Summary
Extractor fan installation looks like a quick "fit and forget" job — most tradespeople price it the way they price changing a light fitting, then lose money. The reality is that a modern compliant installation includes a building-regs ventilation calculation, a core-drilled external penetration, properly sealed ducting (insulated where it crosses a cold zone), an electrical termination that meets Part P in a bathroom, and commissioning to demonstrate the airflow on completion. Each of those items has a real cost.
The price spread between a budget swap-out and a fully compliant new install is large — sometimes £150 vs £750 for what the customer sees as the same job. Tradespeople who price by gut feel and don't itemise lose either jobs (priced too high) or money (priced too low). The pricing logic in this article gives you a defensible breakdown you can talk through with the customer at the door: ventilation rate required, duct route, fan type, electrical, commissioning. Everything else is fluff.
The market also splits sharply by who is doing the work. Bathroom fan swaps are typically done by electricians (Part P territory, low complexity). New extraction through a wall, kitchen hood ducting, and any MVHR-adjacent work involves carpentry, masonry (core drilling) and ventilation knowledge — these are higher-value jobs and the customer is usually shopping on outcomes (noise level, condensation gone, smell gone) rather than headline price.
Key Facts
- Ventilation rate (Approved Document F) — Kitchen 30 l/s (cooker hood) or 60 l/s elsewhere; Utility 30 l/s; Bathroom 15 l/s; WC 6 l/s — intermittent extract
- Continuous extract alternative — 13 l/s kitchen, 8 l/s utility, 8 l/s bathroom, 6 l/s WC (background rate, runs constantly)
- Notifiable to Building Control — A new extract fan is generally NOT notifiable on its own, but the associated electrical work in bathroom Zones 0–2 IS notifiable under Part P
- Part P (electrical) — Bathroom extract wiring inside the bathroom is notifiable; the fused spur in an adjacent room is not. New circuits anywhere are notifiable
- Typical fan power draw — 6–25W intermittent axial; 5–15W centrifugal in-line; 8–40W continuous mechanical extract
- Run-on timer — Required in any room without an openable window (Approved Document F); typically 15-minute overrun after light switch off
- Duct diameter — 100mm for axial fans, 125mm for in-line centrifugal, 150mm for kitchen hoods; never reduce duct downstream
- Duct condensation control — Cold-zone ducting (loft, external) must be insulated to BS 5422; flexible plastic ducting NOT acceptable in cold zones for kitchen extract per Approved Document F guidance
- Backdraught shutter — Required at the external termination; some fans include integral shutter, otherwise external grille with non-return flap
- External termination distance — Minimum 1m from opening windows, 2m from a combustion appliance flue, 600mm above ground
- Commissioning — Approved Document F requires airflow measurement at handover; a vane anemometer reading is the simplest evidence
- Typical labour time — Like-for-like swap: 1.5–2.5 hours; new wall fan: 3–5 hours; kitchen ducted hood: 5–8 hours; in-line ceiling extract: 4–6 hours
Quick Reference Table
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Try squote free →| Job Type | Materials Typical | Labour Hours | Typical Customer Price |
|---|---|---|---|
| Bathroom axial fan, like-for-like swap | £35–£90 | 1.5–2.5 | £120–£250 |
| Bathroom axial fan, new install | £45–£120 | 3–5 | £250–£500 |
| Bathroom in-line centrifugal (quieter) | £150–£300 | 4–6 | £400–£700 |
| Kitchen recirculation → ducted conversion (short run) | £150–£300 | 5–8 | £450–£800 |
| Kitchen recirculation → ducted conversion (long run, soffit) | £200–£450 | 8–14 | £700–£1,200 |
| Roof-mounted in-line fan with cowl | £300–£600 | 6–10 | £700–£1,200 |
| Whole-flat continuous extract (MEV) | £600–£1,500 | 12–20 | £1,800–£3,500 |
| Cost Component | Typical Cost (Trade) | Notes |
|---|---|---|
| Axial fan (basic timer) | £25–£60 | Vent-Axia, Manrose, Xpelair |
| Quiet axial fan | £50–£120 | Envirovent Silent, Vent-Axia Lo-Carbon |
| In-line centrifugal | £80–£180 | Higher static pressure, longer runs |
| Humidity sensor model | £45–£100 | Add £20–£30 over plain timer |
| 100mm rigid duct (per 1m) | £4–£8 | PVC; insulated for cold zones £8–£15 |
| External wall grille (white) | £8–£18 | Stainless or anti-bird £18–£40 |
| Core drilling (100mm masonry) | £40–£80 per hole | Includes diamond bit hire |
| Core drilling (125mm masonry) | £55–£100 per hole | |
| Fused spur (3A) | £12–£25 | Per Part P installer rates |
| Insulated flexi (per 1m) | £8–£14 | For loft/eaves cold sections |
| Variable | Effect on Price |
|---|---|
| External wall masonry vs timber-frame | Masonry adds £40–£100 (core drilling) |
| First-floor with no scaffold access | Add tower hire £40–£80 |
| Pipe boxing/MDF reinstatement | Add £80–£180 |
| Re-decoration after dust | Add £60–£200 (or noted as customer's responsibility) |
| Asbestos suspected on external wall (pre-2000 cladding) | STOP — separate survey/removal job |
| Listed building / conservation area | Add survey and possible HE/LPA notification |
Detailed Guidance
Pricing Logic
Build the price from five components, in this order:
- Compliance baseline — what airflow rate does Approved Document F require for the room? This dictates fan type and minimum capacity. Don't allow the customer to spec a "quiet but underpowered" fan that won't meet the regs.
