Quick answer
Cold weather changes how generators start and how fuel behaves. Store fresh, stabilized gasoline. Know that propane pressure drops as temperatures fall. Use the oil grade your owner's manual lists for cold temperatures, keep the battery healthy, exercise the unit regularly, and keep the intake, exhaust, and vents clear of snow. Always run a generator outdoors, away from doors, windows, and vents, with working CO alarms inside. When this guide and your owner's manual disagree, follow the manual.
Who this guide is for
This guide is for homeowners who already have a generator, or are about to buy one, and live somewhere winter brings snow, ice, or long cold stretches. It covers both portables connected by cord or by an inlet and interlock, and permanently installed standby units. If you're still deciding what to buy, start with Portable vs Standby Generators and the Generator Sizing Guide, then come back here to plan for winter.
Why winter is harder on generators
Most generator trouble in winter comes from four things that happen together. Fuel sits longer between uses, so it goes stale or picks up moisture. Engine oil thickens, which makes the starter or your pull-cord arm work harder. Batteries lose cranking strength in the cold. Snow, ice, and drifting can block the air the engine breathes and the exhaust it pushes out. None of these is unusual, and most are prevented with an autumn walkthrough and a simple routine during an outage.
How cold affects each fuel
Gasoline
Gasoline breaks down over time. As it ages it can leave varnish in the carburetor and fuel lines, which is one of the most common reasons a portable won't start after sitting for months. Partly empty containers and tanks can also collect condensation as temperatures swing between day and night.
- Store gas only in approved containers, in a detached shed or other spot your local fire code allows, away from ignition sources.
- Add fuel stabilizer when you fill the container, not months later, and follow the label for how long it protects the fuel.
- Rotate your supply: use older stabilized fuel in your car or mower and refill with fresh fuel on a regular schedule.
- Ask your manual whether to run the carburetor dry or leave it full with stabilized fuel during storage, because manufacturers differ.
Propane
Propane is stored as a liquid under pressure and has to vaporize before the engine can burn it. Vaporizing depends on heat from the air around the tank. As it gets colder, the pressure inside the tank drops and the tank can deliver less vapor. A small cylinder that works fine in mild weather may struggle to keep up with a generator at heavy load in deep cold. Larger tanks have more surface area and hold pressure better, and a fuller tank helps compared with a nearly empty one.
- Keep tanks reasonably full going into winter, and schedule deliveries before the busiest weeks.
- Keep snow cleared from the tank, regulator, and delivery path so the driver can reach it.
- Ask your propane supplier whether your tank size suits your generator and your climate. That's their call, not a guess.
- Never heat a propane tank with a torch, heater, or any open flame.
Natural gas
Natural gas comes through the utility line, so cold doesn't change delivery much at your end, and you don't store any fuel. What matters is whether the line and meter can supply the generator and your furnace, water heater, and other gas appliances at the same time. That's an installer and utility question, settled when the system is designed. In winter, keep snow and ice off the meter and regulator and watch for anything that could damage them, such as falling ice or snow shoveled onto them.
For a wider comparison of fuel types and generator styles, see Home Generator Types.
Winter fuel comparison
| Gasoline | Propane | Natural gas | |
|---|---|---|---|
| Storage | You store it in approved containers; it ages and needs stabilizer and rotation | Stored in a tank or cylinders; doesn't go stale, but tank size and fill level matter | Nothing to store; supplied by the utility line |
| Cold-weather delivery | Flows fine, but stale or wet fuel causes hard starts | Tank pressure falls as it gets colder, so a small tank may not keep up at heavy load | Steady at your end if the line and meter were sized correctly |
| What to watch for | Varnish, condensation, running out mid-outage, safe refueling | Low tank level, snow around the tank and regulator, delivery access | Snow and ice on the meter and regulator, utility supply interruptions |
| Who owns the fix | You (fuel handling and storage) | You plus your propane supplier (tank sizing and deliveries) | Your installer and utility (line and meter sizing); you (clearing snow) |
Oil and cold starts
Cold oil is thick, and thick oil makes an engine harder to turn over and slower to lubricate in its first moments. Your owner's manual lists which oil grades suit which temperature ranges, and many list a lighter grade or a synthetic for cold. Use what the manual says for the lowest temperatures you expect, and change the oil before winter if you're switching grades. Check the level before the season and during long outages, because generators that run for days can use oil. Many units shut themselves off when oil runs low, which is a common surprise mid-outage.
Block heaters, battery warmers, and cold-weather kits
Many standby generators offer an optional cold-weather kit for cold climates. These kits typically include a heater that keeps the engine block or oil warm, and a warmer or pad for the battery. Some manufacturers recommend or require them below a certain climate threshold. Your dealer or installer will know whether your model and region call for one.
