Inline & Mixed Flow Fans

Inline and mixed flow fans are installed within the duct run itself — away from the room being ventilated — making them significantly quieter in use than wall or ceiling-mounted fans. They're the right choice wherever a longer duct run is needed, where noise levels matter, or where a single fan needs to serve multiple outlets. Our range covers connection sizes from 100mm to 315mm with airflow rates up to 1,728 m³/h, stocking over 200 models from Vent-Axia, S&P, Systemair, Elta, Manrose, Xpelair, and Hydor.

What is the difference between an inline fan and a mixed flow fan?

A standard inline (axial) fan moves air straight through in one direction and works well on short, straight duct runs. A mixed flow fan combines axial and centrifugal airflow principles, generating higher static pressure — meaning it can push air effectively through longer or more complex duct runs with bends and restrictions. For most domestic applications, mixed flow fans are the more versatile choice.

What size inline fan do I need?

Match the fan's connection size to your existing ductwork — 100mm (4"), 125mm (5"), 150mm (6"), and 200mm (8") are the most common domestic sizes. For airflow rate, use the rule of thumb of 10 air changes per hour for bathrooms and kitchens, and calculate: room volume (m³) × 10 ÷ 60 = minimum l/s required. For longer duct runs or multiple outlets, increase the rated airflow accordingly.

Can an inline fan serve multiple rooms?

Yes — a single inline fan can be connected to multiple extract points via branched ductwork, making it a cost-effective solution for whole-house MEV (Mechanical Extract Ventilation) installations. S&P and Systemair offer a number of models specifically suited to multi-room extraction.

Where should an inline fan be installed?

Inline fans are typically installed in loft spaces, ceiling voids, or service cupboards — anywhere accessible within the duct run. The motor should be kept away from the extract grille to minimise noise transmission into the room. Always ensure the unit is accessible for maintenance and filter changes.

What is a dMEV inline fan?

A dMEV (decentralised Mechanical Extract Ventilation) inline fan runs continuously at a low trickle rate, boosting to a higher speed when humidity or occupancy increases. They satisfy Building Regulations Part F for continuous ventilation and are a quieter, more energy-efficient alternative to intermittent fans that run only when a light switch is activated.

Frequently Asked Questions

What is a mixed flow inline fan?

A mixed flow inline fan combines axial and centrifugal airflow to deliver higher static pressure than a standard inline fan. It is suited to longer or more complex duct runs, including bends and multi‑room MEV systems, while staying relatively quiet.

What are the advantages of mixed flow fans?

Mixed flow fans give higher pressure, so they maintain airflow through longer or branched ducts. They are quieter and more versatile for multi‑room or whole‑house systems than basic axial extractors.

What is the difference between axial and mixed flow fans?

Axial fans move air in a straight line and suit short, simple duct runs. Mixed flow fans add centrifugal action, giving higher pressure and better performance on longer or more complex systems.

When to use an inline fan?

Use an inline fan when the unit must be concealed, in lofts, ceiling voids, or service cupboards, or where longer duct runs, multi‑room extraction, or lower noise are required.

Is an inline fan an axial fan?

An inline fan can be axial, but not all are. Axial inline fans suit short, low‑resistance runs; mixed flow inline fans add centrifugal performance for higher‑pressure systems.

Are inline fans loud?

Inline fans are generally quieter than wall‑ or ceiling‑mounted extractors because the motor is out of the occupied space. Noise depends on model, with mixed flow or dMEV‑type inline fans designed for especially low‑noise operation.