Thread: Cold air return

Did an inspection today, one story Ranch on a crawl space.
My question, the furnace is using crawl for the cold air return. Are there any issues with this.
There are no vent to the outside.
Any help would be great.

Bill

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do you mean they are using air from the crawl area for the return air and not recirculatiing air from the interior of the home. If so that's NOT GOOD!! Radon, Mold, etc being drawn into the home among other issues.

Wrong.

From the IRC. (underlining is mine)
- SECTION M1602

- - RETURN AIR

- - - M1602.1 Return air.

Return air shall be taken from inside the dwelling. Dilution of return air with outdoor air shall be permitted.

From the UMC 2000 aka CMC:
906.0 - Return and Outside Air
906.1 Source. A warm air furnace shall be provided with return air, outside air, or both. Heating systems regulated by this code and designed to replace required ventilation shall be arranged to discharge into the conditioned space not less than the amount of outside air specified in the Building Code.
906.2 Separation. Except as permitted by the exceptions to Section 906.6, there shall be a positive separation between combustion air and outside or return air for blower type heating systems. The combustion chamber opening shall be separated from a fan plenum by an airtight separation without openings therein, except through an air lock at least 16 square feet (1.49 m2) in area, equipped with tight fitting doors arranged to close automatically. A fan plenum access not exceeding twenty-four (24) by thirty (30) inches (610 mm x 762 mm) may be equipped with a tight fitting panel or door.
906.3 Area Requirements. The minimum unobstructed total area of the outside or return air ducts or openings to a gravity type warm air furnace shall be not less than seven (7) square inches (4516 mm2) per 1000 Btu/h (293 W) approved output rating or as indicated by the conditions of listing of the furnace.
The minimum unobstructed total area of the outside or return air ducts or openings to a blower type warm air furnace shall be not less than two (2) square inches (1290 mm2) per 1000 Btu/h (293 W) approved output rating or bonnet capacity of the furnace.
The total area of the outside or return air ducts or openings need not be larger than the minimum indicated by the conditions of listing of the furnace.
The minimum unobstructed total area of the outside or return air ducts or openings to a heat pump shall be not less than six (6) square inches (3871 mm2) per 1000 Btu/h (293 W) nominal output rating or as indicated by the conditions of listing of the heat pump.
Exceptions: Complete duct systems for blower-type warm-air furnaces or heat pumps that are sized in accordance with Chapter 16, Part II Referenced Standards or by other approved methods.
906.4 Dampers. Volume dampers shall not be placed in the air inlet to a furnace in a manner which will reduce the required air to the furnace.
906.5 Ducts for Blower Type Warm Air Furnace. Except as provided in Section 906.6, air for every fuel burning blower type warm air furnace shall be conducted into the blower housing from outside the furnace space by continuous airtight ducts.
906.6 Prohibited Sources. Outside or return air for a heating system shall not be taken from the following locations:
906.6.1 Closer than ten (10) feet (3048 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.
906.6.2 Where it will pick up objectionable odors, fumes or flammable vapors; or where it is less than ten (10) feet (3048 mm) above the surface of any abutting public way or driveway; or where it is in a horizontal position in a sidewalk, street, alley or driveway.
906.6.3 A hazardous or insanitary location or a refrigeration machinery room as defined in this code.
906.6.4 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. This permanent opening, when used to provide return air to a warm air furnace, shall be of sufficient area to comply with Section 906.3.
Exception: Such opening when used for a warm air furnace in a dwelling unit may be reduced to no less than 50 percent of the required area, provided the balance of the required return air is taken from a room or hall having at least three doors leading to other rooms served by the furnace.
906.6.5 From a room or space having any fuel burning appliances therein.
Exception: This shall not apply to:
1. Fireplaces, fireplace appliances, residential cooking appliances, direct vent appliances, enclosed furnaces and domestic type clothes dryers installed within the room or space.
2. A gravity type or listed vented wall furnace.
3. A blower type system complying with the following requirements:
Where the return air is taken from a room or space having a volume exceeding one (1) cubic foot (0.028 m3) for each ten (10) Btu/h (2.93 W) fuel input rate of all fuel burning appliances therein.
At least 75 percent of the supply air is discharged back into the same room or space.
Return air inlet shall not be located within ten (10) feet (3048 mm) of any appliance firebox or draft diverter in the same enclosed room or confined space.
906.6.6 A closet, bathroom, toilet room or kitchen.
906.7 Screen. Required outside air inlets shall be covered with screen having 1/4 inch (6.4 mm) openings.
Exception: An outside air inlet serving a nonresidential portion of a building may be covered with a screen having openings larger than 1/4 inch (6.4 mm), but in no case larger than one (1) inch (25.4 mm).
906.8 Return Air Limitation. Return air from one dwelling unit shall not be discharged into another dwelling unit through the heating system.

Thanks all,
It looks like this is acceptable.

1.There are no vents to the outside so no out side air.

2. No romex wire in crawl

3. There are floor vents in every room open to the crawl.

Again thanks

Bill

Bill what area are you in? Your profile is not filled out.

Even if the crawl is sealed and it is being used as the return for the HVAC, this is not good. It is a kin to the old slab ducts. I can see all types of problems down the road with this.

Regardless of whether or not this type of configuration is allowed, it does not make good sense. Pulling air from the crawl will depressurize (or is the term I want pressurize)the space and draw stagnant air from an uninhabitable space into the house, and possibly create moisture and radon issues where they may not have existed otherwise.

Nick,
I agree it's not the best.
I think i'll just report some of the conserns, I'm referring to a HVAC tech for other reasons.

Thanks

Bill

Scott,

Thanks profile updated.

Bill