Double stage axial fans is a two-stage axial flow fan, which develops double the pressure rise compared to that of a conventional single stage fan. The fan has two impellers mounted on a common shaft with a guide vane arrangement between the two impellers. The fans operating point is quickly adjusted to the system load demand by varying the pitch of the hydraulically adjustable impeller blades. These fans are applied where high static pressure is required or where the static pressure per stage should be reduced so that a smaller hub diameter can be used. There are two ways to design these fans: (1) with two fan wheels rotating in the same direction and with guide vanes placed between the two stages or (2) with two counter-rotating fan wheels and no guide vanes at all. By either method, the two-stage unit will approximately double the static pressure.

Direct-fired gas air make-up units are air supply system in a self-contained package with fan, burner and controls. It is used in connection of gas line and power source. It features heavy-duty forward curved or backward inclined DWDI centrifugal blower and peaked roof to eliminate standing water. It contains 14-gauge galvanized steel housing and remote operating station.

The direct fired heater refers to heating equipment that burns gas directly in the fresh air stream resulting in the most efficient method of heat transfer. It generates the lowest cost per BTU of heating when compared to indirect-fired and electric strip heaters. These direct-fired heaters are well suited and widely accepted for applications such as commercial kitchens, service garages, transit facilities, factories, warehouses and paint-booths. The direct-fired heater incorporates intelligent flame monitoring equipment. This equipment ensures that the airflow through the burner and gas flow to the burner are optimized to produce the most efficient and clean combustion process.