Is It OK to Start Your Car in The Garage with The Door Open?

The unforgiving cold of the winter can compel you to run the engine for a few minutes before heading out with your car.

You can let it run in the garage or brave the cold and bring the car outside.

So, Is It OK to Start Your Car in The Garage with The Door Open?

The answer is “no.” No matter how new or “clean” your car is, the engine will produce a significant amount of fumes and carbon monoxide (CO) gas, all of which are toxic. This may sound too obvious but never leave the engine in idle mode with the exhaust pipe facing the wall – at least make sure the tailpipe faces the door whether it’s open or not.

The risk can depend on the weather conditions, the direction of the wind, and whether the car’s tailpipe is facing the wall or the door.

Cold weather increases CO hazards from vehicles

It is estimated that 430 people die of CO poisoning each year in the United States  – about 50000 more seek emergency treatment every year.

Never start your car in the garage in the winter even when the garage door is open. And that’s regardless of whether the exhaust pipe is facing inside or the door.

The cold and dense air of the winter allows the mixtures of smoke particles and CO gas to float around longer and linger in the garage.

Just because you left the door open doesn’t mean the fumes will escape.

The colder the air, the faster these fumes accumulate and the longer they stay in the air.

In sub-zero temperatures, it can take just two minutes for the contaminated air to accumulate to lethal concentrations.

Things can get worse if your garage is attached to your main home – the bad air may find its way into your living space through a channel in the wall or roof.

Of all toxic elements present in the fumes released by the engine, the worst is carbon monoxide gas. It is a colorless, tasteless, odorless, and non-irritating gas produced through incomplete combustion.

When a cold engine is started after several hours, it runs rich.

The catalytic converter – the device tasked with converting the toxic CO gas into a less dangerous CO2 gas – is cold as well and doesn’t complete the conversion as required.

As such, CO concentrations in exhaust fumes can be over 80000 parts/ a million in cold conditions.

This immense concentration ensures that the gas builds up in your garage faster in a short period even with an open door.

Once the vehicle is removed from the garage and the door of the garage is closed, the CO gas remains trapped inside.

You don’t want to be exposed to carbon monoxide.

The gas reduces the red cells’ ability to trap more oxygen essential for your body.

Simply put, CO gas suffocates your system by cutting off the supply of oxygen to all critical organs including the brain, eventually what the medical world refers to as carbon monoxide intoxication.

If the concentration is high enough, such as when the engine is allowed to run for a long time in sub-zero temperatures, CO intoxication may occur in a matter of a few minutes.

Most patients experiencing CO intoxication don’t realize it until it’s too late.

Hot weather lets CO gas escape but isn’t better

During hot weather when the air is hot and breezy, exhaust fumes and CO gas rise rapidly and get carried away into the atmosphere.

This means it’s relatively safe to run the engine behind an open garage door – the fumes are unlikely to linger around the garage long enough to get in your lungs.

However, total safety is not guaranteed more so if you let the engine stay idle for an extended period.

You can’t be certain all the CO gas will escape into the environment.

Still, releasing these fumes into the air comes across as a reckless and environmentally unfriendly thing to do, so don’t do it.

What If It’s A New “Clean” Car?

New cars come with more energy-efficient engines but that’s just that – they are tuned to burn less fuel, not to prevent the production of carbon elements.

Although these so-called “clean” vehicles may produce fewer fumes if left idle in the garage, they can still generate significant levels of CO gas.

Unless the catalytic chamber is exceptionally good at its job, you will still end up with contaminated air.

How To Protect Yourself From Car Generated CO Gas

First of all, avoid idling the engine in the garage.

You know you have been exposed to CO poisoning if you get dizzy and/or feel nausea.

Check the wind direction first if you must leave the engine idle in the garage – shut it down if the wind is blowing directly into the garage.

If you suspect carbon monoxide poisoning, get out into an open area and breathe deeply to take in as much fresh air as possible.

Here Are Some Alternatives To Idling Your Engine:

1. Use the 0W–20 oil which is thinner and was designed for use in cold weather conditions

It is better than typical ‘summer’ varieties of 5W–30 or 10W–30. This oil will make it easier to start your engine in freezing conditions.

2. When it is minus 10 or less outside, use your block heater to warm the engine

The most commonplace design of block heaters entails an incorporated electrical heating element placed in the engine block.

Here Are More Ways To Protect Yourself From CO Gas

  1. Carefully maintain your vehicle including the emission controls, car body, engine, and exhaust system.
  2. Avoid warming up or operating the car in your garage or any other enclosed area. This applies even if the door of your garage is open. Instead, take the vehicle outside and let the engine idle from there.
  3. Never start the car until everyone is inside the vehicle and doors are shut properly.
  4. If you must start the engine while the vehicle is still in the garage, remember to open the door of the garage door first, then back out the vehicle immediately into an open space.
  5. Close the door of the garage thereafter.
  6. The after-effect of idling the engine close by or backing the vehicle out of your garage needs to be monitored closely with a Carbon Monoxide detector installed somewhere in your house.
  7. Some detectors are equipped with memories and LCDs to help you find out if the Carbon Monoxide levels in the house are elevated by the events taking place in your garage.
  8. If the CO gas finds its way into the house, you will need to leave all doors open for about an hour.


So, is it OK to start your car in the garage with the door open? In one word – “No.”

It doesn’t matter how new or “clean” the car is, the engine will produce a significant amount of fumes and carbon monoxide (CO) gas, all of which are toxic.

The cold and dense air of the winter allows the mixtures of smoke particles and CO gas to float around longer and linger in the garage.

CO is a highly toxic gas capable of causing death.