Kitchen and bath
Bathroom exhaust fan replacement cost
A new 1-sone fan in the same opening is about $446 fitted; a retrofit motor in the old housing $266; a bigger fan in a bigger hole $662; a first installation $1,043. And the sizing the shop does not do: a 40 sq ft bathroom needs 50 CFM, but on 12 ft of 4 in duct with two elbows a 50 CFM fan delivers 33 — the one to buy is the 80. Plus the rule that rots roofs: it has to vent outside, not into the attic.
Written and edited by Pablo Ruiz Quintero
Last reviewed 2026-09-23 · Nothing you type leaves your browser
Bathroom exhaust fan replacement cost calculator
The room, the duct, and what is in the ceiling
The fan is chosen after the duct, not before: the duct decides how much of the number on the box gets outside.
50 CFM needed.
Up to 8 ft: by floor area.
Fixtures that make steam. Counts over 100 sq ft.
An ordinary tub is 50.
The old housing comes out, a new one goes in the same hole, and the duct and the wiring reconnect. From the attic it is an hour; from below, with the housing screwed to the joist through the opening, a little more.
The duct
Look in the attic, or follow it from the grille. Every elbow counts as 15 ft; the cap as 10.
Standard, and it chokes long runs.
52 equivalent ft with the elbows and cap.
Fan delivers 65% of its rating.
The shortest run from most bathrooms and the one that leaks: a cap flashed under the shingles, sealed, with a damper. It is a roofer's detail done by an electrician, and it is where to look first when the ceiling stains.
Keep the existing duct.
A sone is the noise of a quiet refrigerator; this is the fan people leave running, which is the fan that actually dries the bathroom.
On with the light, off with the light. The fan runs while you are in the room and not for the twenty minutes after, which is when the moisture is.
By the hour plus the trip.
Worked from above.
Used only to pick a regional labour rate. It stays in your browser.
New fan, same-size opening
$446
buy a 80 CFM fan · delivers 52 on this duct · room needs 50 · 1.5 h
Why not the 50 CFM fan the rule names
The box is rated at almost no resistance. 12 ft of 4 in duct, 2 elbows and a cap is 52 equivalent feet, and on that a fan delivers about 65 per cent of its rating — a 50 would give 33. The 80 is the first catalogue size that gets 50 outside.
The rule that rots roofs
It has to go outside.
Not into the attic, not into the soffit cavity, not to “near” a roof vent. Shower steam blown into an attic condenses on the underside of the roof deck every morning, and the black stain above the bathroom is the wood rotting. The code says outdoors, and it is the first thing an inspector puts a hand up to check.
The same fan, the four jobs
| Motor and grille in the old housing | $351 |
| New fan, same-size opening | $446 |
| New fan, larger opening | $662 |
| First installation — no fan there | $1,043 |
Same fan, same duct settings. What is in the ceiling is the price.
What the duct does to the fan
Every catalogue size, on the box and on your duct.
What to buy, and what the visit costs
- 80 CFM fan, 1 sone
Delivers about 52 on this duct, against the 50 the room needs. A sone is the noise of a quiet refrigerator; this is the fan people leave running, which is the fan that actually dries the bathroom.$143 - 1.5 hours of an electrician
The old housing comes out, a new one goes in the same hole, and the duct and the wiring reconnect. From the attic it is an hour; from below, with the housing screwed to the joist through the opening, a little more.$143 - Trip charge
Two bathrooms on one visit share it.$160
What it costs
National average. A 80 CFM, 1-sone fan, new fan, same-size opening. Not included: a new circuit, roof repairs beyond the cap, or a fan with a heater, which needs its own 20 A circuit.
The switch is usually taken from the light’s box; if the bathroom needs its own circuit, that starts at the panel, and the ceiling around a larger opening is closed at the rate on the drywall repair page.
Worth knowing
- The room needs 50 CFM — one per square foot, with the 50 CFM minimum. But the 80 CFM on the box is measured at almost no resistance, and 12 ft of 4 in duct with 2 elbows and a cap is 52 equivalent feet: this fan delivers about 52. The 50 CFM fan the rule seems to ask for would deliver 33.
- At 52 equivalent feet, a 4 in duct is costing this fan 35 per cent of its rating. A 6 in duct on the same run would let a smaller, quieter fan do the job — and if the duct is being replaced anyway, the price difference is $14.
