# Combustion Air

Should there be two vents installed on a door that goes to the room were the furnace is located? If so should there be one on the top and on the bottom and how big should the vents be.

If not cat 4 then One square inch per thousand btu’s should do the trick.
cat 4 furnaces normally draw air from outside through the schedule 40.(best practice)
Yes you want high and low air vents for good circulation.

Oh Bob are you absolutely positive;-):mrgreen: how are you going to get positive circulation from a room that is one temp, just a question

Warm air rises Charlie.
Think of an attic and why it also needs vents at different levels…
Here is an excerpt from Peoples Gas calculation guide.

Gas appliances may be installed in a utility room and utilize indoor
air for combustion as long as the indoor air is provided to the
room through properly-sized grilles or a fully-louvered door.
The utility room shall be provided with two permanent openings
communicating directly with other space of sufficient volume so
that the combined volume of all such spaces meets the criteria foran unconfined space. The total input of all gas utilization
equipment installed in the combined spaces shall be used to
determine the required minimum volume. Each opening shall
have a minimum free area of not less that 1 in2 per 1000 Btu/hr of
the total input rating of all gas utilization equipment in the confined
space, but not less than 100 in2. One opening shall commence
within 12 inches of the top, and one opening shall commence
within 12 inches of the bottom of the utility room. The minimum
dimension of air openings shall be not less than 3 inches.
Hope that helps.

Since I have your attention Charlie I am looking at a large basement room with a Furnace HWH,gas dryer makeup air is from the area (not cat 4) and is there any other reason it is not allowed other than makeup air?
The room has glass block ( no opening) but is a very large space and furnace pretty much serves as a dividing wall from the rest of the basement.

One or two vents on the door?

If the vents are on the door, the answer from People’s Gas is “neither”.

Because the entire door should be louvered (According to People’s, our local AHJ).

If the combustion air vents are located on the wall, two are required, one high and one low.

Size of vents are determined by combined BTUs of all appliances in the room.

Local requirements may vary per AHJ.

Just messing with you thought you had went nighty nite. Your gas comapny is different than mine we only require one opening in the door of proper size due to the the same temp in the room as what is in the enclosed closet there is basically no circulation. Different story if the combustion air is taken from the attic which has a different temp than the enclosed closet

Go to bed now I am

You yankees have you own rules AHJ. down here if the basement is of proper size SQ FT Combustion air is allowed to be drawn from the interior basement. Are we talking full basement 1/2 basement or what size

The entire door does not need to be louvered if the two openings meet the requirements as stated.(bear in mind that a 12’"by 12’’ opening on a louvered door is not a complete opening).The slats are solid and take up space.
Hope that makes sense Tom.

Unusual setup that I will pull a pic off my video for you tomorrow.Get you’re sleep as I have all tomorrow to finish the report.

This gas water heater has been in place since 1998. Solid bi fold doors, no combustion air vents!!

Bob- I suggest you read page 14 of the construction guide. Call me if you have any questions.

Is there a point? and can you copy/paste it?

Here is more.

The confined space shall have two permanent openings. One opening
located within 12 inches of the ceiling, while the second opening is
located within 12 inches of the floor. (See Figure 5 on Page 14 and
Figure 6 on Page 15.) Each opening shall have a minimum free area
of one square inch per 1000 Btu per hour of the total input for all gas
appliances in the confined space, but not less than 100 square inches
of free area. In confined space situations, where there may be vertical
and/or horizontal space limitations,
it is permissible for the two
permanent openings to abut one another
.

Why would you think they want high and low.?
Think convection.
…and yes the ceiling area would be warmer as pilots give off heat even when the appliances are not running but a HTW or furnace defiantly give off heat and the higher the btus the more heat so the opening must be bigger.
Common sense.Hot air leaves the top opening and cooler makeup air enters the bottom .(they must be separated to stop tornado creation) ok made that part up:)

And, don’t forget to derate louvered door openings to actual net free area.