Can a generator run your furnace or heat pump during a power outage?

Every few winters an ice storm takes the power out across Clark County for days. In the February 2021 storm about 24,000 Clark PUD customers lost power, and across the river PGE had 421,649 customers out, the largest outage in Oregon history. In January 2024 it happened again: 24,675 Clark PUD customers were out over one weekend, and PGE counted 524,600 outages over nine days.

When the power goes, so does your heat. Even a gas furnace needs electricity for its blower, igniter and controls. So the question we hear after every storm is simple: can a generator keep the heat on? Here are the real numbers, the right kind of generator for each system, and the two mistakes that hurt people in every outage.

How much power your heating system needs.

Heating systems draw very different amounts of power. These figures come from the manufacturers' own spec sheets:

Two things stand out. A gas furnace is a small electrical load, which is one of the real reasons dual-fuel systems appeal to people who worry about outages. And a heat pump draws the most when it is coldest, exactly when you need it.

Inverter heat pumps start gently.

The hardest moment for a generator is the instant a compressor starts. An old single-speed compressor pulls a big surge of current for a split second. A modern inverter compressor ramps up slowly instead.

You can see it on the spec sheets. A single-stage 3-ton American Standard heat pump lists a locked-rotor (starting) current of 72.2 amps against 14.7 amps running. The variable-speed 3-ton version lists 10.2 amps starting against 18.4 amps running, so its start is gentler than its normal run. Mitsubishi says the same about its inverter systems: they soft-start, so the generator does not need to be oversized for a big startup surge. In one Mitsubishi case study, a 3.5-ton ducted Hyper-Heat system plus six other household circuits ran for an 18-hour outage on an 8,000-watt-class Generac portable connected through a transfer switch.

If you have an older single-speed heat pump or AC, a soft starter such as the Micro-Air EasyStart can cut that starting surge by up to 75%, which can be the difference between a generator that runs it and one that stalls.

Emergency heat is the wattage trap.

Most heat pump thermostats have an Em Heat (emergency heat) setting. It shuts the compressor off and runs only the backup heat, which in most air handlers means electric heat strips. That turns a load of about 2,900 watts into 10,000 to 20,000 watts. On a generator, keep the thermostat out of emergency heat unless the generator was sized for the strips. Many systems also bring the strips on automatically as auxiliary heat when the heat pump falls behind, so ask your installer whether yours can lock them out while you run on a generator. A large portable cannot run them at all, and even a 22 kW standby generator would spend nearly all its output on a 20 kW strip set.

Clean power: why an inverter generator.

Modern furnaces and heat pumps run on electronics: variable-speed blower motors, inverter compressor drives and communicating controls. They care about power quality, not just watts.

• Generac rates its inverter generators at 3% total harmonic distortion (THD) or less, standard portables typically at 9 to 15% (some up to 30%), and its standby units under 5%, which it calls suitable for variable-speed HVAC.
• Lennox's install manual for one of its variable-speed furnaces asks for generator power under 5% THD, 102 to 132 volts and 57 to 63 hertz, with correct polarity and ground. Trane notes its furnace controls are polarity sensitive.
• Mitsubishi asks for clean voltage between 187 and 253 volts on its 240-volt heat pumps.

The practical rule: run modern heating equipment on an inverter generator or a standby generator, not a cheap open-frame portable.

Portable or standby?

Both work. They suit different homes.

• Small inverter portable (about 2,000 watts). A Honda EU2200i is rated at 1,800 watts running. That covers a gas furnace with room to spare, or one small ductless head at moderate output. It will not run a ducted heat pump.
• Large portable (about 6,000 to 8,000 watts). Clark Public Utilities notes portable generators provide up to about 6,000 watts. With a transfer switch, that runs a furnace plus essentials, and as Mitsubishi's case study shows, a larger low-distortion portable can carry a 3.5-ton inverter heat pump. Gasoline has to be stored outside living areas and refilled through a long outage.
• Standby (about 10 to 26 kW). Generac's air-cooled standby units run from 10 kW to 26 kW on propane or natural gas and start on their own when the power fails. They run on your gas supply for as long as it lasts. During the January 2024 storm, NW Natural kept gas flowing to about 2 million people, many of whom had no electricity. A properly sized standby unit can run a heat pump and the rest of the house; only the largest can also carry heat strips.

Connecting it safely.

This is where people get hurt. Never backfeed a generator by plugging it into a wall outlet or a dryer outlet with a "suicide cord" (a cord with a plug on both ends). The CPSC warns it can electrocute utility line workers and neighbors on the same transformer, and it bypasses your home's circuit protection. Generac calls the dryer-outlet hookup improper, and in March 2026 the CPSC warned consumers to stop using male-to-male cords entirely.

The right way is a transfer switch or a breaker interlock. Both make it physically impossible for the generator and the utility to feed your house at the same time. Generators connected to house wiring fall under the electrical code's rules for optional standby systems (NEC Article 702).

In Clark County, a permanently connected generator needs an electrical permit, a licensed electrician and a "break before make" transfer switch, according to Clark Public Utilities. Washington L&I's permit fee as of July 1, 2026 is $109.90 for a portable generator with permanent transfer equipment and $129.40 for a permanent generator. The City of Vancouver issues its own electrical permits; Camas, Battle Ground, Ridgefield and Washougal go through L&I.

Carbon monoxide: the deadliest mistake.

A generator makes carbon monoxide you cannot see or smell. During the February 2021 ice storm, four people died of carbon monoxide poisoning in Clackamas County, and a Gladstone family of six went to the hospital after running a generator in their basement.

• Never run a generator inside the house, garage, basement, crawlspace or shed, even with the doors and windows open.
• Keep it outside, more than 20 feet from the house, doors, windows and vents, per the CDC and CPSC.
• Put battery or battery-backup carbon monoxide alarms (UL 2034) near every sleeping area.

What we would plan for your house.

Before you buy a generator, get your heating system's real electrical numbers: running watts at cold temperatures, minimum circuit amps, starting current, and whether it has heat strips. We can pull those from your equipment's spec sheets so your electrician sizes the generator and transfer switch correctly the first time. If you are replacing your system anyway, an inverter heat pump or a dual-fuel setup makes outage planning much easier. Cold-climate heat pumps also keep their full heat far below a Vancouver winter.

Questions about your system? Call us at (360) 838-5568.

Questions homeowners ask.