I put together a fairly cheap but fairly large (2'x2'x8" workspace) laminar flow hood for keeping a sterile environment at home. I already had the fan and some of the hardware, and I found a good filter cheap, so I only ended up paying $190 to build it.
Parts and Tools
-($100-200) 2'x2' H15 HEPA Filter. I was able to find a $100 24"x22" h15 HEPA filter on ebay after browsing through manuals. There are cheap good filters out there if you want to wade through a bunch of unmarked auctions looking for an h15 one. Most sellers don't label it on the auction so you have to take the model number, google the manual, and look it up there. The dimensions of the hood are totally determined by the filter you pick, so keep that in mind while shopping.
-($50) Wood. You will need laminated wood. I got an 8'x4'x3/4" sheet and had it cut into the pieces I needed at the store.
-($200) 380CFM Fan - 6inch. I had an old one lying around I could use. You can figure out how powerful a fan you need based on your filter here.
-(<$40) Hardware. You'll need screws, wood glue, 6inch ducting, a small cheap prefilter (i got mine for $10 at home depot), aluminum tape, silicone caulking, and weather stripping. Make sure the glue you get seals airtight.
How to Build the Hood
First, check out the diagram below. It only shows the inside dimensions of the box, so you should draw your own diagram which includes the thickness of the wood and all of the dimensions so that your filter fits tightly inside. My filter was 24"x22" so I cut the sides 23.5"x24", the top and bottom 25.5"x24", and the back 25.5"x23.5". You can make it as long as you like, the longer it is from front to back the deeper your workspace will be.
1. First assemble the sides and back with the base with wood glue and screws.
2. Add fairings as shown in the diagram and attach your weather stripping to them.
3. Push your filter in, make sure it is snug! I screwed in a small wooden piece on the bottom to secure it.
4. Use the silicone caulking to seal all of the inside edges, including where the fairing meets the filter.
5. Cut a 6in hole for your fan on the top piece, and glue and screw it shut.
6. Through your 6in hole caulk the rest of the seams on top inside the hood. This part is hard!
7. Make sure you let everything dry in a well ventilated space.
8. Tape up the outside seams with aluminum tape, and attach your 6in ducting to your fan and seal with aluminum tape.
9. Tape the prefilter to the intake of the fan.
10. Test the hood with a lighter. It should push it 90 degrees at 1inch away from the filter evenly.
How to Use the Hood
We will cover this in a future blog post. Stay tuned!