Inline Mixed Flow Duct Fans

Inline mixed flow duct fans — also called mixed flow extractor fans or mixed flow inline fans — combine the high airflow of an axial fan with the pressure capability of a centrifugal fan, making them the quiet, efficient workhorse of bathroom, kitchen, office and light-commercial extract. We stock mixed flow fans from 100mm to 650mm across S&P, Vent-Axia, Elta Jetflow, Manrose, Systemair and Xpelair, including silent/acoustic versions, EC models and variants with integrated timer, humidistat and run-on control. 

Inline Duct Fans / Commercial Box Fans / Bathroom Extractor Fans / MVHR Units.

What is a mixed flow fan?

A mixed flow fan (sometimes called a mixed flow extractor fan) is an inline duct fan whose impeller draws air through the fan both axially (along the shaft) and centrifugally (outward at 90°) at the same time — a mix of the two flow types, hence the name. The result is a fan that moves more air than an axial fan of the same size but handles more duct pressure than a centrifugal fan of the same size, in a compact round housing that drops straight into a standard duct run. Mixed flow fans are the default choice for bathroom extract, utility room ducting, light-commercial toilets and offices, and any job where you need quiet, efficient airflow over a moderate run of duct.

Mixed flow vs centrifugal vs axial — which one do I need?

Axial inline fans (Systemair RVK, Elta VL) move a lot of air at very low pressure — fine for short, straight, unrestricted duct runs. Centrifugal inline fans (S&P VENT-NK, Hydor HIT) hold their airflow against high static pressure — long runs, bends, filters, carbon units. Mixed flow sits in the middle: more pressure than axial, more airflow than centrifugal, quieter than both. If your duct run is under 10 metres with one or two bends and you want quiet operation, a mixed flow fan is usually the right answer. For 20m+ runs with filters or charcoal units, step up to centrifugal. For short blow-through extract, an axial is cheaper.

What's a silent mixed flow fan — and do I need one?

Silent mixed flow fans (S&P TD Silent range — TD-160/100, TD-250/100, TD-350/125 and up) have an acoustically insulated outer housing that absorbs the motor and impeller noise before it reaches the duct. Typical sound reduction is 10–15dB(A) compared to the standard TD range, which is a halving of perceived loudness. You need a silent model where the fan sits close to a ceiling grille in a bedroom, home office, meeting room, consulting room or anywhere occupants will be near the duct path. For loft or void installs with long duct runs between fan and grille, standard TD is usually quiet enough and costs significantly less.

EC or AC mixed flow fan — which should I choose?

AC is the right call for short-run, on-demand extract — domestic bathrooms, cupboards, light commercial toilets — where the fan runs in short bursts controlled by a switch or PIR. EC models (Elta Jetflow SJMF range, S&P TD EVO) use 30–50% less energy at part load, give proper 0–10V modulation from a BMS or humidistat, and are mandatory on most BREEAM projects and anything chasing a low Specific Fan Power (SFP) rating under Building Regulations Part L. If the fan runs more than a few hours a day, EC pays back within one to two years; if it's used intermittently, AC is usually fine.

Timer, humidistat and run-on — which model has what?

Models with "T" or "HT" suffixes include integrated control: Vent-Axia ACM100T and ACM125T include a timer and humidistat (fan runs when humidity rises and continues for a set overrun after bathroom use); Xpelair XIMX100T includes a timer; Manrose MF100HT includes humidistat and timer; S&P TD Silent T models include timer and boost. Standard (non-T) models are wired to an external switch, PIR or humidistat controller. If you want the control built into the fan, buy a T model; if you're wiring through a BMS, zone controller or external sensor, buy the base model and control it externally.

Vent-Axia ACM range — which model for which duct?

The Vent-Axia ACM range is the most specified mixed flow fan in UK light-commercial projects. ACM100 (or ACM100T with timer) fits 100mm duct and delivers up to 300 m³/h — right for bathrooms, single toilets and small utility rooms. ACM125 / ACM125T fits 125mm and delivers up to 328 m³/h — small offices, multi-fixture toilets. ACM150 / ACM150T fits 150mm and delivers up to 558 m³/h — larger offices, meeting rooms, multi-WC commercial. T variants add integrated timer and humidistat. All ACM fans are speed-controllable via Vent-Axia's own controller or any TRIAC/thyristor speed controller.

Brand decoder — Manrose MF, S&P TD, Elta Jetflow SJMF, Xpelair XIMX

Manrose MF (MF100S, MF125S, MF150S) is the UK-made budget mixed flow range — solid airflow figures, simple pricing, widely stocked. S&P TD is the specified brand on commercial projects — the standard TD range is the workhorse, TD Silent is the acoustically-insulated premium version, TD EVO is the EC version, and the range scales from 100mm to 500mm+. Elta Jetflow SJMF is a UK-made EC mixed flow range with strong efficiency figures, good for BREEAM and net-zero projects. Xpelair XIMX (XIMX100, XIMX100T, XIMX150) is the light-commercial/premium-residential option, often specified in new-build housing. Systemair Prio is the circular-duct equivalent in the Systemair catalogue.

How do I size a mixed flow fan?

Match three things: duct diameter (100mm, 125mm, 150mm, 160mm, 200mm, 250mm and up — the fan must match the duct, not be stepped down with a reducer), required airflow in l/s or m³/h (Building Regulations Part F gives 8–15 l/s for bathrooms depending on configuration, or 30 l/s intermittent / 13 l/s continuous for kitchens), and the static pressure the system imposes (duct length, bends, grilles, filters all add resistance). The fan's operating point on its published curve must sit above your design pressure, not at the free-air rating. If you only have duct size and target airflow, send the details and we'll check the curve for you.

Mixed flow or standard inline — which page should I buy from?

If your priority is quiet operation in a normal domestic or light-commercial extract job (bathroom, toilet, small office, kitchen extract over a domestic hood), buy from this page — mixed flow is designed exactly for that. If you're running a long commercial duct with heavy static pressure (carbon filtered kitchen extract, grow room, lab extract with filters), buy from the Inline Duct Fans page and pick a centrifugal model like the S&P VENT-NK or JETLINE. If you just need to move air down a short run with minimal resistance, a circular axial duct fan from the same page is cheaper and does the job.