How to Safely Use a Generator: Avoid CO Poisoning and Fire Risks

A portable or standby generator can keep your furnace, sump pump, and refrigerator running when the grid fails. But the same combustion engine that produces electricity also produces carbon monoxide (CO), a colourless and odourless gas. Every year in Canada, people are poisoned by generators used too close to a home or inside a garage. Before you start any unit, treat generator safety as part of your home backup plan, not an afterthought. Our best home backup power guide covers how to match a unit to your actual outage needs, but every setup must follow the basic CO and electrical rules here.

Most generator injuries are preventable. The two big hazards are carbon monoxide and electricity. CO exposure can permanently damage the brain or kill within minutes at high concentrations. Electrical mistakes like backfeeding can injure utility workers or start a fire inside your walls. The rules from Health Canada and the CSA Group are not optional, they are the minimum standard. This guide applies to portable gas, propane, and inverter generators, as well as larger standby units installed by an electrician.

Ontario homeowners face specific risks during ice storms and summer thunderstorms. When the power goes out for hours or days, people often move a generator closer to an open window or under a porch to keep it dry. That instinct kills. A safer setup takes a few extra minutes and costs less than $100 in basic accessories. If you are buying a new portable unit, our best portable generators comparison includes runtime and fuel consumption details. Still, even the best generator is dangerous without these steps.

This article is written like a field guide from an electrician who has responded to outage damage. You will learn exact placement distances, CO detector rules, cord sizing, refuelling steps, and Ontario code basics. We also link to authoritative sources, including CSA Group standards and Health Canada exposure limits. Read it before you start the engine. Then keep it near your generator manual.

What You’ll Need

• CSA/UL-listed battery-powered CO detector
• Outdoor-rated 12-gauge or 10-gauge extension cord
• Approved fuel container with flame arrestor
• Dry chemical fire extinguisher
• Purpose-built generator cover or canopy
• Non-contact voltage tester and transfer switch if connecting to panel

How Do You Safely Use a Generator?

1. Place the generator at least 20 feet away from all home openings

Place the unit on a flat, level surface at least 20 feet (6.1 metres) from every door, window, vent, soffit, and crawlspace opening. A running engine discharges carbon monoxide in a concentrated plume. Wind can push that plume through a small crack faster than many people realize. The 20-foot rule is not a suggestion; it is the minimum distance recommended by Canadian safety authorities and fire services.

Keep the generator away from attached garages, carports, decks, porches, and covered patios. Even an open garage door does not provide enough ventilation because CO can rise, swirl, and seep into the house through the door seal or adjacent wall. The engine exhaust can also reach temperatures above 260 degrees Celsius. That heat can melt vinyl siding or ignite dry grass if the unit sits too close. Place the unit on concrete, packed gravel, or bare soil, never on a wooden deck.

Imagine a line between the generator’s exhaust outlet and your home. If possible, direct the exhaust away from the house and away from any neighbouring windows. Check the wind direction before the engine starts. That said, do not move a running generator once it is under load. Shut it down, reposition it, and start again. If you are using a portable unit during an Ontario ice storm, snow can drift and block the exhaust. Clear a radius around the unit and keep it visible. The CSA Group’s generator safety standards assume that exhaust gases need open air dilution.

2. Install battery-powered CO detectors and check them before every start

Install a certified carbon monoxide alarm on every level of your home and outside every sleeping area. Ontario’s fire code requires CO alarms near sleeping areas in homes with fuel-burning appliances, fireplaces, or attached garages. Look for a CSA 6.19 or UL 2034 label. If you use a generator during an outage, you need a battery-powered alarm or a hardwired unit with battery backup. The alarm must work when grid power is out.

Health Canada has set indoor air quality guidelines for CO at 11 parts per million (ppm) averaged over 8 hours and 25 ppm averaged over 1 hour. For context, a generator exhaust stream can contain more than 100,000 ppm of CO near the discharge. This is why even a few minutes in a garage can be fatal. Concentrations around 800 ppm can cause death within two hours. Symptoms of lower exposure include headache, dizziness, weakness, nausea, vomiting, chest pain, and confusion. If the alarm sounds, get outside immediately and call 911.

Test the CO detector before you start the generator and again after you have been running it for a few minutes. Do not assume a hardwired alarm will help during a blackout. Replace batteries per the manufacturer’s schedule, and replace the detector itself before its expiry date. If you need a new unit, check battery-powered models with digital peak-level displays. Check battery-powered CO detectors on Amazon. The cost is small compared to the risk.

CO is especially dangerous for people who use oxygen or rely on medical devices. If you power CPAP, oxygen concentrators, or dialysis equipment during an outage, review emergency power medical equipment and place a CO detector in the same room as the patient. Low-level exposure can mimic flu symptoms. Do not wait for a visible colour change or smell; CO has neither.

