Separate Outdoor Air Intakes
from Air Pollutant Sources

Outdoor air intakes located near pollutant sources are a common cause of indoor air quality problems, often affecting occupant health. Intakes and operable windows should be located as far as possible from potential pollutant releases.

Generic recommendations for “stretched string” separation distances between pollutant sources and outdoor air intakes or the property line are summarized in the accompanying table. (“Stretched string” distance is measured from the closest point of the pollutant source to the closest point of the outdoor air intake, window or door opening, or the property line, along a path as if a string were stretched between them.)

Minimize the risk of drawing contaminated air from building vents and exhausts into air intakes:

• Extend combustion equipment vent outlets on roofs above the turbulent air boundary.
• Exhausts with significant contaminants, toxic fumes or gases should be directed vertically to ensure their plumes are carried away from the roof and turbulent wake downwind of the building.
• Avoid locating intakes in semi-enclosed areas with exhausts, vents, cooling towers or evaporative coolers.

Be careful to avoid locating outdoor air intakes where they may capture air from automobiles and trucks, especially where vehicles may be idling while stopped, such as loading bays, passenger drop-off zones and parking areas, or near roads with heavy traffic.

Cautions

• Separation distance recommendations are generic. Review site conditions carefully, and perform a separation analysis per ASHRAE Fundamentals 1997, Chapter 15 where any uncertainty exists.
• Plumbers often locate plumbing vents without noting air intake locations.

Recommended Separation Distances of Ventilation Outside- Air Intakes & Pollutant Sources
Pollution Source	Distance from Outdoor Air Intake (ft.)	Distance from Property line (ft.)	Notes
Property line	3	-
Garage entry, loading areas, or drive-in queue	25	-	Note 1
Driveway or street	10	-	Note 1
Limited access highway	25	-	Note 1
Mantles or ledges (sloped less than 1:1 and more than 6 inches wide)	3	-
Landscaped grade	6 (8)	-	Note 2
Roof or grade	1.5	-
Air exhausted or vented from spaces without unusual contaminants: e.g. offices, conference rooms, classrooms, lobbies, retails paces, coffee stations, storage & air handling or elevator machine equipment rooms, individual dwelling units including hotel rooms, and electrical.telephone closets.	5	0	Note 1, Note 3
Air exhausted or vented from spaces that may have mild contaminant intensity: eg: copy or printer rooms, dining areas and break rooms, kitchenettes or dining areas with ovens or other cooking of floor dispensing capability such as steam tables, cafeterias, laundry rooms, locker rooms, residential kitchens, limited access toilet rooms, and residential bathrooms.	9	5	Note 3, Note 4
Air exhausted or vented from locations with significant contaminant intensity: Public toilet rooms, health care facility bathrooms, janitor's closets, commercial kitchens, laboratories general exhaust, dry-cleaning establishments general exhaust, indoor swimming pools, diazo printing rooms, etc.	13	10	Note 3, Note 4
Gravity and plumbing vents	19	10
Air drawn or vented from locations with noxious or toxic fumes or gases: Natural gas and propane appliance vents, paint spray booths, garages, tunnels, kitchen hood exhaust, laboratory filtered fume hood exhaust, chemical storage rooms, refrigerating machinery rooms and soiled laundry storage, etc.	18	10	Note 5
Effluent or exhaust air having a high concentration of dangerous particles, bio-aerosols, or gases: eg: fuel-burning appliance vents (other than natural gas and propane), uncleaned fume hood exhaust, evaporative condenser and cooling tower outlets.	26	15	Note 6
Note 1: Per UMC 317.6 minimum separation of ventilation outside air for heating from exhaust outlets, appliance vents, plumbing vents is 10 feet unless outlet is 3 feet above outside air inlet; and for horizontal intakes abutting sidewalk, streets, alleys or driveways. Larger distances may be necessary if intake is above likely location of vehicles. Note 2: Soil, lawn or plants within 1.5 ft horizontally from intake. UMC 405.2 requires 8 feet above grade for health facilities. Note 3: Assumes 500 fpm exhaust velocity directed away from outdoor air intake. Note 4: 0 ft separation from property line if property line abuts a street or public way and outlet is at least 10 ft above grade. Note 5: Assumes 500 fpm vent exit velocity directed vertically up. Note 6: Assumes 750 fpm exhaust velocity directed vertically up, and that exhaust is located above or at same level as intake. General Note: Separation distances do not apply to explosive or flammable vapors, fumes or dust
Source: Proposed ASHRAE Standard 62R (1997)

 

Linked Practices EN3 - daylighting: roof monitors HS2 - isolate indoor pollutants LA2 - landscape & ventilation Further Information

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