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311.1 Source
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.
Exceptions:
  1. Systems serving single guest rooms or dwelling units shall not require a listed filter.
  2. Air filters used in listed appliances and in accordance with the manufacturer's instructions.
311.3 Prohibited Source
Outside or return air for a heating or cooling air system shall not be taken from the following locations:
  1. 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.
  2. Less than 10 feet (3048 mm) above the surface of an abutting public way, sidewalk, street, alley, or driveway.
  3. A hazardous or insanitary location, or a refrigeration machinery room as defined in this code.
  4. 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.
  5. A closet, bathroom, toilet room, or kitchen.
  6. 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 appliances, residential cooking appliances, direct-vent appliances, enclosed furnaces, and domestic-type clothes dryers installed within the room or space.
    2. This shall not apply to a gravity-type or listed vented wall heating or cooling air system.
    3. This shall not apply to a blower-type heating or cooling air system installed in accordance with the following requirements:
      1. 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.
      2. Not less than 75 percent of the supply air is discharged back into the same room or space.
      3. 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.
311.4 Return-Air Limitations
Return air from one dwelling unit shall not discharge into another dwelling unit through the heating or cooling air system.

Related Code Sections

311.0 General Regulations, Heating or Cooling Air System
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 ...
101.4.2 Scope and Administration, Mechanical
equipment, appliances, fixtures, fittings and appurtenances, including ventilating, heating, cooling, air-conditioning and refrigeration systems ...