Inline & Mixed Flow Fans

Frequently asked questions

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, generating higher static pressure, so it pushes air effectively through longer or more complex runs with bends and restrictions. That extra pressure is why mixed flow units hold their airflow on branched and multi-room systems where a plain axial inline fan would fall away. For most domestic installations the mixed flow fan is the more versatile choice.

Is an inline fan an axial fan?

An inline fan can be axial, but not all are. The word inline describes where the fan sits, within the duct, rather than how the impeller works. Axial inline fans suit short, low-resistance runs. Mixed flow inline fans add centrifugal performance for higher-pressure systems. Check the pressure curve rather than the name on the box. For larger plate, cased and bifurcated units see our axial fans.

What size inline fan do I need?

Match the fan's connection size to your existing ductwork. 100mm, 125mm, 150mm and 200mm are the most common domestic sizes. For airflow, a working rule is 10 air changes per hour for bathrooms and kitchens: room volume in cubic metres multiplied by 10, divided by 60, gives the minimum litres per second. Increase that figure for longer duct runs or multiple outlets, because every bend, grille and metre of flexible duct takes airflow away from the headline rating.

Can an inline fan serve multiple rooms?

Yes. A single inline fan can be connected to several extract points through branched ductwork, which makes it a cost-effective route to a whole-house MEV installation. S&P and Systemair both offer models suited to multi-room extraction. Size for the total extract volume plus the resistance of the whole branch network, not for one room.

Where should an inline fan be installed?

Inline fans are usually installed in loft spaces, ceiling voids or service cupboards, anywhere accessible within the duct run. Keep the motor away from the extract grille so noise is not transmitted straight into the room. Leave access for maintenance and filter changes, since a fan buried behind a sealed ceiling is a problem you only get to solve once.

Are inline fans loud?

Generally quieter than wall or ceiling mounted extractors, because the motor is out of the occupied space and the duct run absorbs some of the noise on its way to the grille. Actual levels depend on the model, the duct material and how far the fan sits from the outlet. Mixed flow and dMEV type inline fans are designed for particularly low noise. Where noise is critical, mount the fan further along the run and use an acoustic duct section.

What is a dMEV inline fan?

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

Can inline fans be speed controlled?

Most can. Many models have a two-speed or trickle and boost setting built in, and AC units can be run through an electronic or transformer controller to trim them to the duty you actually need. EC models take a 0 to 10V signal directly. See our fan speed controllers, and check the controller matches the motor type, because AC and EC need different control. Running a slightly oversized fan at reduced speed is quieter than running a smaller fan flat out.

Do you supply inline fans for trade and project work?

Yes. We supply M&E contractors, installers, developers and facilities teams, and hold stock across the main inline and mixed flow ranges for next day delivery. Send a schedule, a drawing or a duty list and we will price the lot and confirm sizes and controls alongside. Call 0161 399 3825 or email hello@efans.co.uk.