Most bathroom fan problems I see on survey aren't a dead fan — they're the right fan in the wrong job. A 100mm wall-mounted fan, the kind covered in my bathroom extractor fan guide, is built to push air straight through a wall or a short length of ducting to the outside. Ask it to clear a windowless ensuite three rooms deep, or serve a bathroom and a separate WC off one shared run, and it simply can't hold enough pressure over the distance and bends involved. That's the job an inline fan is built for: mounted mid-duct, usually in a loft or ceiling void, pulling air from one or more rooms through a longer run to a single outlet.
The distinction that actually matters when buying one is mixed-flow versus axial. An axial fan — a simple propeller in a tube — loses static pressure fast once it's fighting distance, bends or a grille at the far end; it's fine for a short, straight hop and struggles beyond that. A mixed-flow (sometimes called centrifugal) fan uses an impeller design that holds pressure over a genuinely long run, which is the whole reason this category of fan exists. Get that wrong and you've bought an inline fan that behaves like an underpowered wall fan.
An inline fan isn't the answer to every damp bathroom, though. If condensation and mould are turning up well beyond the room the fan serves — landing ceilings, bedroom corners, wardrobes on external walls — that's a whole-house ventilation question, and a PIV unit or a proper look at MVHR installation costs is the more honest fix than swapping one room's fan. And where the duct run to an external wall is short and straight, a standard wall-mounted fan is simpler, cheaper and easier to service — don't buy an inline fan for a job a wall fan already does well. With that sorted, here are the six I'd look at.
The one I’d buy
Envirovent Silent MV 160/100T
This is a genuine mixed-vane (MV) inline fan, sound-insulated so it doesn't turn a loft void into a low hum you can hear downstairs. The two-speed switch gives 50 l/s on high — real headroom over the 15 l/s Part F minimum — and 38 l/s on a quieter low setting, with an adjustable overrun timer to clear the air after use.
Typically £60–£75
Check price on AmazonHow I judge an inline extractor fan
Mixed-flow versus axial — the fork that decides everything else. A mixed-flow (centrifugal) fan holds static pressure over a long run of ducting; an axial fan is a propeller in a tube that loses pressure fast beyond a short, straight hop. Check which type you're actually buying before comparing prices — some budget "inline" fans are axial units in inline housings.
Duct diameter and total run against real static pressure, not the headline rate. Every extract-rate figure on a spec sheet is measured free-air, with nothing attached. Wire the same fan into 5m of ducting with a couple of 90° bends and the number it actually delivers drops — a rate with real headroom above the Part F minimum matters more than one that only just clears it on paper.
Where it physically sits. An inline fan lives mid-duct, in a loft or ceiling void, which means it needs to be reachable for cleaning and eventual replacement. A fan boxed in behind a fixed ceiling with no hatch nearby is a problem for whoever has to service it in five years' time.
Control that matches the room. A timer suits predictable use; a humidistat responds to actual moisture whenever it rises, which matters more in a room used outside a routine. Several fans here are timer-only, which is where a standalone humidistat controller earns its place.
Noise quoted honestly. A dB(A) figure at a stated distance and speed is useful; a "quiet" claim with no figure or measurement point behind it isn't worth much when the fan is sitting above a bedroom ceiling.
The comparison
| Model | Type | Duct | Extract rate | Typical price | Best for | |
|---|---|---|---|---|---|---|
| Envirovent Silent MV 160/100T | Mixed-flow | 100mm | 50 l/s | ~£60–£75 | Best all-round pick | View |
| Vent-Axia ACM100T | Mixed-flow | 100mm | Timer-controlled | ~£140–£165 | Trade-grade build | View |
| Blauberg Turbo 150 | Mixed-flow | 150mm | ~350 m³/h | ~£75–£95 | Bigger or multi-room jobs | View |
| Manrose MF100T | Mixed-flow | 100mm | 68 l/s | ~£55–£70 | Well-known trade brand | View |
| Manrose MAN1361 | Humidistat controller | — | 20–90% RH threshold | ~£45–£55 | Adding humidistat control | View |
| Blauberg Tubo-U-100T | Axial | 100mm | ~102 m³/h | ~£28–£38 | Short, straight run only | View |
The picks in detail
Envirovent Silent MV 160/100T
Best all-round — genuine mixed-flow performance with real headroom over Part F
The MV in the name stands for mixed vane, and it's a proper mixed-flow design rather than an axial fan in inline housing, which is what actually lets it hold pressure over a long duct run. The sound-insulated casing keeps it quiet enough not to be noticed from the room below, 50 l/s on the high speed setting gives genuine headroom above the 15 l/s Part F minimum, and the overrun timer is adjustable between 2 and 25 minutes to clear the air properly after use.
