How to Winterize Your Generator

A homeowner walkthrough for fall generator winterization: oil and filter, spark plug, battery, fuel stabilizer, cold-weather start procedure, snow shelter, and the run-and-store vs store-empty tradeoff.

Pair with the Generator Fuel Runtime Calculator, the Fuel Stabilizer Dosage Calculator, the how much fuel should you store for a power outage guide, and the how to prepare for a power outage anchor guide for the broader fall prep system. Working on the rest of the home in parallel? See the Water Heater Flush Frequency Calculator and the how to read your thermostat correctly guide.

Quick steps

Run the generator under load. 15 to 30 minutes circulates oil and reveals starting issues while you have time to fix them.
Change the oil and filter. Hot drain catches more contamination; refill with synthetic 5W-30 for cold climates.
Inspect spark plug and battery. Spark plug every 100 hours or 2 years; electric-start batteries lose 30 to 50 percent of cold cranking power.
Stabilize fuel or run dry. Add stabilizer and run 5 to 10 minutes, OR drain tank and run carburetor empty.
Cold-weather start kit. Block heater (electric-start models), oil-pan heater, or move generator to an unheated shed.
Plan a snow shelter. Generac GenTent or similar UL/CSA-certified cover; 20 feet (6 meters) from doors and windows.
Set monthly exercise reminder. Run under load 15 to 30 minutes monthly through winter to keep the unit ready.

Schedule winterization 2 weeks before overnight lows reach 32 F (0 C) in your area.

For US Midwest and Northeast, that’s mid-October to early November. For Canadian prairies (Manitoba, Saskatchewan, Alberta) and Quebec, late September to mid-October. Coastal Pacific and US South have a longer window through November.

What you’ll need

Owner’s manual. Capacities, oil viscosity, spark plug part number, valve clearances. Keep a digital copy in your phone.
Synthetic oil for cold climates. 5W-30 synthetic for winter use down to minus 20 F (minus 29 C). 0W-20 for very cold prairie winters. About 0.5 to 1 quart (0.5 to 1 L) for most portable generators.
Oil filter (if applicable). Many small portable generators do not have a replaceable filter; larger 6,000+ watt models do. Match the part number from the manual.
Spark plug. NGK, Bosch, or Champion equivalent of the OEM. About 5 to 12 dollars each.
Fuel stabilizer. Sta-Bil (red) or PRI-G are the most common. 1 oz (30 mL) per 2.5 gallons (9.5 L) of gasoline; the Fuel Stabilizer Dosage Calculator sizes for any tank.
Battery tender (electric-start models). 1 to 2 amp trickle charger, about 30 to 50 dollars. Plugs in to maintain the starter battery through winter.
Snow shelter or generator cover. Generac GenTent (200 to 300 dollars), IPower Storm Bonnet, Champion Storm Shield. Look for UL (US) or CSA (Canada) certification.
Carbon monoxide detector for the storage area. Cheap insurance if the generator runs anywhere near the house. Use the Carbon Monoxide Detector Placement guide for placement.

Pre-winter inspection

Five mechanical items deserve a look before any fall storm. Catching a worn part before a power outage costs 30 minutes; catching it during one costs much more.

Oil and filter. Drain hot oil into a pan, replace the filter, refill with the right viscosity for your climate. Synthetic 5W-30 down to minus 20 F (minus 29 C); 0W-20 for prairie or interior-Canadian conditions; 10W-30 fine in milder regions.
Spark plug. Pull and inspect every 100 hours or 2 years. Light-tan center electrode is healthy; black and oily means the engine is running rich; white and crusty means lean. Re-gap or replace per the manual.
Air filter. Tap out dust on a foam pre-filter; replace the paper element if dark and caked. Clogged air filter is a common starting-trouble cause.
Battery (electric-start models). Disconnect, terminal-clean, charge to full, reconnect. A 30 to 50-dollar battery tender plugged in through winter handles this automatically.
Cooling fins and exhaust shielding. Brush off dirt, leaves, and any wasp nests from the engine cooling fins. Look for cracked or rust-burned spots on the muffler shielding.
Wheel kit and frame. Tire pressure, axle pin, frame welds. A flat tire on a 200-pound generator becomes a moving problem on dirt or snow.

