Running a Generator in Rain and Snow

Power outages happen in weather. That's the whole problem: the conditions that knock out power are the conditions that make running a generator awkward — and the obvious solution is the one that kills people.

Running a generator in weather

A generator is an internal combustion engine that needs airflow and exhaust clearance. Any cover that traps heat or blocks exhaust creates a fire and CO hazard — which is why the answer is a purpose-made open-sided canopy, not a tarp.

Can you run a generator in the rain?

The generator stays outside, 20+ feet from the building, in any weather.

Not in the garage. Not with the door open. Not in a shed, carport, breezeway, or "just inside out of the rain".

A garage is a partially enclosed space. Carbon monoxide accumulates there and migrates into the house through the connecting door and any gap. This is the single most common fatal generator scenario, and it recurs every storm season for exactly this reason: it was raining.

See generator carbon monoxide safety.

What does weather actually do to a generator?

Water on electrical components. Rain reaching the alternator, control panel, or receptacles creates shock and damage risk. Standing water under a generator is worse.

Snow accumulation blocking cooling intakes and exhaust.

Cold affecting starting, oil viscosity, battery capacity, and propane vaporization.

None of these are solved by moving it indoors.

What cover can you use on a running generator?

The correct answer: a cover or canopy designed for operation — open-sided, with a roof to keep precipitation off, and full airflow around and through the unit.

What makes one acceptable:

• Open sides so cooling air circulates
• Exhaust clearance — nothing near the muffler
• Adequate height above the unit
• Secure in wind

Purpose-made generator tents and canopies exist and are inexpensive relative to the generator. A permanent open-sided structure works too, provided it doesn't enclose.

What is not acceptable: a tarp over the unit, a plastic tote, a homemade box, a doghouse, or anything that restricts airflow or traps exhaust. Every one of these has caused fires or CO deaths.

Elevation and drainage

Get it off wet ground. Standing water under a running generator is a hazard, and it's how water reaches components that shouldn't see it.

Options: a purpose-made stand, concrete pavers, or a raised platform. In snow country, elevate above expected snow depth.

Keep the area drained. Water pooling around the generator is the problem to design out.

Will a generator start in cold weather?

Oil viscosity. Cold thickens oil, making starting harder and delaying lubrication. Manufacturers specify viscosity by temperature range — use the correct grade for winter, and check the manual rather than assuming. Some recommend a lighter oil below a certain temperature.

Battery. Electric-start units lose cranking capacity in cold, and a battery that was marginal in October is dead in January. Keep it charged; consider a maintainer.

Propane vaporizes less readily in cold, and vapor pressure falls further as the tank empties. In deep cold with a nearly empty cylinder, a generator can starve for fuel. Keep tanks reasonably full and prefer larger tanks in winter — more surface area for vaporization. See propane tank sizing for a generator.

Gasoline doesn't have the vaporization problem, which is one situation where it has an advantage.

Some standby generators offer cold-weather kits — block heaters, battery warmers — worth having where winters are severe.

How do you run a generator in snow?

• Clear snow from around and above the unit before and during operation
• Keep intakes and exhaust clear — accumulation blocks cooling
• Watch for drifting, which can bury a unit surprisingly fast
• Elevate above typical snow depth as a matter of design, not response
• Clear the exhaust path — snow banked around a muffler is both a fire risk and a CO risk

For standby generators, snow management around the enclosure is a real winter maintenance item.

Handling it safely in wet conditions

• Dry hands, always
• Never stand in water while operating or connecting
• Inspect cords for damage before use — see generator extension cords and wire gauge
• Keep connections elevated and out of puddles
• Use the GFCI-protected receptacles on the generator for cord-connected loads
• Refuel only when cool, and preferably not in pouring rain where water can enter the tank

Planning ahead

The best time to solve this is before the storm:

• A running cover or canopy on hand
• A designated, drained, elevated location identified — 20+ feet out, exhaust direction planned
• Correct oil viscosity for the season
• Battery charged, propane tanks full
• Cords rated for outdoor use and inspected
• CO alarms tested

Deciding where the generator goes during a storm, in the dark, while wet, is how people end up putting it in the garage.

Where to go next

• Generator carbon monoxide safety
• Generator placement and clearances
• Generator maintenance schedule
• Size it properly: generator sizing calculator

More in our generator and backup power guides.