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Providing a source of outside air compliant with NFPA regulations and recommendations

Fresh air stack with dual unit adapterAs a recommended and often required addition to a purge and pressurization unit (PPU) or InPac® unit, the stack package provide an easy means of providing fresh air to areas needing a source of non-hazardous air. Two basic designs are available. The standard stack package, comprised of spiral wound galvanized steel, is designed to tolerate wind gusts and steady winds up to 90 MPH, and our high wind design is capable of withstanding winds up to 120 MPH.

  • Standard stacks and rain caps are composed of 16 gauge galvanized steel.
  • Rain cap included which is manufactured from the same material as the stacks themselves.
  • Upgrade to spiral wound 304 or 316 stainless steel is available if further corrosion protection is needed.
  • Free standing stacks available in both galvanized and stainless steel as well.
  • Recommended as a source of fresh air in hazardous (classified) areas to meet ASHRAE 62.1 (15 cfm/person).

Why would I need a stack?

NFPA 496 (7.2) dictates that “protective gas” shall be air that is free of contaminants and contains only trace amounts of hazardous gas or vapor. It is further agreed that fresh air can be pulled as a protective air from a height of 25' above ground level because the prevalent hazardous gases are heavier than air, and therefore sink.

  • Rain caps are designed to fit directly onto the corresponding stack diameter without use of an extra flange.
  • Caps are also engineered to deter the nesting of birds.
  • Rain caps include a grate that allows for excellent air flow while protecting against the elements and large debris.

Available Options

Because roof top units are already several feet above the ground, they require the shortest stacks.

  • Available in 12", 16", 18", and 24" sizes, with rain caps sized to meet the stacks with which they are shipped.
  • Free standing stacks are mounted via a T-adapter and a base that is bolted to the ground.
  • Multiple units have the option of sharing a stack with a single plenum routing fresh air to both units simultaneously.
  • All units have the option of directly mounting the stack to the unit via a flange on the top.


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