Confirm runtime against your fuel stockpile with the Generator Fuel Runtime Calculator and dose stabilizer with the Fuel Stabilizer Dosage Calculator.

Stabilize fuel or store empty

Two valid winterization paths. Pick one based on storage duration and humidity, not personal preference.

Run-and-store with stabilizer (default for most users). Add stabilizer at the dose printed on the bottle (typically 1 oz / 30 mL per 2.5 gallons / 9.5 L). Run the generator 5 to 10 minutes so the treated fuel circulates through the carburetor and fuel lines. Store with full tank to minimize internal condensation. Stabilized gasoline lasts 12 to 24 months. Use this for typical 4 to 6-month winters in heated or covered storage.
Store empty (best for long storage and humid climates). Drain the tank into a clean fuel can, then run the engine until it stops on its own. Pull the bowl drain on the carburetor (if equipped) to remove the last residue. Cap the fuel inlet. Use this for storage longer than 6 months, ethanol-blend gasoline regions, or coastal humid environments.
Avoid mixing E10 ethanol gasoline with long storage. Ethanol absorbs moisture from the air, leading to phase separation that ruins fuel and corrodes the fuel system. If your local pumps are E10 or E15, prioritize either short storage with stabilizer or full empty.
Diesel is different. Diesel generators (smaller portables, larger standby units) require a separate diesel-specific stabilizer (PRI-D, Power Service) and biocide treatment. Untreated diesel grows microbial sludge in 6 to 12 months. The Diesel Storage Life Calculator handles dosing.
Propane storage is forgiving. Propane standby generators do not need fuel stabilization; the only fuel-storage step is verifying the tank gauge above 30 percent before storm season. Cold-weather operation does require winter-grade propane (HD-5 grade with low butane content) in coldest regions.

Cold-weather start procedure

Winter starts are harder than summer starts because oil is thicker, batteries are weaker, and gasoline vaporizes less readily. Six tactics keep the unit reliable.

Use winter-rated oil. 5W-30 synthetic down to minus 20 F (minus 29 C). 0W-20 for prairie / Canadian interior winters reaching minus 30 F (minus 34 C). Conventional 10W-30 only above 0 F (minus 18 C).
Battery blanket or trickle charger (electric start). A 30 to 80-dollar battery blanket keeps the starter battery above its rated minimum operating temperature. Trickle charger (battery tender) keeps it at full charge through winter inactivity.
Move to a slightly warmer space if possible. An unheated but enclosed shed (typical 10 to 20 F warmer than outdoor) makes a real starting difference. Garage is also fine for storage but never run the generator in a garage.
Choke fully on cold start. Most carbureted portables need full choke for the first 10 to 30 seconds, then opening as the engine warms. Owner manual specifies the exact procedure.
Pre-warm the engine block on extreme cold days. Below minus 20 F (minus 29 C), an engine-block heater or oil-pan heater (50 to 150 dollars) keeps the engine above the minimum starting temperature.
Pull-start technique in cold. Slow steady pull, not a yank; let the recoil retract fully. Cold pull-start mechanisms can crack the recoil rope; warming the unit by a few degrees first reduces breakage risk.

Snow and ice enclosure

Generators must run outdoors. They also need protection from rain, snow, and ice. The right shelter solves both.