A kit adds parts and some install work, so it belongs on the bid. When you collect quotes, ask each installer whether a cold-weather kit is included and why or why not. The Generator Installer Quote Checklist has a spot for it, and Standby Generator Installed Cost explains how add-ons like this affect the total.
Batteries are the most common reason a standby fails its self-test in winter. Most installers suggest checking the battery each year and replacing it on the schedule in your manual or service plan.
Portable vs standby in winter
Standby generators
A standby lives outside all year, so its enclosure, pad, and surroundings matter most.
- Cold-weather kit. Confirm whether you have one, or whether your climate calls for it.
- Enclosure snow. Keep snow cleared from the intake and exhaust louvers. Don't pile shoveled or plowed snow against the unit.
- Drifts and roof runoff. Watch for wind drifting snow against the enclosure and for ice dropping from the roof edge above it. Your installer chooses placement partly for clearance, so let them know if you notice a recurring problem.
- Self-test. Make sure the weekly or biweekly exercise is still running, and notice whether it starts cleanly on cold mornings.
- Service. Book the annual service in autumn, before the busy season.
Portable generators
A portable gets carried out and set up when you need it, often in bad weather and in the dark. The temptation is to put it somewhere sheltered close to the house. Resist that.
- Cover without enclosing. Wet snow and freezing rain can reach outlets and controls. Some manufacturers sell or approve covers or tents that keep precipitation off while leaving the sides open for airflow and exhaust. Use only covers made or approved for your model, never a garage, shed, carport tucked against the house, or tarp wrapped around the unit.
- Placement. Set it on a firm, level spot outdoors, well away from doors, windows, and vents, with the exhaust pointed away from the house. Your manual and local guidance give the distance.
- Cords and inlet. Keep cord connections and the power inlet dry. Use cords rated for outdoor use that stay flexible in the cold, keep connections off the snow, and close the inlet cover when it's not in use. If you're connecting to your home's wiring, it has to go through a transfer switch or interlock, never a back-fed outlet. See Transfer Switch vs Interlock.
- Path. Keep a shoveled path between the door and the generator so you can refuel and check it safely.
Carbon monoxide: placement basics
Generator exhaust contains carbon monoxide, which you can't see or smell. Run a portable outdoors only, never in a garage, basement, crawlspace, enclosed porch, or shed, even with a door or window open. Point the exhaust away from the house and keep it well away from doors, windows, and vents, following the distance in your manual and local guidance.
Install battery-backed CO alarms on every level of your home and near sleeping areas, and test them at the start of the season. Winter deserves extra attention here for two reasons. Snow can block or redirect exhaust, and people tend to keep a generator closer to the house when it's cold and dark. If an alarm sounds or anyone feels dizzy, headachy, or sick, get everyone outside to fresh air and call 911.
Why won't it start in the cold?
| Symptom | Likely cause | What to try first |
|---|---|---|
| Cranks but won't fire; ran fine last spring | Stale or varnished gasoline | Fresh stabilized fuel; if it still won't run, the carburetor may need service |
| Starter turns slowly or not at all | Weak or cold battery | Charge or test the battery; warm storage for portables; battery warmer on standbys if recommended |
| Pull cord is very stiff | Oil too thick for the temperature | Change to the cold-weather grade in your manual |
| Starts, then stalls or surges under load (propane) | Low tank pressure in deep cold or low tank level | Check the tank level; reduce load; ask your supplier about tank size |
| Starts, then stalls or runs rough | Ice or snow restricting the air intake, or a blocked exhaust | Shut it off, let it cool, clear the snow and ice, and restart |
| Standby missed its self-test | Battery, fuel supply, or a controller alert | Check the controller display and the app if you have one, then call your dealer |
| Shuts off after running a while | Low oil shutdown | Check and top up the oil once the engine is off |
If the cause isn't obvious, stop and call a technician rather than repeatedly cranking a cold engine, which can drain the battery or flood it.
Pre-season walkthrough (autumn)
Do this once, before the first hard freeze.
- Read the winter or cold-weather section of your owner's manual.
- Change to the cold-weather oil grade if your manual calls for it, and replace the filter on the manual's schedule.
- Test or replace the battery.
- Confirm the cold-weather kit for standbys, or decide with your dealer whether you need one.
- Refresh fuel: stabilized gasoline in approved containers, propane tank topped off, or the natural gas meter area cleared.
- Run the generator under a light load and confirm it starts cleanly.
- Test CO alarms on every level and replace batteries.