For
- Genuine mixed-flow design holds pressure over a long run
- 50 l/s high speed gives real headroom over the Part F minimum
- Sound-insulated casing for a quieter loft void
Against
- Timer only — no humidistat sensor built in
- Needs three wires at the switch for the timer to work
Typically £60–£75
Check price on AmazonVent-Axia ACM100T
Best trade-grade build — for a job that needs to outlast a cheap plastic housing
Vent-Axia is a name most electricians already trust, and the ACM100T carries that trade reputation into a mixed-flow inline unit built for continuous mid-duct duty, with an adjustable overrun timer. Worth flagging honestly: the Amazon listing itself publishes almost no spec beyond the product name, so I'd check Vent-Axia's own datasheet for the exact airflow and noise figures before speccing a specific job, rather than relying on the listing alone. It's also priced roughly double the other 100mm fans here.
For
- Recognised trade name with a track record in boxed-in installations
- Robust housing built for continuous duty
- Adjustable overrun timer
Against
- Roughly double the price of the other 100mm fans here
- The Amazon listing is thin on published spec — check Vent-Axia's own datasheet first
Typically £140–£165
Check price on AmazonBlauberg Turbo 150
Best for a bigger job — 150mm duct for a multi-room or high-output run
Step up to a 150mm duct and this mixed-flow fan gives the headroom a 100mm unit can't: a large ensuite with a powerful shower, or one duct system serving a bathroom and a separate WC together. Part F allows a single extract system to serve more than one wet room provided the combined rates and duct sizing add up for every room served — this is the fan built for that job. One honest caveat: Blauberg sells several Turbo 150 submodels with different noise and airflow figures, and the Amazon listing doesn't specify which is sold, so treat the quoted spec as approximate and confirm the exact datasheet before fitting.
For
- 150mm duct gives real headroom for a bigger or multi-room job
- Part F allows one system to serve several wet rooms if sized correctly
Against
- Several Turbo 150 submodels exist with different specs — confirm the exact datasheet before fitting
- Pricier than the 100mm options here
Typically £75–£95
Check price on AmazonManrose MF100T
Best well-known trade brand — strong headroom at a fair price
MF stands for mixed flow, and this is Manrose's mainstream inline offering: 68 l/s on high and 50 l/s on low, both well clear of the Part F minimum, with an adjustable overrun timer and the kind of name most builders' merchants stock parts for. One thing worth knowing before you buy: Manrose's own spec is explicit that this exact model is not humidistat-compatible. If you want that control from the outset, either buy the humidistat-compatible MF100S sibling instead, or add pick 05's remote controller to this one.
For
- 68 l/s high speed gives strong headroom over Part F
- Well-known trade brand, easy to source replacement parts
Against
- Not humidistat-compatible on this exact model — see pick 05, or buy the MF100S sibling instead
Typically £55–£70
Check price on AmazonManrose MAN1361 Remote Humidistat
Best way to add humidistat control to almost any fan
This isn't a fan — it's a wall-mounted controller that retrofits humidistat and timer control onto a fan that doesn't have a sensor built in, including several of the timer-only picks above. The humidity threshold is adjustable across 20–90% RH, so it can be tuned to stop a naturally steamy room short-cycling, and the overrun timer runs 1–60 minutes. It fits a standard single-gang back box and handles loads up to 200W, which covers every fan in this guide.
For
- Turns almost any timer-only inline fan into a humidity-responsive one
- Adjustable RH threshold tunes out short-cycling
- Fits a standard single-gang back box
Against
- Needs a three-wire supply reaching the fan, same as any humidistat control
- An added cost and install step on top of the fan itself
Typically £45–£55
Check price on AmazonBlauberg Tubo-U-100T
Cheapest — but only for a genuinely short, straight run
This is an axial fan in inline housing, not the mixed-flow design the rest of this guide is built around, and it's worth being upfront about what that means: Blauberg's own literature rates it for runs up to around 3m, and static pressure drops off fast beyond that or through more than a couple of bends. Bought for the right job — a short, straight hop through a loft void — it comes with a mounting bracket and timer included at the cheapest price on this list. Bought for a long run, it won't clear the room properly.
