While all fume hoods operate on the same basic principles, all fume hoods are not created equal. The type of laboratory fume hoods you choose will depend upon their application.
There are two broad categories of fume hoods: general fume hoods, and specialty fume hoods.
General Fume Hoods
General fume hoods can be used in most applications, and are categorized into four types.
Conventional fume hoods vent a constant amount of air over a 24-hour period. The volume of air passed is controlled by the sash; the higher it is opened, the higher the volume of air and the lower the face velocity. Another type of conventional hood uses a bypass to keep air volume and face velocity constant, regardless of sash height. Conventional fume hoods vent conditioned lab air, and each hood requires about as much energy as a 2,500-square-foot home to operate!
Reduced flow fume hoods, like conventional fume hoods, also vent a constant volume of air. However, they vent air at volumes up to 50% lower than conventional fume hoods. This increases the safety of the user, and also reduces energy consumption.
Variable air volume hoods use a feedback system of controls to constantly adjust the volume of air being adjusted based on sash height. The end result is a constant face velocity across the front of the hood. There are several benefits to this type of hood, including decreased turbulence, increased user safety, and significantly decreased energy use.
Ductless fume hoods are used only in situations with minimal danger. These types of fume hoods filter laboratory air then recycle it.
Specialty Fume Hoods
Specialty fume hoods operate like general fume hoods, but are designed to manage applications beyond the scope of general fume hoods. Specialty fume hoods such as perchloric acid fume hoods, radioisotope fume hoods, distillation hoods, and ADA-compliant hoods each have unique design elements intended to increase the safety of the user and the environment. Some specialty fume hoods are made of materials designed to withstand certain chemicals, while others have specific fans, ducts, or washdown mechanisms.