Can a Solar Generator Run a Gas Furnace?

The number you need

Almost all of the draw is the blower motor. Which kind you have decides everything:

Typical figures for US residential gas furnaces. The data plate inside your furnace door gives the real amperage — multiply amps by 120.

If your furnace was installed after roughly 2010, or if the fan ramps up gradually instead of slamming on, you probably have an ECM. That is the good outcome: a 300-watt load with no meaningful surge, which nearly any 1,000Wh unit handles.

If it bangs on at full speed, assume PSC and assume a 2,000-watt surge. Now you need a unit with at least a 1,800W inverter, and preferably more.

How long a battery actually lasts

Your furnace does not run continuously. In a well-insulated house at 20°F outside, the blower might run fifteen minutes an hour. A badly insulated one, closer to thirty.

At 500 watts running, fifteen minutes an hour:

• 500Wh unit → about 4 hours
• 1,000Wh unit → about 8 hours
• 2,000Wh unit → about 16 hours
• 4,000Wh unit → a day and a half

Turn the thermostat down to 60°F and those numbers stretch by roughly a third. You are not trying to be comfortable, you are trying to keep the pipes from freezing and the family from getting cold. Sixty degrees is a survivable house.

The catch nobody mentions: it is hardwired

Here is where most people hit a wall. Your furnace is not plugged into an outlet. It is wired directly into a circuit in your panel, usually a dedicated 15A breaker.

You cannot run an extension cord to it. There are exactly three legitimate ways round this:

A transfer switch or interlock kit. A licensed electrician installs it, you plug the power station into an inlet, and the furnace circuit runs off the battery. This is the correct answer and costs roughly $400–$900 installed, depending on which you choose. See Interlock Kit vs Transfer Switch.

A furnace outlet conversion. An electrician replaces the hardwired connection with a plug and receptacle on the furnace itself. Cheaper than a transfer switch, and then you unplug the furnace and plug it into the battery when the power goes. Some jurisdictions allow this, some do not.

Nothing. If neither of those is happening this winter, your battery is for the fridge, the phones and an electric blanket instead. That is still a good outcome — see Can a Power Station Run an Electric Blanket?.

What you must not do is backfeed the circuit through a dryer outlet or any other double-male cord. That kills lineworkers. Here is why it is illegal everywhere in the US.

Boilers and heat pumps are different

Hot water boilers are even better news. The circulator pump draws 70–150 watts and there is no big blower. A 1,000Wh unit can run one for the best part of a day.

Heat pumps are a no. The compressor is the whole appliance, and it draws thousands of watts continuously. That is not a power-station job, it is a generator job. If you heat with a heat pump and no gas backup, plan around a wood stove, a propane heater rated for indoor use, or leaving.

Electric furnaces are also a no, and it is not close. Resistance heat strips pull 10,000 to 20,000 watts.

What we would tell a neighbour to buy

If you have a gas furnace and an ECM blower, a 1,000Wh unit with a 1,500W+ inverter covers a normal overnight outage and does the fridge too. That is the sweet spot and it is around $600–$800.

If you have a PSC blower, size up to something with a 1,800W inverter minimum, because the surge is what kills you, not the capacity.

Do not buy a 500Wh unit for this job. It may not start a PSC blower at all, and even with an ECM it gives you four hours. Four hours is not an ice storm.

Test it before winter

Once the transfer switch is in, run a drill on a mild day. Kill the breaker, plug the furnace into the battery, and drop the thermostat until the furnace calls for heat. Watch the power station's load readout at the moment the blower starts — that spike is the number that matters, and now you have measured it instead of guessing.

Then write the wattage on a piece of tape and stick it on the furnace. In February at 2am you will not want to be doing arithmetic.

The short version

• Gas furnace on a battery is the best value in backup heat: a few hundred watts warms the whole house.
• ECM blowers draw 100–300W with no surge. PSC blowers draw 400–800W and surge to 2,000W.
• A 1,000Wh unit runs a typical furnace roughly 8 hours at 15 minutes per hour.
• The furnace is hardwired, so you need a transfer switch, an interlock, or a furnace receptacle installed by an electrician.
• Heat pumps and electric furnaces cannot be run on any portable battery.