Step 1. Using a serrated knife, cut to separate the Supply and Return plenums. Using the
pre-marked line will give you a 30” Supply and an 18” Return. You can make your own marks
and change the length to suit your particular installation.
Step 2. Lay out the Supply plenum with foil backing side down. Fold along the V trench cuts to
create a box shape. Align the backing-only lap joint as shown to create a box with rectangular
shape.
Step 3: Use foil tape to close up the plenum. Be sure the joint is as depicted above, and the
resulting plenum shape has 4 right angles.
Step 4: Attach the end cap by inserting the insulation side into either end of the supply plenum.
If the fit is too tight, use your serrated knife to bevel the insulation until you get a nice snug fit all
the way around. Use the backing overlap to make a good taping surface and secure with foil
tape. You now have a 5 sided supply plenum, ready to attach to the supply opening of your
concealed duct unit.
Step 5: Repeat Steps 2 and 3 to create a Return Plenum.
Step 6: Use the serrated knife or ductboard hole cutting tool to cut holes for attaching duct
takeoffs.
