How do Ducted Fume Hoods work?
A ducted fume hood creates a controlled inward airflow through the sash opening so contaminants generated inside are carried to the exhaust rather than into the room. Face velocity, typically 0.4–0.6 m/s at the sash, is produced by an exhaust fan located on the roof or in the duct. A baffle system at the rear distributes air across slots at the top, middle and bottom to avoid dead zones. A bypass airfoil keeps flow smooth as the sash moves. Variable air volume (VAV) hoods modulate exhaust as the sash opens or closes, saving energy while holding face velocity. The work surface, liner and sash are chemical resistant. Airflow monitors, alarms and lighting complete the hood, and the building make-up air system replaces exhausted air.
Which Ducted Fume Hoods variants are available?
- Constant Volume Bypass Fume Hood — A constant-volume bypass fume hood exhausts a fixed airflow and uses a bypass opening above the sash to keep face velocity within limits as the sash moves.
- Variable Air Volume (VAV) Fume Hood — A VAV fume hood adjusts exhaust volume as the sash is raised or lowered so face velocity stays constant.
- Walk-In Fume Hood — A walk-in fume hood is a floor-standing hood tall and deep enough to house large apparatus, reactors and drums.
- Benchtop Fume Hood — A benchtop fume hood is a compact ducted hood that sits on an existing bench or cabinet.
- Distillation Fume Hood — A distillation fume hood is a tall, deep ducted hood designed for distillation racks and reflux assemblies.
How do I choose the right variant?
Select the hood by the chemicals and process. Choose width, commonly 1200, 1500 or 1800 mm, to match equipment and operators, and check that depth and height suit tall apparatus. Decide between constant volume, bypass and VAV designs, taking the building's exhaust capacity and energy costs into account. Specify liner material: fibre-reinforced cement or epoxy for general use, stainless steel or polypropylene for acids. Consider sash type, vertical or combination, face velocity monitoring, service fittings and base cabinet for storage. Confirm whether perchloric acid or radioisotope work requires a specialised hood instead. Coordinate duct size, fan capacity and make-up air with the building engineer, and plan for containment testing.
Where are Ducted Fume Hoods used?
Ducted Fume Hoods are specified in chemistry laboratories, pharmaceutical research, materials testing, teaching laboratories and quality control.
Which standards and certifications apply?
Work with Ducted Fume Hoods is commonly governed by EN 14175-2 (fume cupboards, safety and performance), EN 14175-3 (type test methods), EN 14175-4 (on-site test methods), ASHRAE 110 (method of testing performance of laboratory fume hoods), GB/T 34269 and ISO 14644-1. Instrument certifications such as CE marking are confirmed per configuration and never assumed.
What are the key considerations before purchase?
Commission each hood with a face velocity survey and, where required, a containment test such as EN 14175-3 or ASHRAE 110. Place it away from doors, walkways and supply diffusers, since cross-drafts above 0.15 m/s degrade containment. Keep the sash at or below the marked working height, and avoid blocking baffles with equipment. Check airflow monitors, alarms and exhaust fans at least every 6–12 months, and clean the liner regularly. Plan make-up air so the room does not become negatively pressured. Train users and label the hood with its tested face velocity and date, and do not use it for storage of chemicals beyond what the work requires.