- Lay out cords, the inlet cover, and any approved weather cover, and check them for damage.
- Plan the snow path and where the shovel will be.
- Print your Critical Load Worksheet so you know what you'll power first.
Mid-outage routine
Once it's running, a short routine on a regular schedule keeps you safe.
- Snow check. Each time you go out, clear snow from around the intake, exhaust, and vents, and from any weather cover.
- Refuel safely. Turn the generator off and let it cool before adding gasoline. Never refuel a running or hot engine, and wipe up spills before restarting.
- Oil check. On long outages, check oil at the intervals your manual gives, with the engine off.
- Load check. Stay within your plan. Turning on extra heaters or appliances can overload the unit and is a common cause of stalls.
- Alarm check. Make sure CO alarms are on and working inside.
- Propane check. Watch the tank gauge and call for delivery early if the outage looks long.
Two scenarios (planning outlines)
These are structures to adapt to your home, not recommendations for a specific product or setup.
Scenario 1: Portable on an inlet and interlock, snowy suburb
- Setup. A gasoline portable stored in a detached shed, connected through an outdoor inlet and a panel interlock.
- Before winter. Cold-weather oil grade, battery or electric start checked, stabilized fuel rotated, inlet cover inspected, a model-approved weather cover on hand.
- Placement plan. A level spot outdoors, away from doors, windows, and vents, exhaust pointed away from the house, cord run kept off the snow and as short as practical.
- During an outage. Shovel the path, set up, start it, switch the interlock as your electrician showed you, then load the critical circuits from your worksheet one at a time.
- Routine. Clear snow at every check, let it cool before refueling, check oil on long runs, test the CO alarms.
- Weak points to plan for. Fuel supply over a long outage, and keeping the generator well away from the house on cold, dark nights.
Scenario 2: Propane standby, rural home with a small tank
- Setup. A permanently installed standby on propane with an automatic transfer switch, fed from a smaller tank that also serves the furnace.
- Before winter. Annual service, battery check, cold-weather kit confirmed, tank topped off, and a conversation with the supplier about whether the tank is large enough for the generator and furnace in deep cold.
- Clearance plan. Keep the enclosure louvers, tank, regulator, and driveway clear for the delivery truck.
- During an outage. The generator starts on its own. Watch the controller and the tank gauge, and limit heavy loads in the coldest hours if your installer says the tank may struggle.
- Routine. Clear snow at each check, call for delivery early, watch for any controller alerts.
- Weak points to plan for. Tank pressure in deep cold, and delivery delays after a big storm.
Printable winter checklist
| Item | Done? | Date | Notes |
|---|---|---|---|
| Owner's manual cold-weather section read | ☐ | ||
| Fresh gasoline, stabilized, in approved containers (or propane tank level and size checked, or gas meter area cleared) | ☐ | ||
| Oil grade correct for cold, level checked, spare oil on hand | ☐ | ||
| Battery tested or replaced (standby and electric-start) | ☐ | ||
| Cold-weather kit installed if your model and climate call for one | ☐ | ||
| Self-test or manual exercise confirmed | ☐ | ||
| Spare oil filter and spark plug on hand | ☐ | ||
| Shovel and a clear path to the unit; vents and exhaust clear | ☐ | ||
| Model-approved weather cover only (portables); no enclosing | ☐ | ||
| CO alarms tested on every level and near bedrooms | ☐ | ||
| Outdoor-rated cords checked; inlet cover closes; transfer switch or interlock in place | ☐ | ||
| Critical load list printed | ☐ | ||
| Propane delivery or fuel resupply plan for a long outage | ☐ |
FAQ
Can I run my generator in the garage with the door open?
No. Carbon monoxide can build up and get into the house. Run it outdoors, away from doors, windows, and vents.
Can I put a tarp over my portable to keep the snow off?
Only use a cover made or approved for your model that leaves airflow and exhaust open. Wrapping or enclosing a running generator traps heat and exhaust.
Why won't my propane generator reach full power in deep cold?
Tank pressure drops as the temperature falls, so a small or low tank may not deliver enough vapor. A larger or fuller tank helps. Ask your supplier about sizing.
Do I need a cold-weather kit on my standby?
It depends on your model and climate. Ask your dealer or installer, and make sure every bid says whether one is included.
How often should I start a portable in winter?
Follow your manual's interval, and run it under a light load so the fuel system stays healthy.
Is it safe to refuel while it's running if I'm careful?
No. Shut it off and let it cool first, every time.
Does natural gas work in the cold?
Delivery at your end is usually steady, but your line and meter need to be sized for the generator and your other gas appliances. Keep snow and ice off the meter.