Patio heaters are not safe to use indoors, including in a garage
No. Patio heaters should never run inside a garage, basement, shed, or any enclosed space. Most patio heaters burn propane or natural gas, and they produce carbon monoxide as they operate. In an outdoor patio setting, carbon monoxide disperses into the air. In a closed garage, it builds up to dangerous levels and can kill you in minutes.
Even heaters that seem to work fine outdoors become lethal indoors. A garage with a door cracked open or a small window is still an enclosed space — the carbon monoxide does not clear fast enough. The risk applies to every fuel type: propane tank heaters, natural gas line heaters, and even some electric models designed for outdoor use only.
If you need heat in a garage, you need a heater built for indoor use. The difference is not a minor safety feature — it is a fundamental design difference in how the heater vents exhaust.
Key Takeaways
- Patio heaters produce carbon monoxide, which becomes toxic in enclosed spaces like garages and can cause death within minutes.
- A cracked door or small window does not make a garage safe for a patio heater — the space is still too enclosed for exhaust to disperse.
- Propane, natural gas, and outdoor electric heaters all carry the same indoor risk and should never be used in garages.
- Indoor garage heaters are designed to vent exhaust safely and are the only option for heating an enclosed space.
How patio heaters produce carbon monoxide
Patio heaters work by burning fuel — propane, natural gas, or sometimes wood or charcoal — to create heat. Combustion always produces carbon monoxide (CO) as a byproduct, along with carbon dioxide and water vapor. Outdoors, this exhaust rises and disperses into the open air within seconds. You do not notice it because there is nowhere for it to accumulate.
In a garage, basement, or any enclosed space, carbon monoxide has nowhere to go. It collects in the air you breathe. Even a small patio heater running for 10 to 15 minutes can raise CO levels to dangerous concentrations. The gas is colorless and odorless — you cannot see it, smell it, or taste it coming. By the time you feel dizzy or sick, you may already have breathed enough to cause permanent damage or death.
The Consumer Product Safety Commission (CPSC) and the Centers for Disease Control and Prevention (CDC) both warn against using any fuel-burning outdoor heater indoors. This is not a guideline or a caution — it is a hard rule based on documented deaths.
Why a cracked door or window does not make it safe
Many people think that opening a garage door partway or cracking a window will let carbon monoxide escape. It does not work that way. A garage is still a mostly enclosed space, and carbon monoxide does not disperse quickly enough through a small opening to prevent buildup.
The exhaust from a patio heater is warm and rises, but it does not travel far horizontally before it cools and sinks. If you are working in the garage — especially if you are moving around and breathing harder — you are pulling that exhaust into your lungs faster than it can escape through a crack in the door. You also cannot rely on the door staying open; if it closes even partway, the risk jumps when ready.
Garages are also often connected to living spaces through a door or wall. Carbon monoxide can seep into your home, putting family members at risk even if they are not in the garage itself.
What happens if you run a patio heater in a garage
Carbon monoxide poisoning happens in stages. At low concentrations over a long time, you might feel a mild headache or fatigue and assume you are tired. At higher concentrations, you experience dizziness, nausea, confusion, and chest pain. At very high concentrations, you lose consciousness and stop breathing.
The danger is that carbon monoxide binds to hemoglobin in your blood more strongly than oxygen does. Your body cannot tell the difference, so your cells are starved of oxygen even though you are breathing. This can cause brain damage or death even if you survive the initial exposure.
Some people run patio heaters in garages for years without incident and assume it is safe. That is survivorship bias — they got lucky, not because it was safe. Others have died, and their families did not get to make that assumption.
Indoor heaters designed for garages and enclosed spaces
If you need to heat a garage, basement, or workshop, you have several options that are actually safe. The key difference is that indoor heaters are designed to vent exhaust safely or to produce no exhaust at all.
Electric heaters produce no combustion byproducts and are safe in any enclosed space. Portable electric space heaters, wall-mounted units, and ceiling-mounted heaters all work in garages. They cost more to run than fuel-burning heaters but carry zero carbon monoxide risk. Look for models with a thermostat and an automatic shutoff if they tip over.
Propane heaters with proper venting exist for indoor use, but they are rare and expensive. They require a vent pipe that runs to the outside, similar to a furnace or water heater. If you want a propane heater in a garage, this is the only safe option — and it requires professional installation.
Natural gas heaters can be installed in a garage if they are connected to a gas line and vented to the outside. Again, this requires professional installation and is not a portable solution.
Infrared heaters designed for indoor use are another option. Some use electricity, and some use propane with proper venting. Check the label to confirm it is rated for indoor use in an enclosed space.
The cost difference between patio and indoor heaters
A basic propane patio heater costs $150 to $400 and heats an outdoor area. An electric space heater for a garage costs $50 to $200 and heats an enclosed space safely. A permanently installed propane or gas heater with venting costs $1,000 to $3,000 plus installation.
The cheapest option is usually an electric space heater. It uses more electricity than a fuel-burning heater would use fuel, so your electric bill will go up. But the upfront cost is low, and there is no risk of carbon monoxide poisoning.
If you already own a patio heater and want to use it, do not move it indoors. Sell it or keep it for outdoor use only. Buying an indoor heater is cheaper than a hospital visit or a funeral.
What to do if you have been exposed to carbon monoxide
If you feel dizzy, nauseous, or confused while using a heater in a garage, leave the space when ready and go outside. Get fresh air for at least 15 minutes. If the symptoms do not go away, call 911 or go to an emergency room and tell them you may have been exposed to carbon monoxide. Doctors can test your blood and treat you if needed.
If someone in your home has been exposed and is unconscious, call 911 when ready. Do not move them unless they are in when ready danger. Paramedics are trained to handle carbon monoxide poisoning.
After any exposure, have your garage checked for the source of the problem. If you were running a patio heater, stop when ready and do not use it indoors again.
Frequently Asked Questions
Can I use a patio heater in my garage if I leave the door open?
No. An open door does not provide enough ventilation to prevent carbon monoxide buildup. The gas collects faster than it can escape through an open door, especially if you are moving around or the door closes partway. The only safe option is an indoor heater.
What about electric patio heaters — are those safe indoors?
Some electric patio heaters are safe indoors if they are designed for indoor use and labeled as such. Check the manual or product label. Most outdoor electric heaters are not rated for enclosed spaces and should stay outside. When in doubt, buy a heater specifically labeled for indoor garage use.
How long does it take for carbon monoxide to become dangerous?
It depends on the heater size, the garage size, and how well sealed the space is. A small patio heater in a large garage with a door cracked open might take 20 to 30 minutes to reach dangerous levels. A larger heater in a small, sealed garage could reach dangerous levels in 10 minutes or less. Do not rely on time — use an indoor heater instead.
Is it illegal to use a patio heater in a garage?
Many cities and counties have building codes that prohibit fuel-burning heaters in enclosed spaces. Even if your area does not have a specific law, using a patio heater indoors is extremely dangerous and could result in liability if someone is injured. Check your local building code, but the real reason not to do it is that it can kill you.
What if I only run the patio heater for a few minutes?
Carbon monoxide can reach dangerous levels in minutes, not hours. Even a brief use of a patio heater in a garage is unsafe. If you need heat, use an indoor heater designed for that space.