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311.0 Heating or Cooling Air System
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A heating or cooling air system shall be provided with return air, outside air, or both. A heating or cooling air system regulated by this code and designed to replace required ventilation shall be arranged to discharge into a conditioned space not less than the amount of outside air specified in Chapter 4.
311.2 Air Filters
Air filters shall be installed in a heating, cooling, or makeup air system. Media-type air filters shall comply with UL 900. Electrostatic and high efficiency particulate filters shall comply with Section 936.0.
311.3 Prohibited Source
Outside or return air for a heating or cooling air system shall not be taken from the following locations:
- Less than 10 feet (3048 mm) in distance 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 3 feet (914 mm) above the outside-air inlet.
- Less than 10 feet (3048 mm) above the surface of an abutting public way, sidewalk, street, alley, or driveway.
- A hazardous or insanitary location, or a refrigeration machinery room as defined in this code.
- 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 where 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 doors leading to other rooms served by the furnace.
- A closet, bathroom, toilet room, or kitchen.
- Rooms or spaces containing a fuel-burning appliance therein. Where such room or space serves as source of return-air.
- This shall not apply to fireplaces, fireplace appliances, residential cooking appliances, direct-vent appliances, enclosed furnaces, and domestic-type clothes dryers installed within the room or space.
- This shall not apply to a gravity-type or listed vented wall heating or cooling air system.
- This shall not apply to a blower-type heating or cooling air system installed in accordance with the following requirements:
- Where the return air is taken from a room or space having a volume exceeding 1 cubic foot (0.03 m3) for each 10 Btu/h (0.003 kW) fuel input rating of fuel-burning appliances therein.
- Not less than 75 percent of the supply air is discharged back into the same room or space.
- Return-air inlets shall not be located within 10 feet (3048 mm) from an appliance firebox or draft diverter in the same enclosed room or confined space.
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