Use a manufactured generator cover. Generac GenTent (about 200 to 300 dollars), IPower Storm Bonnet, Champion Storm Shield. Sized for the unit, allows airflow, exhaust passes through. UL (US) or CSA (Canada) certification on the box.
Position 20 feet (6 meters) from any door, window, or vent. Carbon monoxide leaks back through any gap. The 20-foot rule is FEMA standard; CSA and UL technical guidance is similar.
Never use a tarp. Tarps trap exhaust, restrict airflow, and can ignite from hot exhaust components. Manufacturer covers and sheds are airflow-engineered.
Garage with door open is not safe. CO accumulates faster than the open door can vent, especially in cold weather when the air is denser. Carbon monoxide deaths during outages overwhelmingly trace to garage operation. The Carbon Monoxide Detector Placement guide covers home detector positioning.
Pre-built generator shelters. Some homeowners build a small wooden enclosure (Suncast or shed). Must have full airflow on three sides, exhaust shroud, and 20-foot setback. Permit may be required.
Snow accumulation strategy. After heavy snow, dig out around the generator before starting. The unit needs cold air intake and exhaust clearance. A 24-inch (60 cm) clear perimeter is the minimum.

Run-and-store vs store-empty tradeoff

Approach	Best for	Pros	Cons
Run-and-store with stabilizer	4 to 6-month winter, heated or unheated covered storage, non-coastal regions	Fast (15 minutes), simple, generator stays ready for surprise outages	Stabilized fuel still ages; humid climates risk water absorption in E10 gasoline
Store empty (drain and run dry)	Storage longer than 6 months, ethanol-blend gasoline regions, coastal humidity, cottage / seasonal use	No fuel-aging risk; carburetor stays cleaner over multi-year storage	Empty generator cannot start during a surprise outage without first refilling; takes 30 to 60 minutes
Run propane standby	Whole-home backup, premium reliability, frequent outage region	No fuel stabilization needed; weekly self-exercise; CSA / UL certified	Higher upfront cost (4,000 to 12,000 dollars installed); requires permit and gas-line connection

Monthly winter exercise

The single highest-leverage maintenance habit is monthly exercise during storage. 15 to 30 minutes a month catches issues early.

Pick a fixed monthly date. First Saturday of each month is the standard. Calendar reminder. Same routine each time.
Run under load. Plug in a small appliance (lamp, space heater, fan) to 25 to 50 percent of generator capacity. No-load running is less effective at maintenance.
15 to 30 minutes is the standard duration. Long enough to bring engine to full operating temperature, drive off any condensed water in the crankcase, and circulate oil through bearings.
Watch for changes. Hard starts, unusual noises, exhaust smoke color, oil pressure warnings. Note any changes; investigate before the next outage.
Refresh fuel every 12 months. Even stabilized fuel ages. Annual full drain-and-refill is the safest cadence; alternate years also work for short winters.
Standby generators self-exercise. Programmable from the controller; weekly is the standard. Verify it’s enabled.

Track every winterization service alongside the rest of your home seasonal cadence in the Home HVAC Maintenance Log.

Common mistakes

Skipping fall winterization entirely. A generator that sat with un-stabilized fuel through winter typically will not start when needed; gummed carburetor jets are a 100 to 200-dollar shop bill.
Running the generator in a garage. Carbon monoxide kills. 20 feet from doors and windows, outdoors only.
Tarp instead of a real shelter. Restricted airflow, ignition risk, exhaust trapping. A 200-dollar GenTent solves all three.
Wrong oil viscosity for the climate. Conventional 10W-30 in prairie winter conditions causes hard starts and accelerated wear. Synthetic 5W-30 is the all-climate default; 0W-20 for the coldest interior-Canadian environments.
Letting the battery die over winter. Electric-start batteries lose 30 to 50 percent of cranking capacity by spring without a tender. A 30-dollar trickle charger eliminates the problem.
Storing inside the house. Even an empty fuel tank gives off some hydrocarbon vapors. Stored generators belong in a shed, garage, or outbuilding, never in the basement or living space.
Skipping monthly exercise. Generators that sit untouched for 5 to 6 months have a much higher failure rate when needed. 15 minutes a month is cheap insurance.
Buying without UL or CSA certification. Some online imports skip certification entirely. The cost difference is small; the safety and warranty implications are not.

