How to Choose the Right Fume Hood for Your Lab

Choosing the right fume hood is crucial to ensuring safety from dangerous chemicals and vapors in your lab. The process of 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 right 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 type of work are you conducting inside your fume hood?

This worksheet will help you fill in the questions. 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 special 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 evaporating at a rate too fast for the fume hood to ventilate. This will lead to fugitive emissions that could migrate into the lab. The fume hood will ventilate the appropriate chemical solvents.

Evaporation rate is a function of temperature. Determine the normal temperature for the chemicals in use and if the chemicals 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 that are 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. If your application involves extra-large equipment, such as drum containers, a walk-in fume hood might be more appropriate.
Number of People: How many people will be working 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: Make sure your lab has ample height clearance for a larger 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 noxious 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 corrosive fumes and 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 recirculation of exhaust air. 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 radiologicals.

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 will need to take into consideration both operating duration and budget.

Constant air volume (CAV) fume hoods provide a constant airflow regardless of sash position. The blower will pull a constant airflow regardless if the sash is lowered. Lab hoods with CAV systems are ideal for light duty performance, however in general are less energy efficient compared to 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 increases the sash is raised. The decrease in overall airflow results in higher energy efficiency and lower operating costs.

5. What are the install 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). A ductless fume hood on the other hand recirculates air back into the lab and therefore does not require an HVAC system to exhaust fumes.
Operating costs:

Ductless fume hood: The majority of operating costs for a ductless fume hood will come from filter changes. The amount of electricity consumed by the blowers should also be taken into account.
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 operating cost increases as a function of volume of air (CFM) being moved. Identifying ways to lower 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 greatly reduces exhausted CFM and therefore 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 lab chairs for your bench top fume hoods.