Step 4: Make the Plenum
- Cut your cardboard tubes to 12 inch lengths (you will need about 18).
- Experiment with inserting them into the end of your tunnel to see how they fit best.
- Once you have found the best way to put them in, take them out and hot glue them together.
- Insert the plenum into the end of the tunnel that will be attached to the fan. If it is loose, secure it with duct tape or hot glue.