Bathroom Ventilation Fans for Dry Climate Homes

The rattle of a fan that has run for twenty years with nothing coming out of the vent is the first sign of a duct that has fallen off its collar, and the figures kept at riverside kitchen and bath remodeling touch diva start from that attic. A bath in Riverside, CA still makes steam on a winter morning, and a kitchen and bath remodel is the time to move that steam outdoors.

Why a dry climate still needs a fan

Riverside has little rain and low humidity for most of the year, but a hot shower puts a bathroom at full humidity within minutes. Cool mornings and mild winters with occasional freezes make that moisture settle on the mirror, the window and the ceiling paint. A fan carries it out before it reaches the framing, the caulk and the grout.

Old fans that vent into the attic

Many postwar houses have a fan, or no fan at all, that blows air straight into the attic space. In summer the attic is hot and dry enough to hide the problem. In winter the moisture lands on the underside of the roof and on the insulation. Opening the ceiling during a remodel is the moment to run real duct out to the roof or the soffit.

Sizing the fan

A fan is rated in cubic feet per minute. A common rule of thumb for a small bathroom is one cubic foot per minute for each square foot of floor, and large bathrooms with a separate toilet room or a big shower enclosure want more. A fan also has a sone rating, which is its loudness, and a fan that is loud gets turned off. A quiet fan sized a little large runs longer and does more.

Duct run and termination

Short, straight, rigid duct moves more air than a long flexible run with sags in it. The duct should slope slightly toward the outside and carry insulation in a hot attic, so condensation does not form inside it. A roof cap works, and a soffit vent works if it sits well away from the attic intake vents, so the moist air is not pulled back in. Attics in Riverside get very hot in summer, and wildfire embers are a reason to choose a vent cover with a screen.

Controls and timing

A fan wired to the light shuts off too soon. A timer or a humidity sensor keeps it going until the room is dry. Tile, a membrane and waterproofing last longer in a room where the air actually leaves, and caulk stays clean and white instead of turning gray along the tub.