3. Use outdoor-rated cords and never plug a generator into a wall outlet

Use only heavy-duty extension cords rated for outdoor use. For a 15-amp load at up to 50 feet, a 12-gauge cord is the usual minimum. For longer runs or 20-amp and 30-amp generator outlets, move to a 10-gauge cord. A typical 14-gauge indoor cord can overheat, melt, and start a fire when it carries a fridge, freezer, or space heater for hours. Check the jacket for a W marking, which means weather resistant. Check outdoor-rated generator extension cords on Amazon.

Never plug a generator into a wall outlet, also known as backfeeding. This practice sends power backward into your home’s wiring and out to the utility transformer. A line worker repairing the grid can be electrocuted by your generator. Backfeeding also bypasses circuit breakers and can overload your panel or start a fire. The correct way to connect a generator to house circuits is through a manual transfer switch or an interlock kit installed by a licensed electrician.

Before you connect anything, add up the starting and running watts of the devices you plan to power. A fridge may need 700 running watts but up to 2,200 starting watts. A sump pump can pull 1,000 to 2,000 starting watts. Our how to size a generator for your home guide walks through the calculation. Do not guess. A cord that is too thin or a generator that is too small will trip breakers or overheat.

Protect cord connections from puddles, snow, and rain. A generator outlet has high voltage. Keep plugs off wet ground using a dry block or cord lifter. If a cord feels hot, smells like melting plastic, or has a nicked jacket, stop using it. The next step covers refuelling, which is another common moment for fire.

4. Refuel only when the engine is cold and store fuel outside

Shut the generator down and let the engine cool for at least 15 to 20 minutes before you open the fuel cap. Gasoline can ignite on contact with a hot muffler or exhaust manifold. Spilled fuel near a warm engine produces vapours that can flash. Refuelling while the engine runs is extremely dangerous and also risks a fuel spill on moving parts. Use a funnel and keep a dry chemical fire extinguisher nearby.

Store fuel only in approved containers, such as CSA or ULC-listed safety cans, with a flame arrestor and tight cap. Keep gasoline outside the house, detached garage, or shed, never in a basement or near a furnace. Limit the amount you store to what you actually need. A 5,000-watt portable generator burns around 2.5 to 3.0 litres per hour at 50% load. A 10-hour outage may use 25 to 30 litres. Plan storage accordingly.

Fuel quality matters. Gasoline left in a generator carburettor for months can form varnish and make the unit hard to start when the next outage hits. Add a fuel stabilizer if you store fuel for more than 30 days. Propane does not degrade the same way and is often a better choice for occasional use. For detailed runtime and fuel planning, see how long can a generator run continuously.

Place the fuel can away from the generator and away from any ignition source. When you pour, do it slowly and ground the container to reduce static if possible. Wipe up spills and let the area ventilate before starting the engine. Move the fuel container at least 20 feet from the generator before you pull the starter cord.

5. Protect the generator from rain, snow, and wet ground

Water and electricity do not mix. A wet generator can short, deliver a shock, or fail when you need it most. If rain or snow starts while you are running the unit, shut it down before covering it. Use a purpose-built generator cover or a free-standing canopy that keeps rain off while leaving the exhaust open and at least 5 feet of clearance on every side. Never wrap the generator in a tarp like a package. The tarp can block cooling air, trap exhaust, and melt onto hot parts.

In Ontario, winter outages often arrive as freezing rain. Ice can weigh down trees and drop power lines. A generator placed on a frozen puddle or in a snowbank can sink as the exhaust melts the snow, tilting the unit and exposing live parts. Set the generator on a dry, level pad made of pressure-treated wood or a rubber mat. Keep the exhaust outlet pointed away from snowbanks. For more cold-weather outage planning, see our Ontario ice storm power outage prep guide.

If the generator has a grounding terminal, follow the manufacturer’s instructions for grounding. Some portable generators need a ground rod for certain conditions, but most homeowner setups use GFCI-protected outlets. Test the GFCI button monthly. If the ground is wet and you must handle cords or plugs, wear dry rubber-soled shoes and never stand in water.

6. Respect runtime limits and balance the load so the engine does not overheat

Most portable generators are air-cooled. They shed heat through the engine block and flywheel. If you push them at full rated load for hours in summer, they can overheat. A common rule is to run a portable generator at no more than 80 percent of its rated running watts for long periods. Example: a 7,500-watt generator should stay around 6,000 watts running load. This leaves headroom for starting surges from fridges, furnaces, and well pumps.

Starting watts are not the same as running watts. A well pump may draw 2,000 starting watts for a second or two, then settle to 800 running watts. If you connect too many motor loads at once, the generator bogs down and voltage drops. That can damage electronics. Start the largest motor first, wait a few seconds, then add smaller loads.

