8 Ways Your Fume Hood Spec Could Be a Mess

by Rand Weyler

We've all been there - stressing over getting the details correct for the client!
Here are 8 things to look for in your own Fume Hood Spec.


1. Does your spec mention auxiliary air?
Whoa, the 70’s called and wants their spec back! This technology is not used in today’s labs. It utilizes extra ductwork, making it expensive, not to mention the problems regulating the comfort of the user on a hot, humid, or cold day. We don’t pump outside air in front of hoods anymore. If you see the word “auxiliary” you haven’t changed your spec in decades.


2. Did you include hood field testing?
All hoods should be certified in the field because the hood location as well as HVAC design can negatively affect fume containment. Specify that all hoods are tested by a third party for unbiased results. Companies like ENV Services or B&V Testing Inc. specialize in ASHRAE-110 testing so they will likely be faster and more experienced than the hood manufacturer or distributer. Include the pass/fail criteria set forth in the national code ANSI Z9.5 for “As Installed” (4.0L AI 0.10ppm).

 3. Are you specifying the amazing front-loaded valves?
I know that was a “loaded” question, but service valves such as air, nitrogen, argon, vacuum, and any other variety required will eventually need service or replacement. There are two kinds of remote controlled hood valves, front-loaded or rod-driven. The front loaded valves can be serviced from the front of the hood. This eliminates the expense of emptying the hood, decontaminating the hood, and requiring the plumber to climb inside to remove a service panel to then service a clogged vacuum valve for instance. Rod-driven valves may be a tiny bit less expensive now, but not worth the aggravation later.


4. Did you specify an epoxy liner?
99% of the fume hoods we sell have an FRP (Fiberglass Reinforced Polyester) lining. Why? Three reasons, it’s white, it’s inexpensive, and it is resistant to more chemicals than other potential liners. Specialty hoods like a radioisotope hood or a perchloric acid hood may require a coved-corner stainless steel liner for cleaning, but there doesn’t seem to be a good reason for using epoxy as a liner material. It’s heavy, typically more expensive, and doesn’t stand up to chemicals as well as the FRP.

5. You specified “high performance” right?
It sounds great, but not every hood application will benefit from low flow or high performance. These high performance fume hoods run around 60 ft/min and can save energy when set up on a variable air system when multiple hoods occupy the room or building. Typically, if this is the only hood in the room or at the facility it can simply be designed as part of the room’s exhaust and operate at 100 ft/min without wasting any additional energy. If you are designing one hood in a high school chemistry lab, there is no need to spend extra money on a high performance hood.


6. Why wouldn’t I want an explosion-proof hood?
Well, because there is no such thing! If your spec even mentions the words “explosion-proof” then it may not adequately describe the hood’s electrical requirements. Rooms can be electrically classified “Class 1, Division 1” or “Class 1, Division 2”. Understanding how the electrical fixtures are separated from the hood chamber could save your client lots of dough if the room the hood is in is not classified this way. There is one thing I can assure you; no hood is “explosion-proof”. Don’t make me prove it!

7. Chain, Belt or Cable Sashes?
This question has lingered for at least 18 years (which is as long as I have been in the fume hood business). High quality cables are sometimes required for certain hood sash configurations, but it is rare that a manufacturer couldn’t provide a chain or a notched belt-driven sash. Unlike cables, sashes on chains (think bicycle) or notched belts travel smoothly as both sides raise and lower at the same rate when sprockets at each end of the sash are connected with an axle. While cables and belts stretch and break, a chain will never fail you.

8. Did you specify the intended airflow criteria?
It is surprising to me how many specifications don’t mention the hood performance criteria properly. We can’t build, test and certify (or bid on) a hood without knowing the intended face velocity at the intended sash opening size. And once that is known, the bidder needs to know if the hoods will be connected to a constant volume (CAV) or variable volume (VAV) system. Typical industry standard for a bench hood is 80 ft/min at 18” open on a VAV system, but of course this widely varies. Knowing the criteria helps clarify if other areas of the spec are accurate, which makes this the most important information that your hood spec can tell us.

Topics: Lab Fume Hoods, Lab Best Practices, High Performance Fume Hoods