- On the light switch, the fan runs while you are in the room and stops when you leave — which is exactly when the moisture is. A timer switch is $30; a humidity sensor $48. Either one changes how the bathroom smells more than the fan does.
On this page — 4 sections
The duct is the fan
The short version
- The room needs 50 CFM. Buy the 80. The duct takes 35 per cent of the box number.
- Four jobs with one name. Motor $266, same hole $446, bigger hole $662, first time $1,043.
- It has to go outside. Into the attic is illegal and it rots the roof.
- A timer switch is the best $30 on the page. The moisture is there after you leave.
The number on the box — 50, 80, 110 CFM — is measured with almost nothing attached to the fan. Attach 12 ft of 4 in duct, two elbows and a roof cap, and the fan is pushing against 52 equivalent feet of resistance, and it delivers about 65 per cent of what the box says.
So the rule that says a 40 sq ft bathroom needs 50 CFM is right, and a 50 CFM fan is wrong: on that duct it delivers 33. The fan to buy is the first catalogue size whose derated airflow meets the room’s number — the 80 here — and that is the calculation the calculator does and the shop does not.
equivalent ft = duct ft + 15 × elbows + 10 for the cap
- ≤ 25 ft on 4 in duct
- the fan delivers its rating
- 25 – 50
- about 80 per cent
- 50 – 75
- about 65 per cent
- over 75
- about half — or a 6 in duct
Worked through — 12 + 15 × 2 + 10 = 52 equivalent feet: 65 per cent. The room needs 50, so 50 ÷ 0.65 = 77, and the first catalogue size above that is the 80.
| 4 in duct | 6 in duct | |
|---|---|---|
| The same 12 ft run, two elbows | 65% of rating | 85% of rating |
| Fan to buy for 50 CFM | 80 CFM | 70 CFM |
| A 30 ft run with three elbows | 50% | 85% |
| Fan to buy on that run | 110 CFM | 70 CFM |
Home Ventilating Institute / ASHRAE 62.2, Bathroom exhaust sizing and certified airflow ratings · checked 2026-09-23
It has to go outside
Half the bathroom fans in the country blow into the attic. It was easier, nobody looked, and the fan “works” — the mirror clears. What it does is put a shower’s worth of steam against the cold underside of the roof deck every morning, where it condenses, runs, and rots the sheathing from the inside. The black stain above the bathroom in any attic is that.
The residential code says outdoors — not an attic, not a crawl space, not a soffit cavity — and an inspector checks it by putting a hand above the fan. On a replacement where the old duct goes nowhere, the duct and the cap are not an upgrade: they are the installation the last fan never had, about $257 on top of the fan.
80 CFM
Buy, for a 50 CFM room
On 52 equivalent ft
33
What a 50 delivers
On the same duct
$257
Duct and cap it never had
When it vents into the attic
$160
The trip charge
1.5 h of work
International Code Council, IRC M1501.1 — Outdoor discharge, and M1507.4 — Local exhaust rates (2021) · checked 2026-09-23
Four jobs with one name
If the brand sells a retrofit motor for the housing in the ceiling, the job is fifteen minutes from below — no attic, no drywall — and a handyman does it for about $266, most of which is the trip. If the housing changes but the hole does not, it is an hour and a half for an electrician: $446. A quieter fan is usually a bigger box, and a bigger box is a bigger hole with drywall to patch: $662. A first installation is all of that plus a duct to the outside and a switch: $1,043 with an attic, $1,262 without.
| Job | Hours | Drywall | Fitted |
|---|---|---|---|
| Motor and grille in the old housing (handyman) | 0.5 | — | $266 |
| New fan, same-size opening | 1.5 | — | $446 |
| New fan, larger opening | 2.2 | $150 | $662 |
| First installation — no fan there | 5.2 | $150 | $1,043 |
Same 1-sone fan, same duct, attic above. The fan is $143 on every row.
Before anyone goes up a ladder
- Read the label inside the grille. Brand and model decide whether a retrofit motor exists, and that is the difference between fifteen minutes and a new hole.
- Follow the duct to where it comes out. If it does not come out, that is the job.
- Measure the run and count the elbows. It decides the fan, not the room.
- Buy the quiet one. A 4-sone fan is the one nobody turns on.
- Buy the timer switch with it. Twenty minutes after the shower is where the moisture is.
- Insulate the duct in the attic, or the steam condenses inside it and drips back through the grille in winter.
- Two bathrooms on one visit. The trip charge is most of a small job.
