I am finishing my basement and enclosing my furnace and tankless water heater in an unfinished utility room. Both the furnace and tankless water heater are direct-vent systems pulling air from the outside. Do I still have to put in the 2 vents (1 high and 1 low) in the walls for combustion air? It's a 60,000 BTU input furnace.

  • What codes apply in your area? Commented Feb 17, 2018 at 14:41
  • All I can find are codes for when it's not a direct vent system. If it's not direct vent, they say 1 vent within 12" of ceiling and 1 vent within 12" of floor. 1 sq in per 10,000 BTU so each vent needs to be 60 sq in. But then I saw another post where min vent size is 100 sq in. Really hard to find the exact code words for Howard County Maryland. But nowhere does it say if you have direct vent then you don't need extra venting.
    – Ken Goetz
    Commented Feb 18, 2018 at 0:03

1 Answer 1


To my knowledge there is no code requirement that the room be vented with high efficiency direct vent appliances. As you said, both systems provide their own combustion air from outside the building envelope.

However, it's likely that a tightly enclosed room will get quite warm at times. You may want to provide a means for heat escape.

  • Good point about getting possibly warm. So maybe it wouldn't hurt to put one vent on the wall near the ceiling.
    – Ken Goetz
    Commented Feb 17, 2018 at 23:57

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