Tri-Stack Exhaust Fan Centrifugal Exhaust Fan

Tri-Stack® Systems Provide Significant Performance, Reliability, and Cost Advantages Over Conventional Centrifugal Exhaust Fans

Strobic Air Tri-Stack®


  • 7 year motor warranty, an industry first
  • No need for unsightly guy wires
  • Long bearing life L 10 up to 364,000 hours 6
  • Belts and pulleys not needed
  • Maximum Entrainment provided
  • Flexible connection and spring isolation not needed
  • Stack and nozzle loss already built into fan curves
  • Lower stack height provides lower roof profile and center of gravity


Typical Centrifugal

  • Standard motor warranty offered
  • Additional stack height requires use of guy wires
  • With a bearing life L 10 = 40,000 hrs (pillowblock), and L 10 = 40,000 hrs (motor bearings), the belt-driven centrifugal has a 5x greater chance of motor or bearing failure, requiring change-out
  • Losses through belts and pulleys require more energy
  • Minimal or no entrainment provided
  • Flexible connection required on the inlet and outlet of fan are prone to failure
  • In order to match the outlet velocity of the Tri-Stack®, a nozzle is needed, which requires an additional 1.12” of static pressure and more energy
  • Larger footprint requiring more valuable space on the roof

Strobic Air has been refining the technology of mixed flow fans for more than two decades, and has pioneered many aerodynamic concepts associated with mixed flow fan technology. Mixed flow fans–originally developed for low pressure, high flow applications–provide optimum performance in virtually all configurations of low pressure and high flow, and high pressure and low flow. They offer substantial advantages over centrifugal-type fans such as higher efficiency performance for lower horsepower requirements for comparable pressures and flows, as well as energy efficient operation. The constant acceleration ratio of mixed flow fan blades permits both the leading and trailing edges to perform equal work, maximizing efficiency and providing a stable performance curve without stall or unstall sections.

Because Tri-Stack® fume exhaust systems require little or no maintenance, health and safety considerations of maintenance people (on the roof) are eliminated, while freeing them for more productive work. In addition, the need for rooftop penthouses to protect maintenance workers is also eliminated, reducing costs and weight on the roof structure.

On a direct operating cost basis, use of Tri-Stack® mixed flow fan technology reduces energy consumption as indicated in the chart. When combined with accessory heat recovery systems, Tri-Stack® systems dramatically lower overall energy costs for building climate control.

 Tri-Stack Model
Centrifugal Fan
81" SWI-BC
Housing Diameter 54” 81”
Flow Rate (CFM) 33253 33253
Inlet SP (In. W.G.) 3.00 3.00
Outlet Velocity (FPM) 6239 6239
Inlet Duct Size 57"SQ 42" DIA
Inlet Velocity (FPM) 1474 3456
Changes in Static Pressure 1
90 Deg. Inlet Elbow NOT REQ'D 2 0.60 in.
Inlet Flex Connection NOT REQ'D 2 0.20 in.
System Effect NOT REQ'D 2 0.20 in.
45 Deg. Outlet NOT REQ'D 2 0.21 in.
Stack Loss NOT REQ'D 3 0.03 in.
Nozzle Loss NOT REQ'D 3 1.12 in.
New Static Pressure 3.00 5.36 in.
Required Horsepower
Fan HP 33.89 46.75 5
Belt % Loss NO LOSS 4 5%
Belt Loss NO LOSS 4 2.34
Motor HP 33.89 49.09
Motor Required 40HP 50HP
Cost Analysis
Annual Energy Cost @ $0.12/KWH 7 $33,213.33 $48,862.58
Maintenance Required/ Month (Belt Maint. Per ANSI Z9.5) 0 4
Annual Maint. Cost @ $65/MH $0.00 $3,120.00
Annual Operating Cost/Fan $33,213.33 $51,982.58
Annual Savings Per Fan $18,769.25 ----
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Tri-Stack® Fan Selection Program