Replace Return Air Systems That Use Building Cavities

Select duct materials:

with a flame spread of no more than 25 when tested in accordance with ASTM E84 or UL 723 and that are UL 181, SMACNA, or NAIMA approved or conform to ASTM A653

Close and seal existing return air openings in accordance with SWS detail for "Duct Repair: Mechanical Fastening" and SWS Subtopic "Duct Sealing"

Provide alternate return air opening to the furnace closet (e.g., louvered door or install grilles)

Net free air flow must minimally meet manufacturer specifications for the installed equipment

Seal entire return cavity with durable materials and UL 181 approved mastic and mesh tape (i.e., no foam allowed inside return systems)

Provide accessible filter grill and filter with no air bypass of the filter