Using a generator in winter: cold starts, furnace power, snow and carbon monoxide

Winter outages are often the most dangerous kind. Ready.gov notes that winter storms raise the risk of hypothermia, frostbite, carbon monoxide poisoning, and heart attacks from overexertion. A generator can keep your heat running and pipes from freezing, but cold weather adds challenges: hard starting, snow around the unit, and the temptation to run it somewhere sheltered. This guide covers what to know.

What heating systems need from a generator

Almost every modern central heating system needs electricity, even if it burns gas or oil:

• Gas forced-air furnaces need power for the blower motor, the inducer fan, the igniter, and the control board. The blower is the biggest draw, often around 400 to 800 running watts for a typical 1/3 to 1/2 hp motor, with a starting surge.
• Gas or oil boilers need power for circulator pumps, burners, and controls. Each circulator is often 50 to 200 W.
• Oil furnaces add the oil burner motor.
• Heat pumps need a lot more, because the compressor does the heating. Backup electric resistance strips can draw 5,000 to 15,000+ W, more than most portables can supply.
• Electric baseboard and furnaces are resistive and very power-hungry, typically 1,000 to 1,500 W per room heater and far more for an electric furnace.

For gas or oil systems, a modest generator, often 3,000 to 5,000 running watts with other essentials, is usually enough. Heat pumps and electric heat generally need a standby-class generator, or you'll have to heat one room at a time.

Connecting a furnace safely

Furnaces are hard-wired, usually on a dedicated 120-volt circuit with a service switch near the unit. The safe way to run one on a generator is through a transfer switch or interlock installed by an electrician. See transfer switch vs. interlock.

Some people have a furnace "plug-in" conversion installed: a cord and plug, plus a dedicated receptacle, approved by local code and the equipment manufacturer. If you're considering this, have an electrician and your local inspector confirm it's allowed. Never wire a furnace to a generator through a homemade cord or by backfeeding an outlet.

Modern furnace control boards can be sensitive to power quality. If your furnace won't run reliably on a conventional generator, an inverter generator with low THD, or a properly bonded neutral-ground setup per the manufacturer, may solve it. Ask an HVAC technician.

Starting a generator in the cold

Cold engines are harder to start. Tips:

• Use the right oil. Many manufacturers specify a lower-viscosity oil, such as 5W-30, for cold temperatures. Check the oil viscosity chart in your manual.
• Fresh fuel. Stale gasoline is even harder to ignite in the cold. Rotate fuel and use stabilizer.
• Keep the battery charged. Electric-start batteries lose capacity in the cold. Keep the generator on a maintainer, or store the battery somewhere warmer if the manual allows.
• Choke and prime per the manual. Cold starts usually need full choke.
• Exercise the generator monthly through the winter, so you aren't discovering problems during a storm.
• Propane in the cold. Propane vaporizes poorly in very cold weather, especially from small cylinders, which can reduce power. Larger tanks perform better.

Placement in snow and ice

Snow tempts people to put generators in garages or on porches. The CDC is clear: never use a generator inside your home or garage, even with doors and windows open. Use it only outside, more than 20 feet from windows, doors, and vents. In winter:

• Clear a spot before the storm, and keep snow from drifting against the generator's air intakes and exhaust.
• Use a cover designed for operating generators, which shields the unit from snow while keeping airflow open.
• Watch for blocked vents. Snow can block your furnace and dryer exhaust vents on the outside wall, causing CO to back up into the house. Keep them clear too.
• Put the generator on a stable surface, such as a pallet or pad, so it doesn't sink into snow or sit in meltwater.

The winter carbon monoxide spike

Winter combines several CO sources: generators, furnaces, fireplaces, and people trying to heat with ovens or grills. Ready.gov warns never to heat your home with a gas stovetop or oven, and to use generators and grills only outdoors. The CDC recommends battery-operated or battery-backup CO detectors near every sleeping area, and replacing detectors on the manufacturer's schedule or every five years.

Know the symptoms: headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion. If your CO alarm sounds, get everyone outside and call 911.

Protecting pipes

If you can't keep the whole house heated:

• Keep the heat running at a lower setting, such as 55°F, rather than off.
• Open cabinet doors under sinks on exterior walls.
• Let faucets drip slightly if the house is getting cold.
• Know where your main water shutoff is, in case a pipe bursts.
• If you leave, consider draining the plumbing.

A winter outage plan

1. Before winter: test the generator, change the oil to the winter grade, stock fuel, and confirm your transfer switch includes the furnace circuit.
2. Before a storm: fuel the generator and stage it in its outdoor spot, covered. Clear paths for refueling.
3. When power fails: start the generator, then turn on the furnace circuit first, then the refrigerator and essentials.
4. During the outage: clear snow from the generator and vents, refuel in daylight once the generator has cooled, and check CO alarms.
5. After: let the generator cool, refuel, and service it before storing.

Fuel in winter

Plan for longer runtimes in winter. Heating loads run longer than summer loads, and outages after ice storms can last days. Store enough fuel for at least a few days of your planned run schedule, rotate it, and keep cans somewhere you can reach without shoveling a path in a blizzard.

Avoid overexertion

Ready.gov notes that winter storms bring a risk of heart attacks from overexertion. Moving heavy generators and fuel cans through snow is strenuous. Plan ahead: stage equipment before the storm, use wheels or a sled, and get help if you need it.