FROM HUD 3280 CODE:
§ 3280.710 Venting, ventilation and combustion air.
(a) The venting as required by §3280.707(b) shall be accomplished by one or more of the methods given in (a)(1) and (2) of this section:
(1) An integral vent system listed or certified as part of=2 0the appliance.
(2) A venting system consisting entirely of listed components, including roof jack, installed in accordance with the terms of the appliance listing and the appliance manufacturer's instructions.
(b) Venting and combustion air systems shall be installed in accordance with the following:
(1) Components shall be securely assembled and properly aligned at the factory in accordance with the appliance manufacturer's instructions except vertical or horizontal sections of a fuel fired heating appliance venting system that extend beyond the roof line or outside the wall line may be installed at the site. Sectional venting systems shall be listed for such applications and installed in accordance with the terms of their listings and manufacturers' instructions. In cases where sections of the venting system are removed for transportation, a label shall be permanently attached to the appliance indicating the following:
Sections of the venting system have not been20installed. Warning-do not operate the appliance until all sections have been assembled and installed in accordance with the manufacturer's instructions.
(2) Draft hood connectors shall be firmly attached to draft hood outlets or flue collars by sheet metal screws or by equivalent effective mechanical fasteners.
(3) Every joint of a vent, vent connector, exhaust duct and combustion air intake shall be secure and in alignment.
(c) Venting systems shall not terminate underneath a manufactured home.
(d) Venting system terminations shall be not less than three feet from any motor-driven air intake discharging into habitable areas.
(e) The area in which cooking appliances are located shall be ventilated by a metal duct which may be single wall, not less than 12.5 square inches in cross-sectional area (minimum dimensio n shall be two inches) located above the appliance(s) and terminating outside the manufactured home, or by listed mechanical ventilating equipment discharging outside the home, that is installed in accordance with the terms of listing and the manufacturer's instructions. Gravity or mechanical ventilation shall be installed within a horizontal distance of not more than ten feet from the vertical front of the appliance(s).
(f) Mechanical ventilation which exhausts directly to the outside atmosphere from the living space of a home shall be equipped with an automatic or manual damper. Operating controls shall be provided such that mechanical ventilation can be separately operated without directly energizing other energy consuming devices.
[49 FR 32012, Aug. 9, 1984, as amended at 58 FR 55018, Oct. 25, 1993]