Building a small fume hood for stinky projects

Step 9 Testing, testing

Turn it on, hear the whirr and watch the tissue paper blow in the breeze... so far, so good. Open a container of something stinky inside the enclosure, then get out the duct tape and get ready to play 'find that smell'. As I mentioned earlier, there were many, many small holes in the shroud of the range hood that was squirting out fumes. We sniffed out and patched dozens of leaks, basically covering the top and back of the shroud with tape. Don't forget to test all the way along the duct and whatever exhaust connection you chose. When you're done, you should not be able to smell any fumes at all.

Time for a proper test. Do a test batch of whatever stinky project you built the hood for. This will produce much more stink than just an open container, so go around and check for leaks one last time. Once you are satisfied that it's sealed, you're done! Enjoy being able to do your stinky projects indoors!

(Aside: As I mentioned earlier, the small duct we had installed at first could not handle the full flow rate so the face velocity was too low to keep everything in. It still worked reasonably well, but the smell of the resin was perceptible.

The volume of air that a duct can carry scales with cross-sectional area; our duct is circular so the area scales with the square of the diameter. That means that using a 3" duct rather than 4" cuts the diameter by 25%, which cuts the duct capacity down by about 44%! Oops, an embarrassing oversight... I ended up having to go back out and find a 4" duct after all. Once I replaced the small duct with one of the proper size, we tested it again... success! We could no longer smell the fumes!)

Comments

[ttodorov]

I am looking for something like that, albeit on a bit smaller scale. I'd like to use it for etching PCBs with ferric chloride. While I was reading your post, I was thinking about what I'd do different and decided to offer a suggestion you might want to consider. In particular, why not use silicone instead of so much duct tape. Depending on the quality of the duct tape, a tube of silicone is about the same price or cheaper. It also seals better and offers greater stability and less prone to "un-sticking" over time and changing temperature conditions than tape. What I can't say is, if the fumes from the resin curing are more detrimental to tape glue or cured silicone...

And another thought. Why not cut out most of the thin angled front part of the hood (I would leave juts 5 inches on each side for fitting over the wooden box and stability) and glue another plexiglass sheet cut to size, so your wife can look straight down when working, without cranking her neck or stepping back to look and letting fumes escape through the front opening (read here: use silicone to stick the plexiglass to the metal :-)

[adam.coderre]

I agree that using silicone or some other caulk or sealant would at least look better than the duct tape. I was just going the quick-and-easy route with the tape. If I had to build this again I'd take your advice for that window, it would be a really nice addition.