A tight path to the outdoors keeps the indoors fresh and you can call it a day because you are one step closer to the Energy Star
The Energy Star checklist has a lot of items. Some of them relate to bathrooms.
Most bathrooms have bath fans, and this one has a light, too, and most bath fans have ductwork that directs moist air outside.
Bathrooms also have ceilings, and that is a place for air leaks to occur: between the edge of the fan and the hole cut for the ceiling.
Even after the hole is sealed, though air can escape the fan housing: if holes are not sealed. Use foil tape, foam, or caulk to seal these holes
For retrofit work, you can build a box over the fan—using drywall or rigid foam— with all the seams sealed. The hole for the ductwork can be plugged with low-expansion foam.
As long as you are sealing holes in the system, seal the connections and seams in metal ductwork using dust mastic—not duct tape. Because duct tape works for everything except ducts.
Outside is where the vent cap comes into play. That begins at the beginning—with house wrap on the wall. Cut a hole in the house wrap and then cut a hole in the wall sheathing. Cut a flap at the top of the hole, to overlap the vent cap flange, and make the vent cap appear.
BAM
Apply a bead of caulk to the back side of the damper flange, to bed the damper into the house wrap and insert the damper into the hole. Tape the side flanges with construction tape and fold the flap down. It’s best if the tape extends up to the top of the flap. Tape the sides of the flange to seal the corners.
A tight path to the outdoors keeps the indoors fresh and you can call it a day because you are one step closer to the Energy Star.
