Industrial gas fired air handling fan units AHU and heated air curtains. Sales of roof and wall air make up fan ventilators, hooded fans, upblast and downblast roof power fans.
Industrial fans and blowers

Practically all air removed from a building is replaced by outside air at the same rate. Outside air will enter by any means available, when the inside air pressure is less than outside air pressure. This happens when exhaust exceeds supply systems capacity to replenish the building envelope with air. Possible consequences of this negative pressure differential are degraded exhaust system performance, loss of environmental control, adverse safety and performance effects on appliances which combust fuel and processes which vent gaseous products via natural draft, increased building structural loads, and excessive forces on exterior doors. Unfortunately, these problems occur where an inadequate amount of replacement or make-up air has been provided. A good make-up air system will alleviate all of these ills by providing the correct amount of replacement air. It may also reduce plant overhead by lowering heating, cooling, and ventilating costs.

In many areas, air must be conditioned before entering a facility. This necessitates that the make-up air system have heating and often air cooling and filtering abilities. A so called make-up air unit is required. Typically a make-up air system includes an air mover section, usually a propeller or centrifugal type fan, an air tempering section containing heating and where necessary cooling and filtering equipment, and a control system.

Fan selection and power requirements are generally determined by the application. When only general ventilation is required (fan pressure requirements are low), a propeller type fan can be utilized. To supply make up air through a duct system with a resistance of 0.5 in w.g. or more, a centrifugal fan should be considered. In either system, diffusers may be used to direct the discharge air velocity.

In situations where the inside air quality is acceptable, often a portion of the inside air may be drawn back through the make-up air unit where it is recirculated back into the building. Advantages of using Hartzell Recirculating Make-Up Air units are lowered heating costs, better indoor air mixing (reduced air stratification), as well as constant building pressurization.