Auxiliary Air Fume Hoods

Auxiliary air fume hoods are a type of laboratory fume hood designed to reduce the consumption of conditioned room air by introducing unconditioned or partially conditioned outside air (makeup air) directly at the hood’s face. This air supplements the exhaust, minimizing the amount of tempered (heated or cooled) room air drawn out, which can lead to energy savings in labs with limited air supply or high HVAC costs. They are typically a variation of bypass fume hoods, featuring an auxiliary air plenum above the sash to deliver this external air.

 

---

Key Features:

• Energy Efficiency: By using outside air, they reduce the energy needed to condition room air, potentially lowering HVAC costs. For example, with the sash half-open at a face velocity of 100 feet per minute, exhaust air volume can equal auxiliary air supply, requiring no room air.

• Design: Incorporates a bypass mechanism to maintain relatively constant air volume and limit face velocity increases as the sash closes, reducing turbulence and air spillage.

• Sizes: Commonly available in 4’, 5’, and 6’ widths, with UL/CSA-listed electrical components, requiring separate supply air ducting and remote blowers.

---

Key Recommendations

• Ensure auxiliary air is pre‑conditioned (cooled/heated and filtered) before entering the hood.
• Maintain strict balance of auxiliary air, exhaust air, and room air—never overpressurize the hood face.
• Conduct proper airflow validation and testing, including alarms and face-flow monitors.
• Consider simpler alternatives like VAV or low-flow hoods for longer-term flexibility and easier relocation.