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Another Way to Prevent Your Garage from Making You Sick


If you have an attached garage where you live, the odds are high that your indoor air quality is worse than a home without an attached garage. Just take a look at the photo below to see some of the sources of pollutants that can get into your home’s air. How many do you see?

If you have an attached garage where you live, the odds are high that your indoor air quality is worse than a home without an attached garage. Just take a look at the photo below to see some of the sources of pollutants that can get into your home’s air. How many do you see?

Even without zooming in, I can spot five significant sources. The car is the biggest, of course. Every time it drives in or out, exhaust, including carbon monoxide, from the tailpipe enters the garage. On the left you can see a lawn mower and next to it a gasoline container. In the back is a gas water heater (in this case a direct vent type, which is a safer model than the standard natural draft type). To the left of the water heater are shelves full of various things, which may well include pesticides, fertilizers, and other stuff you don’t want to breathe.

Ventilating the garage

So the typical garage has a lot of bad stuff in it. You may not notice the smell in your own garage because you grow used to it after a while, but I often notice a toxic odor in garages. What can you do to keep that stuff out of the air in your home? The first step, of course, is to isolate the garage from the house as well as possible. (See the related articles list below for information on how to do that.)

There’s another thing you can do to keep that garage out of the house, too. Ventilate! With an exhaust fan in the garage, you can do two things to improve your indoor air quality. First, when the fan runs, it removes pollutants from the garage air and sends them outdoors.

Second, the exhaust fan puts the garage under a negative pressure. That way, when you open the door between the garage and the house, air is more likely to flow from the house to the garage rather than from the garage to the house.

Controlling the garage ventilation

You’ve got a few options here. You could set it up to run continuously, of course. If you’ve got a lot of nasty, offgassing stuff out there and you really don’t want to get rid of it…well, my question to you is why the heck not? Build a shed out back. If you’ve already got a shed that’s stuffed to the gills, you could do like Arthur “Two Sheds” Jackson and think about getting a second one.

Rather than running the garage exhaust fan continuously, you could install a switch in the garage and control it manually. That’s not a great solution, though, because it often won’t be running at the time you need it to run. Say you drive into the garage, the overhead door closes behind you. You’ve trapped some pollutants in the air but you have to get out of the car and turn the fan on before it starts removing them.

The best solution, in my opinion, is to use a controller like AirCycler’s GarageVent. When you install it, sensors wired into the doors will turn the exhaust fan on whenever a door to the garage is opened. Then the fan runs for a set amount of time (0 to 2 hours) after you close the door. You can also set it to run based on temperature. Check it out.

Complicating factors

Having said all that, installing a garage exhaust fan may or may not solve your problems. Here are some things that might negate or reduce the effectiveness of your fan, or even cause more problems.

  • Natural draft water heater in the garage. These things can backdraft easily so if you install a large enough exhaust fan, you may end up putting more carbon monoxide into your garage, which could stick around after the fan goes off.
  • Heating and air conditioning system in the garage. It’s not allowed by code anymore, but you could have this setup if you live in an older house. It’s possible that the HVAC system could be sucking up more air than your exhaust fan and sending a lot of contaminants right into your home.
  • Heating and air conditioning vents in the garage. See my previous article on this topic.
  • Negative pressure in the house. Some HVAC systems have unbalanced duct leakage that leads to negative pressure in the house. Some homes have really big exhaust fans. There could be a lot of stack effect. A number of causes could result in the house pressure being more negative than the garage. The garage exhaust fan does help reduce the pressure difference, but the end result may be more contaminants inside the home.

As always, the devil’s in the details so make sure you either understand what’s going on and can measure the effect of a garage exhaust fan or you hire a pro who does and can.

Now, where do you think you’ll put that second shed?


Related Articles

Are You Making These Mistakes with Your Garage?

Want Bad Air? Put a Heating & Cooling System in Your Attached Garage 

I-Joists, Attached Garages, and the Air Leaks That Poison


Photo of garage by Rubbermaid Products from, used under a Creative Commons license.


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This Post Has 6 Comments

  1. There’s also source control
    There’s also source control concerning pollutants in a garage. Electric lawn tools (including mower) instead of gas powered. Carefully evaluate all the nasty stuff on the shelf and see if non-toxic equivalents are available, or if an alternate people friendly method of getting a particular solution’s task done is possible. Heat pump water heater vs. combustion.

    As for the vehicle, an EV would take care of that nicely and may be the norm at some point in the future. But for now with most garages still housing ICE (internal combustion engine) vehicles, I agree that providing a good air barrier between house and garage is the best defense against all of the above, if you can’t eliminate all hazards via source control. Leaving the garage door open after parking is one choice for dispelling auto exhaust but is something most people do not want to do since it leaves their belongings in the garage exposed to passerby.

    Architecturally, carports rule and garages drool. 🙂 Why? I can always park my car in the carport because it is clutter free! I dare not leave any stuff sitting out there…it might not hang around if I do! Annddd…carports decouple the vehicle storage spot from the house. A carport with storage closets included is even better.

    1. Yes, indeed. Carports and
      Yes, indeed. Carports and detached garages are much better for indoor air quality.

  2. Thanks for “venting&quot
    Thanks for “venting” attached garage health problems, article was well “shed”.
    We strongly believe in air sealing common walls, ceilings cantilevered (can’d leave her) unsealed or uninsulated over garages. But,the attached common wall and entry door, needs to be well weatherstripped, (not so common) just like common sense, is not so common! What the hay,(Bailes of great info) we say- It is ok, if the the overhead or any exterior garage doors, are leaky. Thanks for the info about smart exhaust fans, I am a fan of your smart articles, Thank- you for caring and sharing! (Sorry about my rhyme disease)

    1. Oh, my. I’m at a loss for
      Oh, my. I’m at a loss for words, Dennis. Can I get some of that coffee you were drinking?

  3. Noticed my typo in my
    Noticed my typo in my previous comment, about cantilevers, meant to say “can’t” leave her uninsulated, not “can’d” Can you correct sorry my error!

  4. Concept aired by Collin Olson
    Concept aired by Collin Olson of Energy Conservatory some yrs back: “cascade” ventilation placing the storage for contaminants such as paint etc at garage exterior wall, ventilate storage to outdoors, ventilate garage by way of opening between storage and garage. After tightening garage Collin found that a computer muffin fan maintained constant negative pressure of garage WRT house. Let’s also acknowledge Don Fugler who provided estimate that 60% of garage air contaminants wind up in the house.

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