MaterialsEstimator, Bathroom exhaust fan replacement and installation price survey · checked 2026-09-23
What goes wrong
01Venting into the attic
Illegal, and the black stain on the roof sheathing above the bathroom is the wood rotting from shower steam.
Instead — A duct to a roof or wall cap. About $257 with the fan, and it is the installation, not an extra.
02Buying the CFM the rule names
The box is rated with no duct. On 52 equivalent feet a 50 CFM fan delivers 33, and the mirror never clears.
Instead — The first catalogue size whose derated airflow meets the room: the 80 here.
03A 4 in flex duct sagging 30 ft to the gable
Three elbows and the sag: 85 equivalent feet, and the fan delivers half.
Instead — Shorten, straighten, rigid where possible, and 6 in duct if the fan is over 80 CFM.
04A roof cap sealed on top of the shingles
It leaks within two winters, into the ceiling below, and the fan gets the blame.
Instead — Flashed like a shingle: under the course above, over the course below.
05The 4-sone builder fan
Nobody switches it on, and a fan that is off moves nothing.
Instead — A 1-sone fan, $70 more, and a switch that runs it after you leave.
06Cutting a bigger hole when a retrofit motor exists
It turns a $266 job into a $662 one with a second visit for the drywall.
Instead — Read the label inside the grille first.
07Uninsulated duct through a cold attic
The steam condenses inside the duct and runs back to drip through the grille on winter mornings — which looks like a roof leak and is not.
Instead — Insulated flex or wrapped rigid, sloped slightly towards the outside.
08Cloth duct tape on the joints
It dries out and falls off in a couple of years, and the joint leaks steam into the attic.
Instead — Clamps and foil tape. The word 'duct' on the cloth kind is a historical accident.
- 01Size the roomOne CFM per square foot, 50 minimum. Over 100 sq ft, count 50 per toilet, shower or tub and 100 per jetted tub. Tall ceilings: by volume, eight air changes an hour.
- 02Follow the ductLength, elbows, size and where it comes out. If it comes out in the attic, that is the first thing to fix.
- 03Work out what the duct costs the fanDuct feet plus 15 per elbow plus 10 for the cap. On a 4 in duct, past 25 equivalent feet the fan loses a fifth; past 50, a third; past 75, half.
- 04Buy the fan that delivers, not the fan the rule namesThe first catalogue size whose derated airflow meets the room's number. Usually one or two sizes up.
- 05Read the label inside the grilleIf the brand makes a retrofit motor for that housing, the job is fifteen minutes from below.
- 06Change the switchA timer or humidity sensor is the cheapest thing that changes how the bathroom smells.
A ceiling fan is the same electrician, the same trip charge, and a box in the ceiling that has to be rated for it — worth booking on the same visit.
The other fan in the house- CFM
- Cubic feet per minute of air the fan moves. The number on the box is measured at 0.1 in of static pressure — almost no duct — and a real duct takes a large share of it.
- Sone
- A loudness unit. One sone is a quiet refrigerator; four is a fan everybody hears. Quiet fans get used, and a fan that is used is the one that works.
- Static pressure
- The resistance the duct puts up against the fan. Every foot of duct, every elbow and the cap add to it, and the fan's airflow falls as it rises.
- Equivalent length
- Straight duct plus 15 ft for every elbow and 10 ft for the cap. The single number that says how much of the rated CFM will get outside.
- Retrofit motor
- A replacement motor, blower and grille that drops into a brand's existing housing. Fifteen minutes from below, no attic, no drywall.
- Housing
- The metal box in the ceiling that the motor sits in and the duct attaches to. Quieter and stronger fans usually come in larger housings, which means a larger hole.
- Roof cap
- The hooded, dampered outlet through the roof, flashed under the shingles above and over the ones below. The shortest route out of most bathrooms and the one that leaks when it is done badly.
- Wall or gable cap
- A hooded outlet through the siding. Nothing to leak, usually a longer run — and a longer run is a weaker fan.
- Soffit cap
- An outlet in the eave. Fine when it blows outward through a proper cap; not fine when it blows into the soffit cavity, which is the attic by another door.
- Backdraft damper
- The flap in the fan or the cap that stops cold air coming back in. Two of them, one at each end, is right; none is a draught in winter.
- Timer switch
- Push a button for 20 or 30 minutes and walk away. The fan runs after the shower, which is when the moisture is.
- Humidity-sensing switch
- Turns the fan on when the shower raises the humidity and off when it drops. It takes the person out of the system.