- Duct route — measure it. Short straight runs through a single-leaf external wall are cheap; long runs through a loft to a soffit or up through a roof are 3–5× the time and twice the materials.
- Electrical — is there an existing supply in compliance with Part P? In a bathroom, can the existing isolator be reused? New 3A fused spur in an adjacent room is straightforward; a new circuit back to the CU is a different job.
- Reinstatement — making good plaster, tiles, kitchen units, paintwork. This is where unmarked jobs lose money. Decide upfront whose responsibility this is and itemise it.
- Commissioning and certification — airflow check, customer hand-over, Part P certificate where applicable. This is 30 minutes of time that always seems "free" but is real labour.
Add a contingency for surprises (asbestos in soffit boards, hidden cable runs, structural lintel in the way of the core drill). 10–15% on a routine job, 25% on anything in a building older than 1980.
Bathroom Fans: The Common Job
The default UK bathroom fan job is a 100mm axial fan ducted through an external wall, with a 3-minute run-on timer, on a fused spur off the lighting circuit.
A like-for-like swap (existing fan, existing duct, existing wiring) is 1.5–2 hours: isolate, remove old fan, fit new fan, test, refit grille. £120–£250 customer price is reasonable; if you're being asked to do it for £80 you're losing money once you factor in materials, vehicle, insurance and tax.
A new install adds: site survey, drilling/notifying for the spur, core drilling the external wall, fitting the duct, mounting the fan, sealing the penetration, fitting the external grille, commissioning. 3–5 hours, £250–£500 customer price.
Where the customer wants "the quiet one", the move is to an in-line centrifugal fan mounted in the loft above the bathroom — the fan motor is 2–3m away from the room so the bathroom only hears the air movement, not the motor. This adds £150–£250 in materials and 2–3 hours of labour but transforms perceived comfort. £400–£700 customer price.
Kitchen Hoods: Where Most Customers Get It Wrong
Most kitchen "extractor hoods" sold by appliance retailers are recirculating units — the air goes through a carbon filter and back into the kitchen. They remove some smell but no steam, no heat, no airborne grease over time. Approved Document F requires actual extraction for new kitchens, but does not (yet) mandate conversion of existing recirculating units in renovation work.
The conversion job is: cut the recirculation duct, route a new 125–150mm rigid duct out through an external wall (or up through the unit, into the soffit, and out through an eaves grille), seal everything, fit a backdraught shutter, commission.
The killer variable is the duct route. A hood directly against an external wall: 4–6 hours. A hob on an internal wall with a 4m duct run through three cabinets and an eaves termination: 10–14 hours. Walk the route with the customer and price it honestly. Hidden runs through cabinets always cost more than the customer expects.
When the Job Becomes a Bigger Job
Watch for these flags during the survey:
- Mould or condensation already visible — the existing ventilation is inadequate; offer the customer a continuous-extract upgrade rather than a like-for-like swap, with the cost difference clearly stated
- Pre-2000 ceiling or soffit material — possible asbestos cement; stop and survey before drilling
- Existing fan rated <8 l/s with no openable window — non-compliant; recommend a continuous-extract solution
- New build with MVHR — do not fit individual extract fans; the whole-house system is the extraction strategy and adding a wall fan creates pressure imbalance
These conversations need to happen before the quote, not after. A customer who specifically wants "the same fan I had" may push back; explain in plain terms that what they had wasn't compliant, and what compliant looks like.