For
- Cheapest fan here, mounting bracket and timer included
- Fine for a short, straight run
Against
- Axial design, not mixed-flow — performance drops off fast over distance or bends
- Airflow and noise figures for this one are less well corroborated than the others here — check the current listing before buying
Typically £28–£38
Check price on AmazonWhat actually matters — and what doesn’t
Mixed-flow versus axial is the real fork in the road, not price or brand. A mixed-flow fan is built to hold static pressure over a long duct run; an axial fan loses it quickly beyond a short, straight hop. Check which type is actually inside the housing before comparing anything else — the word "inline" on the box doesn't tell you which one you're getting.
The spec-sheet extract rate is measured free-air, not through your actual ducting. Every figure in the comparison table above is a best-case number with nothing attached. Wire the same fan into a real run with bends, a grille and a length of flexible ducting, and what it actually delivers is lower — buy headroom over the Part F minimum, not a number that only just scrapes it.
Where it sits has to be reachable. An inline fan lives mid-duct, almost always in a loft or ceiling void. If there's no hatch or access panel nearby, whoever eventually has to clean or replace it is in for a difficult afternoon — plan the mounting position around future access, not just the shortest run.
Humidistat, timer and PIR measure different things. A timer runs for a fixed period after being triggered by a switch — simple, but blind to actual humidity. A humidistat reacts directly to rising moisture, which is why Part F guidance favours it for windowless rooms and spaces with unpredictable use. A PIR sensor reacts to movement, not moisture, which suits general air freshness better than condensation control — don't assume the two are interchangeable.
One fan can legally serve more than one room — if the sizing adds up. Part F permits a single extract system to serve several wet rooms (an ensuite and a separate WC, say) provided the combined extract rates for every room served are met and the ducting is sized for the total load. That's a proper calculation, not just physically connecting two grilles to one duct.
What gets pushed that matters less than it sounds. A maximum free-air airflow figure isn't what the fan delivers day to day through real ducting, and a bigger duct diameter isn't automatically better if the room's actual extract requirement doesn't need it. Real headroom on a realistic, ducted extract rate beats any single headline number.
Questions I get asked
What's the actual difference between an inline fan and a normal bathroom fan? A standard bathroom fan mounts through the wall or ceiling and pushes air a short, direct distance outside. An inline fan sits mid-duct, usually in a loft or ceiling void, and is built to hold pressure over a longer run with bends — the job a wall fan can't do.
Do I need Building Control sign-off to fit an inline fan? Replacing an existing fan like-for-like on its existing ducting and cabling generally doesn't need notifying. Adding a new duct run, cutting a new external outlet, or converting a passive vent into a powered system is more likely to raise a question — ask whoever fits it to confirm.
Can one inline fan serve two rooms, like an ensuite and a separate WC? Yes, provided the combined extract rates for both rooms are met and the ducting is sized for the total airflow — that calculation is the installer's job, not something to assume from the fan's spec sheet alone.
Will fitting a humidistat make the fan run constantly? No — it only switches on once relative humidity crosses the threshold you set, then runs an overrun period once it drops back down. A naturally steamy bathroom running near-constantly usually means the threshold needs adjusting, not that the humidistat itself is faulty.
I don’t install ventilation systems myself, but a ventilation testing visit shows what an existing inline fan actually delivers against what Part F expects, and a PAS 2035 retrofit assessment is the right next step if condensation is spreading well beyond one room — that's usually a PIV unit or a proper look at MVHR installation costs, not a fan swap. Where the duct run is short and straight, a standard wall-mounted fan is the simpler and cheaper answer. Get in touch for a second opinion, and there are more field-kit guides to work through.
Small print. This guide is general information, not a recommendation on whether your specific installation needs an inline fan or a different ventilation strategy — get that diagnosed properly first, and have the electrical connection and duct sizing carried out by a competent installer. Prices are indicative, move constantly and are checked at the time of writing; the linked page always shows the current price. As an Amazon Associate I earn from qualifying purchases.