fi thermostat needs two things: the furnace powered, and your router powered. A router is about 10W, roughly 240Wh a day, which is trivial next to the furnace, so put it on the battery and leave it there. If the thermostat loses its connection it usually falls back to controlling the furnace directly, but some models want a moment to reconnect. Check yours once during a test rather than finding out in a storm.
Set the thermostat lower than usual during an outage. Every degree you do not ask for is blower time you do not spend. Sixty degrees keeps pipes safe and the house liveable, and it can add hours to the runtime figures above.
Test it once in autumn
Do this in October, on a mild day, with the grid up and daylight outside.
- Charge the unit to full.
- Plug the furnace into it, or throw the transfer switch, whichever setup you had fitted.
- Turn the thermostat up until the burner lights and the blower runs.
- Watch the unit’s display and write down the actual running watts of your own furnace. It will be within the 400 to 600W range, and knowing your number beats using ours.
- Let it run for an hour, note how many watt-hours it used, and multiply by the hours a day your blower runs when it is genuinely cold.
- Turn everything back, and charge the unit to full again.
That one hour tells you whether your unit carries your furnace overnight or all weekend, and it is the difference between a plan and a hope.
Who needs the 5000 Plus
Step up from the HomePower 3600 Plus in three cases.
- You have an electric furnace or a heat pump. Those need 240V and the output only a 7,200W unit provides. No 120V battery will run them, whatever its capacity.
- You are on a well. A well pump draws about 1,000W running and two to three times that to start, on 240V. A house with heat and no water is not a house you can stay in.
- You want central AC in summer from the same unit. Central AC is 3,000 to 4,000W with a large surge, on 240V.
If none of those apply and you burn gas or oil, the HomePower 3600 Plus with at least one expansion pack is the right answer. Our HomePower 3600 Plus review works through a three-day winter outage with it, and the home backup buying guide sets it against the alternatives.
▶ See current Jackery deals before winter
Keep reading: Best solar generators for home backup · Jackery HomePower 3600 Plus review · Solar generator vs gas generator · Keeping power during a North Dakota outage · Keeping power during a Wisconsin outage