Common questions
- How much does it cost to replace a bathroom exhaust fan?
- About $446 for a new 1-sone fan in the same-size opening, fitted by an electrician — $143 of fan, 1.5 hours and a $160 trip charge. If the brand sells a retrofit motor for the old housing, a handyman does it from below for about $266. A quieter fan that needs a bigger hole is about $662 with the ceiling patched.
- How much does it cost to install a bathroom exhaust fan where there is none?
- About $1,043 with an attic above — an opening cut, the housing on a joist, 12 ft of duct to a roof cap, a switch wired from the light, and the ceiling patched. Without an attic, with the duct fished to a wall cap, about $1,262. The duct and the cap are not extras; they are the installation.
- What size bathroom exhaust fan do I need?
- By the rule, one CFM per square foot with a 50 CFM minimum, so a 40 sq ft bathroom needs 50. But the box is rated at almost no resistance, and 12 ft of 4 in duct with two elbows and a roof cap is 52 equivalent feet, on which a fan delivers about 65 per cent of its rating. A 50 CFM fan on that duct delivers 33. The fan to buy is the 80 — the first catalogue size that gets 50 outside. Over 100 sq ft, the rule counts fixtures instead: 50 each, 100 for a jetted tub, so a large bathroom with a jetted tub needs 200.
- Why does my new bathroom fan not clear the mirror?
- Almost always the duct. A 4 in flexible duct that sags, runs 30 ft to the gable and turns three corners is 85 equivalent feet, and the fan delivers half of what the box says: a 50 CFM fan gives 25. The fixes, in order of cost: shorten and straighten the run, replace flex with rigid, go to 6 in duct — on which the same room needs only a 70 CFM fan — or buy a bigger fan.
- Can a bathroom fan vent into the attic?
- No. The residential code requires exhaust to discharge outdoors, and the reason is visible in any attic where it does not: shower steam condensing on the underside of the roof deck every morning, the sheathing black and soft above the bathroom. Fixing it is the duct and the cap the fan should have had — about $703 with a new fan against $446 for the fan alone.
- Should the fan vent through the roof or the wall?
- The roof is the shortest run from most bathrooms and the one that leaks: the cap goes under the shingles above and over the ones below, like a shingle, and a cap that is just sealed on top leaks in two winters. A wall or gable cap has nothing to leak but usually a longer run, and a longer run is a weaker fan. The soffit is fine only with a proper cap that blows outward — into the soffit cavity is the attic by another door.
- What is a retrofit motor, and can I use one?
- A replacement motor, blower and grille that drops into a brand's existing housing from below — no attic, no drywall, fifteen minutes. Most big brands make them for their common housings. Read the label inside the grille: if the brand matches, it is the $266 job instead of the $446 one, and the new motor's noise and airflow come with it.
- How many sones should a bathroom fan be?
- One or less, if it is a fan that is meant to run. A 4-sone builder fan is the one nobody switches on, and a fan that is not switched on moves nothing. The quiet fan is $70 more, and on a $446 job it is the part worth paying for.
- Should I get a timer or humidity switch?
- Yes — it is the cheapest thing on this page that changes how the bathroom smells. On the light switch the fan runs while you are in the room and stops when you leave, which is when the moisture is. A timer is $30 and runs 20 minutes after; a humidity sensor is $48 and does it without anybody pressing anything.
- Can I replace a bathroom exhaust fan myself?
- A motor swap or a same-size replacement, yes: about $173 of fan and a timer switch. Breaker off, the old housing out, the new one screwed to a joist, the duct clamped and foil-taped, the wiring reconnected under the cover. A new duct run to a roof cap is a roofing detail and the one to think about; venting into the attic to save the trouble is the mistake this page exists to stop.
- Does a bathroom fan need its own circuit?
- An ordinary fan or a fan-light does not; it is usually fed from the light's box. A fan with a heater does — 1,300 to 1,500 watts on its own 20 A circuit — and that is an electrician and a run from the panel, which the calculator does not include.
- How long does a bathroom fan last?
- Ten to fifteen years for the motor, and the duct outlives it. When the motor goes, a retrofit kit for the same housing is the cheap route; when the fan was never right for the room, it is the moment to change the housing and, if it vents into the attic, the duct.
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About the author
Pablo Ruiz Quintero — Editor
Editor of MaterialsEstimator. Decides which documents count as a source, what every default value is, and where the line sits between what the reader parses and what the engines compute.
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