Step 7: Attach duct takeoffs according to the table below. Insert the tabbed end of the takeoff
into the plenum and bend the tabs to make a secure fit. Finish with tape and mastic for an
airtight seal.
Air handler model
# of takeoffs
Diameter takeoff
BMKH12CD1
Up to 2
6” takeoff
BMKH18CD1
Up to 3
6” takeoff
BMKH21CD1
Up to 3
7” takeoff
BMKH24CD1
Up to 4
7” takeoff
Step 8: Attach the Supply plenum to the concealed duct, fitting around the flange. Attach with
foil tape, seal with mastic. Option - use sheetmetal screws into the flange for a more secure
attachment. Still use tape and mastic for air sealing.
Step 9: Attach the Return plenum over the return opening. There are no flanges on the return
side, but the Return plenum is the same size as the unit chassis, and can be taped on directly.
We recommend that you remove the filter screen and reattach further upstream in a location
you can access for maintenance, such as the return register.
Note: Ductboard is subject to minor tears and dents in shipping, or while being worked. These
can easily be patched with foil tape. A good, airtight plenum is the most important
consideration.
