Bathroom fan, lighting, and moisture: vent outdoors, then see the floor

Steam on the mirror is the easy tell. Paint peeling at the ceiling, a fan that screams and still leaves the room wet, and a night trip to the toilet with the overhead on full are the same room, three jobs.

You’re looking at fixtures and layout. A fan that actually moves air outdoors. Light you can see the floor by at 2 a.m. without waking up dizzy. This page does not diagnose mold, lungs, or what a doctor would call a moisture-related illness. If the drywall is soft or you smell something you cannot place, get a contractor or a hygienist, not a louder grille.

What an aging-in-place bathroom costs is the wet-room budget. Lighting for fall prevention is the path from bed. This page is the ceiling box over the shower, and whether that box dumps into the attic.

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How big a fan, in CFM

CFM is cubic feet per minute, the amount of air the fan is rated to move. The Home Ventilating Institute (HVI) is the trade group that certifies those ratings. For a bathroom up to 100 square feet, they want about 1 CFM per square foot, which they describe as roughly eight air changes an hour.

Their 8-by-5 example is 40 square feet. On the bathroom-ventilation page that math lands at 40 CFM. On the “how much ventilation” page they also set a 50 CFM floor for rooms under 100 square feet, so a powder room still gets a real fan.

Over 100 square feet they switch to fixtures: 50 CFM each for a toilet, shower, or tub, and 100 CFM for a jetted tub. A 20-by-12 bath with a tub, a shower, and an enclosed toilet is 150 CFM on that table, either as one fan or as three 50 CFM fans where the steam actually is.

HVI: bathroom ventilation

HVI: how much ventilation do I need?

HVI wants the grille over or near the shower or tub, and its own fan in an enclosed water closet. They want the door undercut about 3/4 inch so makeup air can enter, or the fan is just fighting a sealed box. They want the fan to keep running 20 minutes after you leave. A timer or a humidity control is how that happens without you standing there.

Continuous ventilation at 20 CFM can stand in for a 50 CFM intermittent fan on that same HVI page. That is a low, always-on trickle, not a shower blast.

ENERGY STAR certified bathroom fans in the 10 to 89 CFM band have to hit at least 2.8 CFM per watt and stay at or under 2.0 sones. The 90 to 200 CFM band is 3.5 CFM per watt, still 2.0 sones. A sone is a loudness rating. Under 1.0 is the neighborhood people actually leave running. A 3-sone builder fan is why someone hits the switch off after 30 seconds.

They also want the fan to still deliver at least 70 percent of its 0.1-inch rating when you load it to 0.25 inches of water, because real duct is not a lab box.

ENERGY STAR: ventilating fan criteria

Panasonic’s WhisperCeiling DC FV-0511VQ1 is a common ENERGY STAR pick-a-flow unit: 50, 80, or 110 CFM on a switch, listed under 0.3 sone. That covers a small powder room through a typical 5-by-8 or 7-by-10 bath without buying three SKUs. It is still only as good as the duct.

EPA’s indoor-air page is blunt about the path: a bathroom fan only helps if it exhausts outdoors. A grille that blows into the attic is a moisture dump into insulation.

EPA: improving indoor air quality

What the install actually costs

Angi’s 2026 bathroom-fan page, updated September 10, 2026, puts the national average at $396 from 2,554 verified projects, with most jobs $120 to $900. Fan-only hardware on their size table runs $20 to $250 at 80 CFM or less, $50 to $325 at 80 to 99 CFM, $55 to $400 at 100 to 150 CFM.

A new wall vent is $250 to $800. A roof vent is $350 to $950. Those lines are why two quotes for “a fan” are not the same job. One is a swap in an existing hole. The other is a roof jack and flashing.

Angi: bathroom fan installation cost (2026)

Fixr’s install guide puts a first-time fan at $250 to $900, average $400. A replacement in the same opening averages about $200, in a $150 to $500 band. Labor they put around $150 for a swap and $250 to $500 for a first install. A moisture-sensing, high-end unit can land near $1,000.

