Introduction
For those interested in mycology, both amateurs and veterans know how important cleanliness is to stop contamination. I have run into contamination issues, forcing me to abort whole grows that were otherwise fine. Traditionally, laminar flow hoods fix this issue, filtering out microscopic contamination, but they are expensive and bulky. Luckily, I’ve discovered a quick and easy way to reduce or eliminate contamination significantly. It will take minimal tools, a few hours, and less than $100. This post will give you everything you need to make the best DIY budget Laminar flow hood. This proven design passes the flame test (shows proper laminar flow) up to 7.5 inches away. The HEPA filter is suitable for 2,000+ hours and can be easily replaced for as little as $18. Every agar dish was 100% successful, and the particle count results are irrefutable proof. The flow hood allows ZERO particles >1µm (one micron) in size through (for reference, Trichoderma spores are typically 3 to 5 µm in diameter).
(Note that I may make a commission through some affiliate links.)
Materials & Methods
- 64 qt Sterilite tub
- HEPA filter
- Multi-Speed fan
- Bolts
- Washers
- Silicone
- Course Sandpaper
- Caulking Gun
- Drill
- (Any Cutting Tool)
- Rotary Tool or
- Jig Saw or
- Woodburning Cutter or
- Soldering iron
- Marker
- Screwdriver
- Hole Saw
How to Build
- (PLEASE READ ALL INSTRUCTIONS FIRST)
- Temporarily place the filter inside the tote where you want it to go, then trace out the outline of your filter on the side of the tote. You only want to trace out the actual filter part, not the frame
- Use a cutting tool to cut along the lines. Go slowly and be careful not to crack the tub. Heating drill bits with a torch helps, and using angled tin snips worked fine for all of the cuts in this project, but I used a rotary drill and hand saw.
- Put the fan unit against the smallest side of the tote, with one end pushed up against the side of the tote, trace out the fan’s circle, and cut the circle out, ensuring the fan can fit through the hole.
- Put the fan into the hole you made in the tote with most of the fan inside the tote and a half inch of the fan sticking out the side (see below picture). Alight the bolts of the fan with the side of the tote, and mark the location of these bolts. Take the fan out, then drill holes only slightly larger than the diameter of your bolts where you marked.
- Use sandpaper or a file to smooth all edges where you made cuts in the tote. Use sandpaper to roughen the plastic around the holes that you cut. Then, clean the tote thoroughly with wet wipes or wet paper towels.
- Put the fan unit back inside the tote, with only a tiny bit sticking out the side. Use the new bolts and washers to bolt the fan to the tote. Use the caulk gun and silicone sealant to put a bead of silicone all around the outside of the fan housing where it passes through the tote. Get it from both sides of the tote (inside and out).
- Next, roughen the filter frame’s front, top, and bottom with sandpaper. Be careful not to touch the filter, wipe clean, then put a bead of silicone all around your filter frame and on the bottom. Stick the filter inside the tote with the front pressed into the area you cut out. Then, gently use both hands to push the tote from the front and filter frame from the back to seal them together. Add even more silicone sealant to the top of the filter where it meets the tote, down the sides of the filter frame inside the tote, and the back bottom edge where it touches the laminar flow hood.
Cut a small notch in the back top of the flow hood for the fan cord to come out, then put silicone sealant all around the top lip of the tote and heavy where the slit is for the fan cord, then put the tote lid on and latch the handles down. Let it all dry for 24 hours!
Conclusion
Remember to use a clean procedure for your new flow hood. This includes turning off your home heating/cooling system to prevent forced air from blowing into the room while you work, washing your arms and hands thoroughly, wearing a face mask, new nitrile gloves sprayed down with isopropyl alcohol, and working more toward the center of the flow using an elevated surface such as a wire cooling rack. Remember, the air at the filter’s edges is turbulent and not completely filtered. Keep your work as close to the filter as possible without touching it. Never put your fingers/hands in between the filter and your workpiece. Only keep agar dishes open as long as necessary.
Note: With this design, the air becomes turbulent about 7.5 inches away from the filter. Also, turning the flow up to max causes turbulent air. Using a lighter, you can check that the flame bends at about 45 degrees and remains “steady.” That is an excellent indicator of laminar flow. You will see the flame shaking in all turbulent zones. Where the flame shakes, you can expect high particle counts. Where it is steady, zero particle counts. If you hold your hand up near the filter, you should barely feel the breeze. You can fine-tune the flow rate very quickly with a lighter. If you used all of the same components I did, this would be at the fan setting directly in the middle between “M” and “H.”
Keep the flow hood covered when not in use to prevent dust from blowing around your room from landing on the filter. Always turn the flow hood on before removing the cover, and replace the cover while the flow hood is still on (turn it off after the cover is in place). It’s also a good idea to work in the smallest room and let the flow hood run for at least 15 minutes before you begin working. This will clear the air of all small particles in advance and keep your DIY laminar flood hood in working order.