Return air question

[Marc M]

I was reading this section and wanted to get some of your opinions on this section specifically the last exception. Am I correct to interpret this as saying that those areas listed "are" allowed?
Or is it saying that these areas are not allowed simply by exclusion?
Thanks..

2010 CMC 311.3 Prohibited Source. Outside or return air for a heating

or cooling air system shall not be taken from the following
locations:
(1) Closer than ten (10) feet (3,048 mm) from an appliance
vent outlet, a vent opening of a plumbing drainage system,
or the discharge outlet of an exhaust fan, unless the outlet
is three (3) feet (914 mm) above the outside-air inlet.
(2) Where it is less than ten (10) feet above the surface of
any abutting public way, driveway, sidewalk, street, alley
or driveway.
(3) A hazardous or insanitary location or a refrigeration
machinery room as defined in this code.
(4) From an area, the volume of which is less than 25 percent
of the entire volume served by such system, unless there
is a permanent opening to an area the volume of which is
equal to 25 percent of the entire volume served.
Exception: Such openings when used for a heating or

cooling air system in a dwelling unit shall be permitted

to be reduced to not less than 50 percent of the required
area, provided the balance of the required return air is
taken from a room or hall having not less than three (3)

doors leading to other rooms served by the furnace.
(5) A closet, bathroom, toilet room, or kitchen.
(6) From rooms or spaces containing a fuel-burning appliance
therein.Where such room or space serves as source
of return air.
Exceptions:
(1) This shall not apply to fireplaces, fireplace appliance,
residential cooking appliance, direct vent
appliance, enclosed furnaces, and domestic-type
clothes dryers installed within the room or space.

[Rick Cantrell]

It's easy to follow once you know who's on first.

[Jim Luttrall]

I was reading this section and wanted to get some of your opinions on this section specifically the last exception. Am I correct to interpret this as saying that those areas listed "are" allowed?
Or is it saying that these areas are not allowed simply by exclusion?
Thanks..

2010 CMC 311.3 Prohibited Source. Outside or return air for a heating

or cooling air system shall not be taken from the following
locations:
(1) Closer than ten (10) feet (3,048 mm) from an appliance
vent outlet, a vent opening of a plumbing drainage system,
or the discharge outlet of an exhaust fan, unless the outlet
is three (3) feet (914 mm) above the outside-air inlet.
(2) Where it is less than ten (10) feet above the surface of
any abutting public way, driveway, sidewalk, street, alley
or driveway.
(3) A hazardous or insanitary location or a refrigeration
machinery room as defined in this code.
(4) From an area, the volume of which is less than 25 percent
of the entire volume served by such system, unless there
is a permanent opening to an area the volume of which is
equal to 25 percent of the entire volume served.
Exception: Such openings when used for a heating or

cooling air system in a dwelling unit shall be permitted

to be reduced to not less than 50 percent of the required
area, provided the balance of the required return air is
taken from a room or hall having not less than three (3)

doors leading to other rooms served by the furnace.
(5) A closet, bathroom, toilet room, or kitchen.
(6) From rooms or spaces containing a fuel-burning appliance
therein.Where such room or space serves as source
of return air.
Exceptions:
(1) This shall not apply to fireplaces, fireplace appliance,
residential cooking appliance, direct vent
appliance, enclosed furnaces, and domestic-type
clothes dryers installed within the room or space.
Kind of hard to follow the flow due to changes in fonts in the quote, but the way I read this and the way it makes the most sense is that the RED TYPE exceptions mean that they are allowed ONLY as related to item (6) but all the other prohibitions above still apply.
i.e. - you CAN have a cooking appliance in a room that also has a return air vent but the prohibitions of item (4) above would still apply. Which means 75% of the return air of the system would have to come from another room.

[Marc M]

Yea sorry about the fonts. I tried to fix this but for whatever reason couldn't. Anyhow, thanks for the info Jim, much appreciated.



Kind of hard to follow the flow due to changes in fonts in the quote, but the way I read this and the way it makes the most sense is that the RED TYPE exceptions mean that they are allowed ONLY as related to item (6) but all the other prohibitions above still apply.
i.e. - you CAN have a cooking appliance in a room that also has a return air vent but the prohibitions of item (4) above would still apply. Which means 75% of the return air of the system would have to come from another room.