enter image description hereenter image description hereI have attached a picture of my hvac or furnace room with its size. The area has a water heater and furnace which runs by natural gas.

I have planned to have door on both water and furnace side. So installing a Hollow pre hung door to give access to water heater and rest of the space.

However I have a doubt , is this ok to use the hollow/standard door or do I have to have louver door at furnace side, if yes is there any alternative like grill in wall ?

I have already purchased the same door for both the places. Can’t return the door.


  • Usually fossil fuel burning devices need combustion air. They usually get it in modern buildings by having a vent to the outside. Older homes might be leaky enough to not need a special vent to the outside, but closing off the room/space will require vents/grills to the rest of the house of enough size. The picture has not shown yet.
    – crip659
    Dec 19, 2022 at 22:05
  • oh sorry added some pics. thanks
    – PowerTech
    Dec 19, 2022 at 22:42
  • If the proposed door leads to conditioned (heated) space, the combustion air the WH and furnace needs to operate will need to be replaced probably thru bathroom vents or range hoods, meaning you'll have to heat the replacement air. I recently had installed a new furnace and on demand water heater installed (done by pros, not me!) , both had combustion air and of course exhaust to the outside. Dec 19, 2022 at 23:20

1 Answer 1


The gas furnace uses outdoor air for combustion. Those two PVC pipes are an intake of outside air for combustion and an exhaust to the outside for the products of combustion. You should see those pipes outside your house in the vicinity of the utility room. If this is the only fuel-burning appliance in this room, there is no need for louvers.

You didn't say if the water heater is gas or electric. If it is electric, end of story, no louvers needed in the door. If it is gas and it has similar PVC pipes for intake and exhaust, no louvers needed. But if the water heater is gas with a metal flue, you should add louvers to the door so there is always enough air for combustion and free flow of air to maintain a good draft in the flue.

  • Ok thanks , yes I have similar PVC pipe connect to HW. Question. Does HW with metal flue doesn’t vent outside ?
    – PowerTech
    Dec 19, 2022 at 23:49
  • @PowerTech A water heater with a metal flue often goes to a masonry chimney, which is vented outside. However, the gas flame in the base of the water heater with this kind of flue uses room air for combustion. Therefore, adequate ventilation is needed to replace the air that goes up the flue. A louvered door provides that. Fortunately, this is not your situation. Both gas appliances use outdoor air and vent outdoors through sealed pipes. So close the door if you wish, no louvers required.
    – MTA
    Dec 20, 2022 at 2:18
  • Got it thanks..
    – PowerTech
    Dec 20, 2022 at 3:21

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