There are ductless vent fans that use a charcoal filter to remove odors but they do not remove excess moisture which is the main purpose of a bathroom vent fan.
Venting bathroom exhaust fan through wall.
If you vent through the roof condensation will drip back into the interior.
No matter the location of the bathroom you can vent the exhaust fan through the wall.
I recommend that my clients vent their bath fans out a gable wall if at all possible when not using an hrv or erv that is.
The exhaust duct using solid metal steel in this case is routed through the ceiling out over the wall top down through a soffit or roof eaves overhang and then enclosed against pest entry.
There aren t many options for routing an exhaust fan to the outside of the house.
Ductwork is what will connect the fan to the outside.
If your exterior siding is vinyl or fiber cement you will have an easier time cutting the hole.
If you vent through a soffit where attic vents are often located the moisture will get sucked back up into the attic or roof venting.
Amazon s choice for through wall bathroom exhaust fan broan nutone 512m through the wall ventilation fan white square exhaust fan 6 0 sones 70 cfm 6 4 5 out of 5 stars 765.
Wall mounted vent fans are available though they re not as common as ceiling mounted models and may be more difficult to install especially if you have a brick veneer house.