How to Choose the Lab Fume Hood?

Choosing the fitting fume hood is crucial to ensuring safety from dangerous chemicals and vapors in your lab. However, researching and purchasing the right lab hood can seem overwhelming. We are here to help. Below are important questions and considerations to help you choose the fitting fume hood for your lab. Give us a call to speak with one of our product specialists, or feel free to send an email or reach out on live chat. Terra manufactures and stocks fume hoods in Fullerton, CA, and distributes industry-leading models by Labconco.

1. Fume Hood Application: What work are you doing inside your fume hood?
This worksheet will help you fill in the questions. But, first, review your experiment methods and material list.

Indicate which chemicals, or solvents, you will use and the concentration of each chemical. Note if you will use the chemicals separately, simultaneously, or combined in a mixture. Specific chemicals, such as Hydrofluoric Acid and Perchloric Acid, may require exceptional filtration.
Determine the evaporation rate of the chemicals. Evaporation rates are paramount because chemical solvents evaporate at different rates and, if not accounted for, can overwhelm the fume hood by disappearing at speed too fast for the fume hood to ventilate. This will lead to fugitive emissions that could migrate into the lab. So instead, the fume hood will ventilate the appropriate chemical solvents.
The evaporation rate is a function of temperature. Therefore, determine the average temperature for the chemicals used and whether the substances are being boiled or heated. It is also beneficial to note any exothermic reactions or open flames.
If you do not know the evaporation rate, you can list the type of containers used, such as a 100 ml beaker. Additionally, note the amount of exposed surface area for the container and the amount of time the container will be open.
2. Required Work Area: What size lab hood do you need?
Below are a few key factors to consider when determining the size of your fume hood.

Equipment: Will you have equipment inside your laboratory fume hood? If so, how large is the equipment? For example, a benchtop fume hood houses smaller items like scales or glass beakers. On the other hand, a walk-in fume hood might be more appropriate if your application involves extra-large equipment, such as drum containers.
Number of People: How many people will work simultaneously under the fume hood?
Depth: Take into account buffer space. Perform your work at least 6 inches behind the sash (the front-mounted safety shield) to ensure a safety buffer zone is maintained.
Height: Ensure your lab has ample height clearance for a more oversized bench top or floor-mounted fume hood.
3. Ducted vs. Ductless Fume Hood: How will fumes be filtered and exhausted?
A ducted fume hood connects to a remote blower or the facility HVAC system to safely remove toxic or dangerous chemicals from the work area. Depending on the type of chemicals being exhausted, air may require filtration by a facility fume scrubber before terminal exhaust from the building. Remote blowers are available in different materials to support specific applications. For example, choose fiberglass for moderate to highly corrosive vapors, epoxy-coated steel for low to moderately caustic fumes, PVC (Polyvinyl chloride), and Polypropylene for harsh acids.
A ductless fume hood contains an integral blower, carbon filters to capture chemical vapors, and, if required, HEPA/ULPA particle filters to allow exhaust air recirculation. The integrated blowers in these hoods recycle air into the room instead of the outside environment. This type of lab hood is ideal for spaces bereft of HVAC access. Don’t use this chemical fume hood for work with biohazards or radiological.
4. CAV vs. VAV: Which ventilation system should you use for a ducted fume hood?
A ducted fume hood has two options for ventilation control, constant air volume (CAV) and variable air volume (VAV). To choose between CAV and VAV, you must consider operating duration and budget.

Constant air volume (CAV) fume hoods provide continuous airflow regardless of sash position. The blower will pull a constant airflow anyway if the sash is lowered. Lab hoods with CAV systems are ideal for light-duty performance; however, generally, they are less energy-efficient than fume hoods with VAV.

Variable air volume (VAV) generally provides higher energy efficiency. The remote blower adjusts airflow based on the sash height. Airflow decreases when the sash is lowered, and the belt is raised—the decrease in overall airflow results in higher energy efficiency and lower operating costs.

5. What are the installation and operating costs of a fume hood?
Install costs: A ducted fume hood generally has higher install costs. This is because ducted fume hoods require HVAC systems (e.g., cooling/heating systems, exhaust fans, and ductwork). On the other hand, a ductless fume hood recirculates air back into the lab and therefore does not require an HVAC system to exhaust fumes.
Operating costs:
Ductless fume hood: Most operating costs for a ductless fume hood will come from filter changes. The amount of electricity the blowers consume should also be considered.
Ducted fume hood: The cost of operating a ducted fume hood can be calculated as a function of how much air the blower is exhausting. Thus working cost increases as a function of the volume of air (CFM) being moved. Therefore, reducing required CFM will help save on operating costs for ducted fume hoods. For instance, a ducted fume hood with a VAV system and automatic sash positioning system significantly reduces exhausted CFM and lowers your operating costs.
6. What accessories will you need for your fume hood?
Fume hood accessories include base cabinets, light fixtures, airflow monitors, electrical outlets, cup sinks, and service fixtures for water, vacuum, or gas. Terra Universal also offers cleanroom compatible lab tables and chairs for your bench top fume hoods.