How do Ductless Fume Hoods work?
A ductless fume hood uses a fan to pull room air through the sash opening at 0.4–0.5 m/s across the work area, then through one or more filter stages before discharge back into the room. A prefilter removes dust, and activated carbon beds adsorb organic vapours through physical adsorption. Chemically impregnated carbon or specialist media can capture acids, ammonia or formaldehyde. A HEPA stage can be added for particles. Sensors or timers indicate filter saturation, and airflow monitors ensure correct face velocity. Because filters have finite capacity, the hood is limited to known chemicals in limited quantities, and filter selection must match the vapour. The body is typically polypropylene or epoxy-coated steel, with lighting and a control panel.
Which Ductless Fume Hoods variants are available?
- Activated Carbon Ductless Fume Hood — An activated carbon ductless hood filters organic vapours through carbon adsorption beds before recirculating air into the room.
- HEPA and Carbon Ductless Fume Hood — A combined HEPA and carbon ductless hood filters both particulates and organic vapours in a two-stage design.
- Acid Gas Ductless Fume Hood — An acid gas ductless hood uses chemically impregnated carbon or alkaline media to neutralize acid vapours such as HCl, HF and SO2.
- Portable Ductless Fume Extractor Hood — A portable ductless fume extractor hood is a small, movable unit with a capture hood and filter set for soldering, adhesives or light chemical tasks.
- Ammonia and Amine Ductless Fume Hood — An ammonia and amine ductless hood uses acid-impregnated carbon media to chemisorb alkaline vapours such as ammonia, trimethylamine and volatile amines.
How do I choose the right variant?
Select by the chemicals used. Every application needs a chemical compatibility assessment from the supplier to match filter media, and the assessment should include quantities, frequency and breakthrough behaviour. Choose an activated carbon filter for organic solvents, impregnated carbon for acids or amines, and HEPA for particulates. Consider filter monitoring, such as gas sensors that signal breakthrough, rather than timers alone. Choose width, typically 600–1500 mm, noise level, and whether a base cabinet for storage is required. Ductless hoods are not suitable for unknown, high-volume or highly toxic chemicals, or for heated perchloric acid. Confirm local regulations on recirculating air, since some jurisdictions restrict their use.
Where are Ductless Fume Hoods used?
Ductless Fume Hoods are specified in teaching laboratories, quality control, pharmacies, electronics repair and small-scale chemistry.
Which standards and certifications apply?
Work with Ductless Fume Hoods is commonly governed by ASHRAE 110 (testing performance of laboratory fume hoods), AFNOR NF X 15-211 (ductless fume cupboards), ISO 14644-1, EN 14175-1 (fume cupboards, vocabulary), GB/T 34269 and IEC 61010-1. Instrument certifications such as CE marking are confirmed per configuration and never assumed.
What are the key considerations before purchase?
Establish a chemical register before purchase and have the supplier confirm filter compatibility in writing. Change filters at the recommended interval or sooner if gas sensors or odour indicate breakthrough, because carbon saturation is sudden at the end of life. Test airflow and filter seals on installation and at least every 6–12 months, keeping records for audit. Place the hood away from doors and air currents, and with clearance to allow filter replacement. Dispose of used filters as hazardous waste. Train users to restrict quantities, keep sashes low and never use the hood for chemicals outside the compatibility list.
