Is this enough combustion air

Is this enough combustion air for a water heater and furnace?

Thanks! for your input.

Absolutely not.

Write it up.

At a minimum…a louvered door is recommended.

Thanks! David,

I did just that. Funny thing it was built that way 11 years ago.

Combustion air calculating.

sure it is if you don’t want to light the hot water tank or use the furnace…now if you want to use either of those things you need to remove that door or provide a louver door as the minimum acceptable amount of ventilation…imho…jim

This will help:

It would appear to be an inadequate C/A design.

Knowing the capacities of the Furnace & Water Heater will help in sizing of the openings, but just as important is the location of the openings.

You should always have adequate openings in a high & low design, preferably opposite walls or corners.


Was it direct vent by chance? If so, it get’s its air from outdoors.

I don’t see how anyone can answer the question from the picture without knowing the type of furnace and water heater (source of combustion air), the total BTUs for them, and the cube of the room behind the door. What if that room leads to a large utility room? Let’s not assume it is just a closet.

The question was if this sole supply of air is enough for the mentioned applications and it isn’t. The question did not refer to any other source of air supply.


Are those mechanicals (in that closet) high efficiency?

maybe they are electric

Even if combustion air is from the vent on the wall, then combustion air will also come from the room/closet . You can not assume by only seeing a door that the room or closet is not large enough to support the furnace and water heater. There was no mention of a closet or room in the initial question. Can anyone tell what is behind a closed door by seeing a door? I don’t think it is wise to assume things when inspecting.

Well said.

We simply were not given enough information to make any reasonable determination.

There were not high efficiency or electric. I could not found another source of combustion air. Homeowner had recently finished the basement.

As I understand THE question…Buck asked if this opening is enough combustion air for A furnace and water heater.

  • I am assuming Buck has determined that the equipment is gas fuel rather than electric.
  • I am assuming he has determined that the equipment is installed within a constructed closet or small room.
  • I assume we are assuming a lot of extraneous “what ifs” for conversation sake.

I’m going to give Buck some credit for determining the basics before asking his question.


“Combustion air (“make-up air”) is required for gas burning appliances at a rate of 50 cu ft / 1000 BTU or else external ventilation is required. Due to the room size, that requirement may not be met (formal sizing calculations were not conducted). External ventilation openings should be within 12 inches of the top of the enclosure, and one within 12 inches of the bottom of the enclosure. Inadequate supply of combustion air results in incomplete combustion; products of incomplete combustion include carbon monoxide. The room housing the appliance(s) may be inadequately ventilated for the purposes of providing combustion air and we recommend an evaluation and repair by a licensed plumbing or HVAC contractor.”