Bathroom Exhaust Fans:
Missing, Dead, Too Weak, Too Loud, or Never Turned On

A bathroom with no fan

The model residential code lets a bathroom rely on an openable window of a certain size instead of a fan. That’s how a lot of older Portland-area bathrooms got built, and some newer remodels too. Many newer codes and local rules call for a fan regardless.

Russ writes up bathrooms that rely only on a window. One of his Oregon City reports put it directly: a basement bathroom with only a window for ventilation is inadequate for moisture control. In January, few people open the bathroom window after a shower. The steam goes into the walls, the ceiling and the window frames instead.

Missing fans in his reports turned up in basement bathrooms, second-floor hall baths, primary suites and one tub area in a Vancouver master bath. Bathrooms added in basements and attic conversions are the usual suspects, because the fan and its duct are extra work.

Fans that don’t run, or run loud

A fan that doesn’t respond to its switch is the simplest finding. Russ found dead bath fans in Vancouver and Woodburn. Sometimes it’s the motor. Sometimes it’s the switch or the wiring.

Noise came up more often. Fans in Portland, Lake Oswego, Sandy and Vancouver made grinding, rattling or unusual startup noise. That usually means a worn motor bearing, a loose housing or a damaged blade. A loud fan isn’t dangerous by itself, but it’s a fan people turn off after a few seconds, and a fan that runs 10 seconds does almost nothing.

Fans are rated for noise in sones. A rating around 1 sone or less is quiet enough that most people will leave it running. Older, cheaper fans are often several times louder.

Odd controls show up too. In one Battle Ground house, a ventilation fan in the hallway ceiling had no visible switch anywhere. A fan nobody can turn on is the same as no fan.

Weak fans and bad ducts

A fan can run and still move very little air. The rated cfm on the box is measured with little or no duct. A long run of flex duct, several bends, a crushed section or a stuck damper can cut that a lot.

Russ’s reports had a few of those behind the ceiling. A Lake Oswego bathroom duct had come apart in the crawlspace. A Gresham duct had pulled off the roof stem. In one Beaverton bathroom, part of the duct was scrap material held together with tape. In Sherwood, the damper flaps on the outside caps were missing.

For sizing, the Home Ventilating Institute suggests about 1 cfm per square foot of floor for bathrooms up to 100 square feet. The residential code minimum for a fan that runs on demand is 50 cfm. A 50 cfm fan at the end of a long duct in a large primary bath is often working well below what the bathroom needs.

The tissue test is a rough check you can do yourself. Hold a single square of tissue near the grille with the fan on. A working fan pulls it flat against the grille.

Installation details that let moisture in

Some fan findings are about the housing. In Springfield and Gresham, the fan housing wasn’t flush with the ceiling, leaving a gap around it. That gap lets warm, wet air go straight into the ceiling cavity or attic around the fan instead of through it. Missing grilles (Lake Oswego, Portland) leave the housing open.

Wiring at the fan came up twice, in Vancouver and Gladstone: the cable entered the fan housing without a connector or bushing, so the wire rubs on the bare metal edge of the knockout. That one goes to an electrician.

What too little ventilation leaves behind

The clues show up in the bathroom itself. Peeling paint on the ceiling, especially over the shower. Mold-like spots on the ceiling, the caulk or the window frame. A Sandy primary bathroom had apparent mold on the window, and the report recommended cleaning it and making sure the fans exhaust properly. Grout that keeps growing dark spots, which the post on water behind shower tile covers. Doors that swell and stick.

Skylights over a bathroom make it worse, because the shaft carries the steam straight up to the coldest surface in the room. The skylight post covers that. When there’s visible growth, the mold finding guide covers what happens next.

What Russ checks

In each bathroom he notes whether there’s a fan, turns it on, and listens. He checks the grille and housing, looks for signs of moisture in the room, and follows the duct in the attic or crawlspace when it’s visible and accessible. He doesn’t measure airflow with an instrument. When a fan is missing, dead, noisy or not ducted properly, the report recommends a qualified contractor or electrician.

For the rest of the room, the guide to what to look at in the bathrooms before you make an offer covers plumbing, tile and the toilet. To set up an inspection, you can book online.