Attributes . Efficient one-piece polypropylene impeller blower wheel; Attractive white polymeric grille with torsion springs to adjust for thickness variances in ceiling or wall; Polypropylene weather damper; Mounts on either 16 IN or 24 IN on-center joist or stud; Discharge is through 3 IN round duct through roof or wall; Sturdy mounting brackets of double metal thickness slotted on housing for vertical mounting adjustments; Extra large outlet box area; Not for use in kitchens; 1 YR warranty . Names