How to Price Kitchen Extractor Hood Ducting: Labour, Materials and Margin Guide

Summary

Ducting is the part of a kitchen extraction job that's easiest to underprice, because the hood itself is usually supplied and fixed by the kitchen fitter, leaving the ducting run as an afterthought priced by eye rather than by measurement. In practice, the duct route is where compliance and performance actually live or die: a hood rated at 30 l/s on the box can deliver a fraction of that once it's connected to 6 metres of flexible corrugated duct with three 90° bends squeezed through a cupboard and a loft space.

The pricing logic for ducting has three variables that matter far more than the hood's retail price: total equivalent duct length (straight runs plus the friction penalty of every bend), duct diameter and type (rigid aluminium vs semi-rigid vs flexible), and the building fabric it has to pass through (stud wall, masonry core-drill, joisted floor, roof penetration). Get these three right in the quote and the job protects its margin; guess at them and either the customer gets an underperforming extraction system or the tradesperson eats a day's unplanned labour on a difficult route.

This guide breaks ducting pricing down by run type, gives material and labour rates, and provides worked examples for the routes that come up most often: straight wall runs, loft/joist runs to a soffit, and island hood installations where there's no nearby external wall at all.

Key Facts

• Minimum extract rate — cooker hood — 30 l/s (108 m³/h) per Approved Document F (2021); an extract point positioned elsewhere in the kitchen (not adjacent to the hob, without a hood) needs a minimum 60 l/s (216 m³/h)
• Standard duct diameter — 125mm for most residential hoods and runs up to around 3m equivalent length; 150mm for longer runs or higher-output hoods
• Every 90° bend ≈ 1m of straight duct — for equivalent length calculations; two bends on a 3m straight run gives roughly 5m equivalent length
• Rigid aluminium duct (round) — £8–£18/m supplied; best airflow performance, standard for straight or lightly-bent runs
• Semi-rigid aluminium duct — £10–£22/m supplied; flexes around minor obstructions with less performance penalty than fully flexible duct
• Flexible corrugated duct — £4–£10/m supplied; cheapest but carries a significant friction penalty — use only for short connector sections (under 0.5m), never as a full run
• Rectangular duct (flat channel) — £12–£25/m supplied; used where duct must fit within a shallow ceiling void or behind a cupboard, higher resistance than round duct of equivalent cross-section
• External wall vent/terminal (with back-draught shutter) — £15–£45 supplied
• Roof cowl/terminal (for island/vertical runs) — £40–£120 supplied, plus flashing and weatherproofing detail
• Core drill through masonry cavity wall (125–150mm) — £60–£150 labour depending on wall thickness and access, more for stone or reinforced concrete
• Fire-stopping collar — required where duct passes through a fire-rated floor or wall — £15–£40 per penetration, plus intumescent sealant
• Insulated duct sleeve/wrap — needed where duct passes through a cold, unheated void (loft) to prevent condensation dripping back into the kitchen — £6–£15/m
• Labourer/fitter day rate for ducting work — £180–£280 regional, £240–£360 London
• Productivity — straight wall run — 1–3 hours including core drill and terminal fitting
• Productivity — loft/joist run to soffit or roof — half day to a full day depending on access and roof penetration complexity
• Productivity — island hood full route — often a full day, sometimes two, particularly where floor routing for a downdraft extractor is involved
• VAT — 20% standard rate on labour and materials for most domestic ducting work

Quick Reference Table

Detailed Guidance

Building the Price: Equivalent Length First

Before pricing anything, measure the actual route the duct will take and convert it to equivalent length: straight metres plus roughly 1 additional metre for every 90° bend. A hood positioned against an external wall with a straight punch-through might genuinely be 0.5m of duct — the cheapest and fastest job in this guide. The same hood on an internal wall, routed through a cupboard, up into a void, along 4m of joist space and out through a soffit vent with three bends along the way, can easily reach 7–8m equivalent length even though the hood-to-terminal distance "as the crow flies" looks similar on a floor plan.

This matters because performance drops with equivalent length, and manufacturers publish maximum recommended run lengths for their hoods — exceed it and the customer gets a hood that never properly clears steam and grease, regardless of how well it was fitted. Price the route, not the hood.

Duct Diameter and Type Selection

125mm rigid duct is the default for runs up to around 3m equivalent length on a standard domestic hood. Beyond that, or on higher-output hoods (large canopy hoods, commercial-style extraction), step up to 150mm — the larger cross-section reduces the velocity and friction loss per metre, recovering some of the performance lost to a longer run.

Rigid round duct gives the best airflow performance for the cost and should be the default wherever the void allows it. Rectangular duct is a compromise used where ceiling or cupboard depth won't accommodate a round duct — it has more internal friction for the same cross-sectional area, so where a choice exists, round wins. Flexible corrugated duct should be priced and used only for short connector sections joining the hood outlet to the start of the rigid run, or for the final short section into a terminal — specifying it for a full multi-metre run is a common source of underperforming installations and comes up repeatedly in customer complaints about "the hood doesn't do anything."

Core Drilling and Wall Penetrations

Where the duct exits through an external wall, the core drill is priced separately from the duct itself. A single-leaf timber-frame or blockwork wall is straightforward — 1–2 hours including making good and fitting the terminal. A full cavity wall, especially with cavity wall insulation that needs a sleeve to prevent cold bridging and condensation tracking, takes longer and needs a proper insulated sleeve detail through the cavity, not just a bare pipe punched through. Stone, reinforced concrete, or particularly thick masonry can add significant time and may require specialist core-drilling equipment rather than a standard SDS setup — price this as a day-rate risk item on older or solid-wall properties rather than guessing at a fixed price.