Fixr: bathroom exhaust fan installation cost

If one bid is $180 and another is $1,100, ask which one includes the outdoor cap. A cheap grille on a crushed 3-inch flex hose in the attic will still leave the mirror wet.

Light is a different switch

NIA’s room-by-room fall list wants a bathroom light on at night, or a night light that comes on in the dark. AARP’s nighttime guidance is low-level pathway light, not the vanity on full. That is already on the lighting for fall prevention page, with HomeGuide’s fixture bands: ceiling lights $70 to $250 installed, a basic fixture job $133 to $414.

A fan-with-light combo is one ceiling hole. It is also one switch unless you pull a second hot. People then run the noisy fan to get the light, or they sit in the dark because the fan is too loud. Split them when you can: a quiet fan on a timer or humidity control, and a separate night light or dim vanity that does not start the motor.

Bright white at 2 a.m. is how people wake up enough to be unsteady. Warm, low light at the floor and a brighter light for shaving are two products. The combo unit that only has “on” is the wrong product for that split.

Grab bars and a taller toilet still matter more than a prettier grille if the tub is the daily problem. The under-$2,000 band is bars, levers, and the toilet you already have. The fan is how that room dries after the shower, not a substitute for a rail.

What usually blows the moisture job

The duct ends in the attic. You can have a 110 CFM ENERGY STAR fan and still soak the insulation. EPA wants the exhaust outdoors. Ask to see the cap on the roof or the wall hood. If the contractor cannot point at it, you do not have a fan yet.

The fan is loud, so nobody runs it. ENERGY STAR’s 2.0-sone cap is the ceiling for a certified unit. HVI’s 20-minute after-run only works if the thing is quiet enough to leave on. A humidity switch or a timer is the control. A wall switch you forget is how the paint peels.

The door is weatherstripped to the tile. HVI’s 3/4-inch undercut is makeup air. A tight door plus a strong fan pulls combustion air from a nearby water heater or makes the fan stall. That is a layout question for the electrician and the HVAC person, not a bigger motor.

CFM on the box, 4-inch flex, three elbows, 20 feet. ENERGY STAR’s 70-percent-at-0.25-inch test exists because long, cheap duct eats the rating. Short, smooth, the diameter the fan was built for, insulated in a cold attic so the duct does not sweat.

A heater-fan-light on one circuit. Fixr’s high end near $1,000 and Angi’s roof-vent band are where that combo lives. The heater often wants its own circuit. Treat heat as a separate quote.

Painting over the stain and leaving the attic dump. The stain comes back. The fan job is the duct and the minutes after the shower, not a new gallon of ceiling paint.

What the driveway questions sound like

Where does this duct terminate, on the roof or a wall, and can I see the cap from the yard?

What CFM is on the HVI label, and did you size it to this room’s square footage or to the fixtures?

How many sones at the CFM you are selling, not at the quietest speed on the brochure?

Does the control keep the fan on 20 minutes after the light goes off, or is it a single switch?

Is the night light on a separate hot, so the fan can stay off at 2 a.m.?

Who patches and paints the ceiling, and is the roof jack the electrician or a roofer?

How do I decide this week?

Measure the bath. Under 100 square feet, start at 1 CFM per square foot and do not go below 50 CFM. Over 100, add HVI’s fixture numbers.

Price a swap and a new vent as two jobs. Angi $396 average is a mix. Fixr’s replacement band is $150 to $500. A roof cap is the extra invoice.

Confirm the air leaves the building. EPA is the outdoor-exhaust rule. An attic dump is a moisture problem with a pretty grille.

Put the fan on a timer or humidity control so it runs 20 minutes after you leave, which is HVI, not a brand trick.

Keep night lighting off the fan motor. The 2 a.m. path is the lighting page. The shower steam is this one.

If the tub is still a climb, the fan will not fix that. Price grab bars and the bathroom budget next, and leave the ceiling fan as the drying job it is.