Check the oil level every time you refuel. Air-cooled engines consume oil. Running low on oil can seize the engine in minutes. Many generators have a low-oil shutdown, but not all. You may need to shut the unit down after 12 to 20 hours of continuous use to check oil, inspect the air filter, and let the exhaust cool. A typical 7,500-watt portable with a 25-litre tank may run 8 to 10 hours at 50% load, depending on brand and elevation.

Do not ignore unusual sounds, heavy vibration, or a burning smell. These are warning signs of overload or mechanical failure. Shut the unit down, disconnect the load, and inspect. If you are running a standby generator, the automatic transfer switch usually handles load management, but you still need annual maintenance from a licensed technician.

7. Shut down the generator the right way and inspect it after every use

Before shutting down, disconnect or switch off the load using the individual circuit breakers on the generator. Let the engine run without load for two to three minutes. This cool-down period helps the alternator and exhaust system stabilize. Then turn the engine switch to off and close the fuel valve if your model has one. Never yank the spark plug wire or turn off the fuel valve while the engine is under load.

Inspect the unit after it cools. Look for frayed cords, cracked fuel lines, loose battery terminals on electric-start models, and any signs of melted plastic near the exhaust. Check the oil level and colour. If the oil looks dirty or smells burnt, change it before the next outage. Clean the air filter if it has visible dust. A neglected generator is the one that fails at 2 a.m. during a week-long outage.

Store the generator in a dry, ventilated shed or garage with the fuel tank either full with stabilizer or drained, depending on the manufacturer. Do not store gasoline in a generator near a furnace, water heater, or any pilot light. Cover the unit with a breathable cover to keep dust off but allow moisture to escape. If you expect a multi-day grid failure, plan for maintenance in advance because service shops may be closed.

8. Get a permit and use a licensed electrician for standby generators and transfer switches

A portable generator connected to your home electrical system requires a transfer switch or interlock device. Under Ontario rules, this is not a DIY project. The Electrical Safety Authority (ESA) requires a licensed electrical contractor to pull a permit and inspect the final connection. A transfer switch isolates utility power from generator power, preventing backfeed and protecting the grid. An interlock kit is a less expensive manual option, but it must be listed for your exact panel and installed to code.

Standby generators are treated as permanent electrical installations. They need a permit, electrical inspection, and proper gas connections. Only a licensed gas fitter or TSSA-registered contractor should connect natural gas or propane lines. Unit placement must meet setbacks from windows and property lines and must respect noise limits. A permanent unit can be a good long-term solution, but it is not a weekend project.

Many Ontario homeowners are choosing battery backup instead of a generator for shorter outages or for silent overnight use. A correctly installed battery system needs no fuel and produces no CO. Still, for long outages during an ice storm, a generator often remains the most practical primary source. The safest system may be a hybrid: generator plus battery.

You do not need an electrician to use a portable generator with extension cords. But you do need them for any connection to your panel. Any permanent wiring, transfer switch, inlet box, or subpanel must be inspected by the ESA. Keep a copy of the inspection certificate with your home records. Insurance companies may deny a fire claim if unpermitted electrical work caused the loss.

Red Flags & Warnings

• 🚨 Never run a generator indoors, in a basement, crawlspace, or attached garage, even with the door open. CO builds to lethal levels in minutes.
• 🚨 Never backfeed by plugging a generator into a wall outlet. You can electrocute utility workers and start a fire.
• 🚨 Never refuel a hot or running generator. Shut it down and wait 15 to 20 minutes for the engine to cool.
• 🚨 Do not use a household extension cord that feels warm or looks worn. Use only outdoor-rated 12-gauge or heavier cords.
• 🚨 Do not ignore symptoms like headache, dizziness, or nausea while a generator is running. Get outside and call 911.
• 🚨 Never leave a portable generator running in rain or snow unless it is covered by a purpose-built canopy with open ventilation.

Frequently Asked Questions

What Should You Remember?

• Placement is the single most important safety step. Keep every generator at least 20 feet from all home openings.
• CO alarms must be battery-powered and tested before each generator start. One alarm per level, outside sleeping areas.
• Cords must be outdoor-rated and 12-gauge or heavier. A thin cord can overheat and start a fire.
• Backfeeding is deadly and illegal. Use a licensed electrician and transfer switch for panel connections.
• Refuelling happens only after a 15 to 20 minute cool-down. Store fuel outside in approved containers.
• Wet weather demands a purpose-built canopy or generator tent. Never wrap the unit in a tarp.
• Maintenance before storage keeps the generator reliable for the next outage. Check oil, fuel, and cord each time.

This article is for general information only. Always follow manufacturer instructions, local electrical codes, and hire a licensed electrician for transfer switches and standby generator installation. Carbon monoxide is deadly , never run a generator indoors.