Bathroom exhaust fan cost

Installing a bathroom exhaust fan costs $250 to $900, typically around $450. Replacing an existing one in the same spot is $150 to $400. Putting one where none exists, with new ducting to the outside and a new circuit, is $600 to $1,500.

It is the cheapest thing in a bathroom and the one that decides whether the paint, the grout and the framing last.

What it costs

Sizing it

Fans are rated in CFM, cubic feet of air moved per minute.

Above 100 square feet, add per fixture: 50 CFM for a toilet, 50 for a shower, 50 for a bath, and 100 for a jetted tub. A 120 square foot bathroom with a toilet, shower and tub wants 150 CFM.

The other number is sone rating, which is loudness. Under 1.0 sone is quiet enough that people leave it running, which is the entire point. A 4 sone fan gets switched off after ninety seconds and does nothing.

The three things that make a fan useless

It vents into the attic. This is extremely common and it is not ventilation. It moves warm wet air into the coldest part of the house, where it condenses on the roof sheathing. The result is mold in the attic and, eventually, rotten sheathing. Duct must terminate outside, through a roof cap or a wall vent, with a damper.

The duct is too long, too narrow or crushed. Flexible duct crushed against a joist or run 25 feet with four bends throttles a 110 CFM fan down to almost nothing. Short, straight, and 4 inch minimum, with smooth rigid duct if the run is long.

Nobody runs it. A fan needs to run during the shower and for 20 minutes afterwards, which is when the moisture actually leaves. A humidity-sensing fan or a simple timer switch fixes this for $80 to $250, and it is the best value item on this page.

Why it matters more than it looks

A shower puts a remarkable amount of water into the air. Without ventilation it condenses on the coldest surfaces: the window, the exterior wall, the ceiling, and inside the wall cavity where you cannot see it.

The visible consequences are peeling paint, black spots in the grout and a mirror that stays fogged. The invisible one is moisture in the framing, and that is a structural repair rather than a cleaning problem.

If you have a bathroom with no fan and no window, that is worth fixing before it is worth retiling anything.

Frequently asked questions

Is a window enough instead of a fan?

Code in many places allows it, and in practice it is not enough, because nobody opens a window in February. Fit a fan even where a window satisfies the inspector.

Can I replace a fan myself?

Replacing a unit in the same housing, if the wiring and duct are already there, is a realistic job for someone comfortable turning off a breaker and working overhead. New ducting through a roof is not, and a new circuit is an electrician.

Where should it vent to?

Through the roof with a proper cap, or through a gable or side wall. Never into the attic, never into a soffit vent directly under an intake, and never into a wall cavity.

How long do they last?

Ten to twenty years. The bearings dry out and it gets louder first, which is the useful warning sign. A fan that has become audible from another room is on its way out.

Should I get one with a heater?

In a cold climate they are genuinely pleasant and they draw a lot of current, typically needing a dedicated 20 amp circuit. If the wiring is being done anyway, it is a good time. Retrofitting the circuit alone is $300 to $900.