If you are like me and do smelly chemistry experiments or experiments that generate nasty gasses, you probably need a fume hood. Unfortunately, a cheap one costs about $5,000 US and take up a lot of room. Although I wouldn't suggest this design for something like hydrogen sulfide or a NO2, it is very useful for everything else. All of the parts together cost about $30 US.
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Step 1: Required Parts
1. 58.4 cm x 41.3 cm x 3.4 cm plastic box with lid (Sterilite or such)
2. 4 inch x 5 ft vinyl laundry duct
3. AC 4 inch diameter PC fan with power cord
4. 4 bolts/nuts
5. One screw
6. Ring screw
7. Thick cardboard
8. Aluminium foil (opt.)
9. LED light strip with power cord (opt.)
Step 2: Cutting the Lid
Cut the bottom of the lid to your box off from the bottom to the top of the curved edge. Snap back on box. You can close the fume hood by snapping on normally or opening it by snapping it on the top. To help hold it in palce when open, screw a screw through the lid in the middle of the lid just above where it meets um with the side of the box. Screw a ring screw in the top of the box so the screw will slide right in and keep it open.
Step 3: Cutting the Box
Remove the lid and turn the box on the side opposite to the side with the lid. Using your own judgement, cut along what is now the bottom of the box to form a large opening, leaving a small amount on the sides for support. It helps to place painters tape around where you are cutting to prevent cracking the plastic. Use a drill with a bit to get started. Reinforce any cracks and the edge of the cut with hot glue.
Step 4: Installing the Fan
Place the fan on the top of the box and trace a line around the perimeter (on the box). Inside of the traced square, make a slightly smaller square for the air to escape. Using the same cutting method as before, cut out the inside square. Make sure the fan lines up and mark where you will drill your holes to attach the fan. Drill the holes and bolt the fan on the box, making sure that the air flow arrow is pointing upwards so you don't blow air into the hood. Slip the laundry duct over the top of the fan and secure with a large zip tie. If you haven't already, attach an AC power cord to your fan. Make sure you have a place to plug it in.
Optionally you can add a 12 volt LED lighting strip to the box behind the fan and drill hole for the AC/DC adapter. Just remember to seal it!
Step 5: Plumbing the Duct
Choose a window to put your fume hood by. Measure the height of the window and make a 6 inch wide strip of thick cardboard to fit the window. To insulate the cardboard further, cover it in aluminium foil. Towards the bottom of the strip, cut a 3 3/4 inch hole and fit about two inches of the other end of the duct through it. Open the window and put the cardboard with duct inside of it. Close the window on the cardboard.
Step 6: The End!
You now have a functional fume hood. It will pump any gasses or odors out of the window. Just remember, be very careful with chemicals and what gasses you are making in it. If you have any questions, feel free to ask in the comments.