Loft and Joist Runs

Routing duct through a loft space or between joists to reach a soffit vent or gable end is the most common "hidden cost" scenario in kitchen extraction jobs, because the route often isn't visible or fully understood until the fitter is up in the loft. Key pricing considerations:

• Insulation and condensation — duct passing through an unheated loft must be insulated (sleeve or wrap) to stop warm, moist kitchen air condensing inside the cold duct and dripping back into the kitchen; this is a real, common defect on unpriced/rushed jobs
• Fall towards the terminal — the duct should have a slight fall towards the external end so any condensate that does form runs out rather than back into the kitchen
• Joist notching/drilling — where the duct must cross joists rather than run parallel to them, notching or drilling within Building Regulations structural limits takes time and may need to avoid services already in the void
• Access — a boarded, well-lit loft with easy hatch access is a different job to a cramped, part-insulated loft with restricted headroom; price access difficulty explicitly rather than assuming a standard rate

Island Hoods and Downdraft Extractors

Island and downdraft installations are the highest-value, highest-risk ducting jobs because there's no nearby external wall to exploit — the duct must route through the ceiling void to a roof penetration, or below the floor to an external wall at floor level. These routes are very difficult to retrofit cleanly once a kitchen is fitted, so pricing should include:

• Full route survey before the kitchen units go in, wherever possible — retrofitting island extraction after installation multiplies the labour significantly
• Roof cowl and flashing detail if routing to a roof penetration, priced as a distinct line item alongside any roofer/roofing subcontractor needed for the weatherproofing
• Fire-stopping collars at every fire-rated floor or ceiling penetration
• A realistic day-rate allowance rather than a fixed price — island/downdraft routing has the widest variance of any ducting scenario in this guide, and quoting it as a fixed low price is a common margin killer

Where Ducting Jobs Lose Money

• Underestimating equivalent length — pricing by the straight-line distance on a floor plan rather than the actual routed path including bends
• Specifying flexible duct for a full run to save on materials — the performance shortfall becomes the tradesperson's problem when the customer complains, not a material cost saving
• No allowance for core drilling difficulty — solid or reinforced walls take multiples of the time of a stud or single-skin blockwork wall
• Missing the insulation/condensation detail on cold-void runs — a callback for dripping condensate costs far more than the £6–£15/m insulated sleeve would have
• Treating island/downdraft routing as a standard job — these routes have genuinely higher variance and need day-rate or surveyed pricing, not a flat quote from a floor plan alone

Frequently Asked Questions

Does a recirculation (ductless) hood avoid all of this pricing complexity?

Yes for ducting cost, but it comes with a compliance caveat: recirculation hoods with charcoal filters remove grease and odour but don't achieve the ventilation function required by Approved Document F, because moisture-laden air is returned to the kitchen rather than removed. They're a legitimate practical solution where duct routing genuinely isn't feasible (internal kitchens in flats, listed buildings), but the compliance position should be discussed with the customer rather than defaulted to purely to avoid ducting cost — see kitchen extract for the full Part F position.

How much extra should I charge for a bend versus a straight run?

Price bends as roughly equivalent to an extra metre of straight duct each, both in material cost (fittings) and in labour time (each bend typically needs more careful jointing and support). A route with two bends and 3m of straight duct should be priced closer to a 5m equivalent-length job than a 3m one.

Is it worth quoting a fixed price for island hood ducting?

Generally no, unless you've physically surveyed the route before the kitchen units are installed. Island and downdraft routing has the widest cost variance in kitchen extraction work — a day-rate-with-estimate approach, clearly communicated to the customer up front, protects margin far better than a fixed price guessed from a kitchen design drawing.

What's the single biggest cause of underperforming kitchen extraction after installation?

Excessive equivalent duct length combined with undersized or flexible ducting for the run length — a hood that's rated correctly on the box but connected via 6–8m of flexible corrugated duct with multiple bends will underperform badly regardless of installation quality elsewhere. Pricing (and specifying) the duct route properly at quote stage is what prevents this.

Regulations & Standards

• Building Regulations Approved Document F: Means of Ventilation (2021) — minimum extract rates (30 l/s for cooker hoods, 60 l/s for a non-hob-adjacent extract point) and the requirement that ducted extraction discharge to outside

• Building Regulations Approved Document J: Combustion Appliances — clearance and air supply considerations where hoods are fitted above gas hobs

• Gas Safety (Installation and Use) Regulations 1998 — minimum clearance from gas hobs to combustible materials, including hood height above the hob

• BS EN 61591 — domestic cooking fume extractors; test methods and performance classification referenced by hood manufacturers

• Building Regulations Approved Document B — fire-stopping requirements where ducts pass through fire-rated floors, walls or ceilings

• MHCLG: Approved Document F 2021 — full ventilation rate and compliance requirements

• BEAMA Kitchen Ventilation Guidance — industry guidance on Part F compliance for kitchen extraction

• Gas Safe Register — Cooker Hood Installation — gas hob clearance requirements

• kitchen extract — Part F compliance detail, hood height and duct sizing reference

• extractor fan installation pricing guide — pricing for the fan/hood unit and electrical connection, complementary to ducting-specific pricing here

• part f ventilation — the four ventilation strategies and extract rate requirements in full

• extractor fan — fault diagnosis for underperforming or non-functioning extraction after installation