My fireplace is direct vent, and my gas heater is not. If I replace my gas heater with a direct vent model, do I still need to supply make-up air? The only other gas-burning appliance is a gas stove, upstairs, with a circulating range hood (does not exhaust out of the home).

If I no longer need make up air, I can terminate the direct vent gas heater at the location currently being used for make up air (assuming I meet required code clearances).

  • I doubt it would be code to remove the makeup air supply. heaters produce a higher level of carbon monoxide the vent provides a way to get that out of the living space. I had a friend and her 2 dogs die from carbon monoxide a few years back nothing to mess with.
    – Ed Beal
    Jan 16, 2017 at 14:14
  • 2
    My home has direct-vent furnace and water heater from initial construction, and I have no makeup air duct. I suspect it's not needed, but I'd have an HVAC contractor have a look at your home as a system.
    – isherwood
    Jan 16, 2017 at 14:46
  • @EdBeal Direct vent appliances have an exhaust and a combustion air intake. So a separate "make-up" air vent is likely not required. The danger comes if you have a cracked heat exchanger, but properly functioning CO detectors should catch that failure.
    – Tester101
    Jan 16, 2017 at 15:50
  • I don't do much heating, with the combustion air supplied there should be no need for a vent. Thanks Tester.
    – Ed Beal
    Jan 16, 2017 at 17:33

1 Answer 1


There's no air to "make-up", so likely no need for a "make-up air" supply. However, you'll have to check your local codes to determine if you're still required to have one.

Direct vent appliances will have an exhaust outlet, as well as a combustion air inlet. They draw air in through the combustion air intake, use the air for combustion, then expel the exhaust through the exhaust vent. They should be completely "sealed", when it comes to combustion. They'll also have safety sensors to insure that enough air is coming in, and enough exhaust is going out.

As for the gas range... You'll have to check local codes to be sure, but commonly a range hood that exhaust to the outdoors is required where gas ranges are used. If this is the case, you'll need some way to replace the air that's exhausted by the range hood. If the home is not sealed up really tight, leaky windows, doors, and other openings should provide enough air. Though if the house is sealed well, you'll need to provide an intake vent.

Again, you'll have to check with your local building department, as codes can vary from place to place.

  • Thank you! I really appreciate your involvement in the DIY community. As a bonus question, do you know if exhausting a bathroom fan ~32" away from a direct vent gas appliance is permitted? Neither the bathroom fan installation instructions nor the furnace instructions answer this. Jan 16, 2017 at 19:32
  • @MinnesotaDIY I'll have to look up the exact distance between mechanical ventilation and air intake, as I don't know it off hand.
    – Tester101
    Jan 16, 2017 at 20:46
  • @MinnesotaDIY International residential code has this to say about exhaust opening separation. M1506.3 Exhaust openings. Air exhaust openings shall terminate not less than 3 feet (914 mm) from property lines; 3 feet (914 mm) from operable and nonoperable openings into the building and 10 feet (3048 mm) from mechanical air intakes except where the opening is located 3 feet (914 mm) above the air intake. Openings shall comply with Sections R303.5.2 and R303.6.
    – Tester101
    Jan 17, 2017 at 14:07
  • So the bathroom exhaust has to be 10' away, unless it's more than 3' above the intake.
    – Tester101
    Jan 17, 2017 at 14:08
  • This is great. Again, thank you for volunteering your time to help strangers on the internet with our projects! Jan 17, 2017 at 15:30

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