I have a gas water heater in my garage that i enclosed with bi-fold doors. Since there were bi-fold doors with space on the top and bottom and also in the garage, we didn't install combustion air intakes.

We have now made it a game room with central heat and air flowing inside the garage. Do we have to add combustion air? There is not people there all the time.

  • Is replacing the water heater with a sealed-combustion unit an option? Oct 31, 2019 at 11:43

2 Answers 2


Yes, common sense says so.

Maybe people are not there all the time but combustion happens even when no people are there.

Most times these rules are put in place to avoid consequences like poor combustion or combustion gases building up in poorly ventilated spaces.

Provide the combustion air and be safe.

  • The game room may be large enough but the closet sealing the heater is not with out a vent in the door or a large gap that would look funny to get enough square inches of air. A coaxial vent through the roof is another way to add air while allowing exhaust. This is now required in my area of direct vents are not available. One of the few required upgrades when replacing an existing device.
    – Ed Beal
    Oct 31, 2019 at 15:20

You need 50 cubic feet in the room per 1000 Btu/h, which comes to 250 square feet with an 8' ceiling and 40k BTU. I think a converted 2-car garage will hit that; I don't think a one-car garage will. If you can hit that, you can keep this setup. (Assuming the bi-fold doors have slats to allow for airflow through the door; top and bottom of the door isn't good enough for input air.) It's using room air, but as long as the exhaust is working properly, there's no CO exhaust into the room, and it's not using up all the oxygen. (But put a CO detector in the room, just in case.)

However, this is not allowed in bedrooms, because problems at night are much less likely to be noticed until it's too late. This means this room must not be used as a bedroom, and if you sell, cannot be called a bedroom. (Also, the room is a bedroom if the inspector looks at the room and declares it a bedroom for the purpose of gas appliances.)

The alternate way of doing this is to provide an source of outside air in the closet, and replace the bi-fold doors with an exterior-style door with a threshold. This ensures there's no way to leak CO into the game room.

  • If their is not enough air flow into the closet their will be problems and affect the efficiency of the unit no matter how big the room is because the heater is now in an almost sealed space.
    – Ed Beal
    Oct 31, 2019 at 15:16
  • ...Oh, when I said "bi-fold" doors, I was talking about the kind with slats to enable airflow. If you just got regular closet doors, that's not good enough. Oct 31, 2019 at 18:23
  • Ok I could agree with slats all the ones in my last house were solid , since the op mentioned only the air space at the bottom I figured they were solid.
    – Ed Beal
    Oct 31, 2019 at 22:25

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