Worked Example: Bathroom Fan New Install
Job: New 100mm axial humidistat fan, ducted through 215mm cavity external wall to a stainless grille; new 3A fused spur off the upstairs ring, run via a 1.5mm² T&E cable in the loft; commissioning with anemometer; final clean.
| Item | Cost |
|---|---|
| Vent-Axia Silent Identity humidistat fan | £85 |
| 1m insulated 100mm flexi duct + duct collar | £18 |
| Stainless backdraught grille | £24 |
| 5m T&E 1.5mm² + fused spur unit | £18 |
| Filler, sealant, fixings | £8 |
| Materials subtotal | £153 |
| Labour 4 hours @ £55/hr | £220 |
| Core drilling (sub or own kit, includes bit wear) | £55 |
| Commissioning, certification, clean | £35 |
| Labour subtotal | £310 |
| Subtotal | £463 |
| Markup 20% | £93 |
| Net price | £556 |
| VAT 20% (if registered) | £111 |
| Customer price | £667 |
In real markets this sits at the middle of the £400–£700 quiet-fan band. A non-VAT registered sole trader doing the same work would price around £556. Use that gap as a competitive lever, not a guilt trip — VAT-registered businesses have legitimate overheads sole traders don't.
Frequently Asked Questions
Is fitting a bathroom extract fan notifiable under Part P?
The fan itself is not notifiable, but any new electrical work inside a bathroom IS notifiable (bathrooms are special locations under Part P regardless of the new-circuit rules elsewhere). If the existing wiring already terminates inside the bathroom at the fan position, swapping the fan onto that wiring is not notifiable. If you are running new cable, fitting a new isolator inside the bathroom, or extending an existing circuit into the bathroom, it is.
What's the difference between intermittent and continuous extract?
Intermittent runs only when the room is occupied (light switch + run-on timer) and provides 15 l/s in a bathroom. Continuous extract runs 24/7 at a lower background rate (8 l/s) and boosts on humidity sensor. Continuous extract is increasingly the default in new-build and renovation because it controls condensation and air quality continuously; intermittent is the default in pre-existing installations.
Can I use flexible duct everywhere?
No. Flexible plastic duct is not acceptable for kitchen extract in cold zones (loft, external wall cavity) under Approved Document F guidance — it generates excess static pressure and is condensation-prone. Use rigid PVC or insulated rigid duct for the main run, with a short (max 1m) section of flexible at the fan connection if needed for alignment.
How do I prove the fan meets Approved Document F airflow?
A vane anemometer reading at the room grille is the standard evidence; quote the reading in your handover paperwork. The fan manufacturer's nominal airflow is a free-air figure that the duct losses will reduce in real life — only the on-site reading is meaningful. Allow 10–15% margin above the regulatory minimum.
What's the typical price for a "quiet" upgrade?
In-line centrifugal fans mounted in the loft (so the noise source is away from the room) typically add £200–£350 over a basic in-bathroom axial. Customers asked to choose between a £200 noisy fan and a £450 quiet one mostly take the quiet one if you explain why; the price difference is not the same as in the same place — it is the price of solving the problem they actually care about.
Regulations & Standards
Approved Document F (Ventilation) — Required ventilation rates for new and existing dwellings
Approved Document P (Electrical safety) — Notifiable work in bathrooms; competent persons scheme certification
BS 7671:2018+A2:2022 — Wiring Regulations (the IET Wiring Regulations / 18th Edition)
BS 5440-1:2008 — Specification for installation and maintenance of flues and ventilation for gas appliances (where extract interacts with a gas appliance)
BS 5422:2009 — Method for specifying thermal insulating materials for ducts
BS EN 13141 — Ventilation for buildings — performance testing of components/products for residential ventilation
BS EN 12237 — Ventilation for buildings — ductwork — strength and leakage of circular sheet metal ducts
HSE COSHH — When drilling into pre-2000 cement-board soffit, asbestos risk assessment may be required
Approved Document F — Building Regulations Part F
Approved Document P — Building Regulations Part P
BEAMA Ventilation Guide — Trade body technical guidance
HVCA / BESA TR/19 — Ductwork specification and cleanliness
bathroom zones — Zone classification for bathroom electrical work
extractor fan — Diagnosing existing fan faults
part f ventilation — Approved Document F deep dive
kitchen extraction and ventilation — Kitchen-specific extraction options