18-28-927.5 Air supply.

   Ventilation air to the recirculating direct gas-fired industrial air heater shall be ducted directly from outdoors. Air to the recirculating direct gas-fired industrial air heater in excess of the minimum ventilation air specified on the heater's rating plate shall be taken from the building, ducted directly from outdoors, or a combination of both. Where outside air dampers or closing louvers are used, they shall be verified to be in the open position prior to main burner operation.

18-28-927.6 Atmospheric vents, gas reliefs, or bleeds.

   Recirculating direct gas-fired industrial air heaters with valve train components equipped with atmospheric, vents, gas reliefs, or bleeds shall have their vent lines, gas reliefs, or bleeds lead to a safe point outdoors. Means shall be employed on these lines to prevent water from entering and to prevent blockage from insects and foreign matter. An atmospheric vent line shall not be required to be provided on a valve train component equipped with a listed vent limiter.

18-28-927.7 Relief openings.

   The design of the installation shall include adequate provisions to permit the recirculating direct gas-fired industrial air heater to operate at its rated airflow without over-pressurizing the space served by the heater by taking into account the structure's designed infiltration rate, properly designed relief openings, an interlocked powered exhaust system, or a combination of these methods.

18-28-927.7.1

   The structure's designed infiltration rate and the size of relief opening(s) shall be determined by approved engineering methods.

18-28-927.7.2

   Louver or counterbalanced gravity relief openings shall be permitted.

   Where motorized dampers or closeable louvers are used, they shall be proved to be in their open position prior to main burner operation.

18-28-927.8 Purging.

   Inlet ducting, when used, shall be purged with at least four air changes prior to an ignition attempt.