FAQ

When should I winterize my generator?

Schedule winterization before the first sustained freeze. In the US Midwest and Northeast, mid-October to early November is the standard window. In Canadian prairie provinces (Manitoba, Saskatchewan, Alberta) and Quebec, late September to mid-October is more typical because winter arrives sooner. The trigger is roughly two weeks before overnight lows reach 32 degrees F (0 degrees C) in your area. Storm-prone households should finish winterization before the first major fall storm to ensure the generator is ready when needed.

Do I need to drain the fuel?

You have two valid options. Run-and-store-with-stabilizer: add a quality fuel stabilizer (Sta-Bil, PRI-G) to the tank, run the generator 5 to 10 minutes to circulate the treated fuel through the carburetor, then store. Treated gasoline lasts 12 to 24 months. Store-empty: drain the tank and run the carburetor dry, leaving the generator with no fuel inside. Both are valid; run-and-store-with-stabilizer is faster and easier. Store-empty is preferred for storage longer than 6 months or in humid environments where ethanol-blend gasoline can attract water.

What temperature is too cold to start a portable generator?

Most portable generators are rated for operation down to about 20 degrees F (minus 7 degrees C). Below that, oil thickens, batteries lose 30 to 50 percent of their cranking capacity, and pull-start models become physically harder to operate. In Canadian prairie winters and US northern-tier states, generators sometimes need to start at minus 20 F to minus 30 F (minus 29 to minus 35 C). Solutions: switch to a synthetic 5W-30 winter oil, add a battery blanket or oil-pan heater (50 to 150 dollars), and store the unit in an unheated but enclosed space (shed or garage). Standby propane generators handle cold significantly better than gasoline portables.

Is it safe to run a generator in the snow?

Outdoors only, never in a garage or shed even with the door open. Use a steel or fiberglass generator cover or shelter (Generac GenTent, IPower Storm Bonnet, Champion Storm Shield) rated for the unit’s airflow and exhaust. Never use a tarp or improvised cover that blocks airflow or contains exhaust gases. Snow itself is not the problem; carbon monoxide is. Modern shelters are 80 to 250 dollars; many have CSA (Canada) and UL (US) safety certifications. Position 20 feet (6 meters) from any door, window, or vent.

Should I run the generator periodically during storage?

Yes. Even with stabilized fuel, run the generator under load for 15 to 30 minutes once a month. The exercise circulates oil through bearings, drives off any moisture in the crankcase, and keeps the carburetor passages clear. Monthly exercise is the single highest-leverage maintenance task; it catches fuel-system, battery, and starting-circuit problems while you have time to fix them, not during the next outage. Standby generators self-exercise weekly on a programmed schedule; portables need owner action.

What about CSA vs UL safety certification?

In the US, look for UL listing on the generator and any extension cords or transfer switches. In Canada, look for CSA certification (Canadian Standards Association). Both certifications confirm the equipment meets electrical-safety and exhaust-emission standards for residential use. Most major brands (Honda, Generac, Champion, Briggs & Stratton, DuroMax, Westinghouse) sell models certified for both markets, though specific SKUs may differ. When buying, verify the certification on the box before purchase; some online imports skip certification entirely.

Bottom line

Run the generator under load, change oil and filter, inspect spark plug and battery, stabilize fuel or run dry, install a UL or CSA-certified snow shelter, and exercise the unit 15 to 30 minutes monthly through winter. Do this before overnight lows reach 32 F (0 C): mid-October to early November in the US northern tier and US Midwest, late September to mid-October in Canadian prairies and Quebec. Pair with the Generator Fuel Runtime Calculator, the Fuel Stabilizer Dosage Calculator, the how much fuel should you store guide, and the how to prepare for a power outage anchor guide for the broader fall prep system.