- Q.We are renovating a 1980
home. The hvac sub says that since older fiberglass
duct board disintegrates from the inside out, all of
the ducts should be replaced. Could this be
A.Jeri Donadee, vice
president of H.B. McClure, a heating and cooling
contractor in Harrisburg, Pa., responds: When
duct board in a crawlspace or attic is not sealed
with UL 181 duct tape, condensed moisture can
accumulate near unsealed duct joints, leading to
duct deterioration. If such deterioration is
severe, replacement of the ducts may be necessary.
But it is unusual for properly installed duct board
to "wear out."
Your subcontractor’s diagnosis can be
easily confirmed by a visual inspection. Simply cut
open a section of duct and look at the interior
surface to see if there is any flaking. If the duct
is sound, be sure to reseal the duct using
appropriate UL 181 mastic or tape.