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Exhaust air: Air removed from a space to the outside atmosphere and not to be reused.

Exhaust system: An assembly of connected ducts, plenums, fittings, registers, grilles, dampers, blowers, fans and hoods through which air is conducted from the space or spaces and exhausted to the outside atmosphere.

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Return air system: An assembly of connected ducts, plenums, fittings, dampers, blowers, fans, registers and grilles through which air from the space or spaces to be heated or cooled is conducted back to the supply unit (see also "Supply air system").

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Supply air system: An assembly of connected ducts, plenums, fittings, dampers, blowers, fans, registers and grilles through which air, heated or cooled, is conducted from the supply unit to the space or spaces to be heated or cooled (see also "Return air system").

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M-303.4 Stud and joist spaces - (Delete paragraph in its entirety as written - substitute as follows)

M-303.4 Stud cavity and joist space plenums: Stud wall cavities and the spaces between solid floor joists to be utilized as air plenums shall comply with the following conditions:

1. Such cavities or spaces shall not be utilized as a plenum for supply air.

2. Such cavities or spaces shall not be part of a required fireresistance rated assembly.

3. Stud wall cavities shall not convey air from more than one floor level.

4. Stud wall cavities and joist space plenums shall comply with the floor penetration protection requirements of the building code.

5. Stud wall cavities and joist space plenums shall be isolated from adjacent concealed spaces by approved fireblocking as required in the building code.

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