How to choose a VMC, AHU or boiler room fan motor

To replace a VMC fan motor without any nasty surprises, four criteria matter most. First, the airflow: our range spans from 720 m³/h (DD133/190) to 6,000 m³/h (DD12/12), with most demand falling between 1,300 and 3,600 m³/h on the 7/7 and 9/7 sizes. Next, the motor size (7/7, 7/9, 8/9, 9/7, 9/9, 10/10, 12/12): it must match the dimensions of your impeller and fan box, not just the original brand. The power supply: all our double-inlet centrifugal fans run on 230V single-phase, which simplifies replacement on most commercial installations. Finally, the direction of rotation, which should be checked before ordering if your ductwork requires a specific configuration.

A ductwork system that is too long, with many elbows or significant pressure losses, will reduce the actual airflow achieved compared with the motor's rated airflow. If your installation is old or complex, it's best to work from a cautious estimate rather than aim for the theoretical maximum airflow.

Double-inlet centrifugal fan sizes and their uses

The double-inlet centrifugal fan works on the principle of centrifugal force to draw in air and push it through the ductwork. For a small plant room or a compact replacement, the DD133/190 and DD146/190 or DD146/180 references cover 720 to 1,400 m³/h. For a communal VMC system or a standard unit heater, sizes 7/7 and 7/9 (1,300 to 2,600 m³/h) are the most sought after, often available in a 3-speed version to adjust airflow according to the building's needs. Beyond that, sizes 9/7 and 9/9 go up to 3,600 m³/h and suit larger air handling units or boiler rooms. For the highest airflows, the DD10/10 (3,600 m³/h) and the DD12/12 (up to 6,000 m³/h) complete the range.

Comparison table of double-inlet centrifugal fans

Replacing an existing motor: what to check

To find the right replacement motor, don't rely solely on the brand of your current installation (VIM, ALDES, CAIROX, etc.): S&P, Tecnifan, Nicotra - Regal and others offer motors of equivalent sizes (7/7, 9/7, 9/9, etc.) that can be substituted for one another if the dimensions match. Compare, first and foremost, the dimensions of the motor and impeller, the airflow, the voltage (230V single-phase in our range) and the direction of rotation. If in doubt, send us a photo of your old motor's nameplate along with its dimensions: we can help you identify the closest model.

Points to check before ordering

• Required airflow: as a guide, the actual airflow depends on the ductwork system (length, elbows, filters) and not only on the motor's rated airflow. Allow a margin if your installation has many elbows.
• Size and direction of rotation: check the fixing centre distance and the direction of rotation of your old motor before ordering a replacement.
• Power supply: all motors in this range run on 230V single-phase; check that your installation is compatible before ordering.
• Signs of wear: significant vibration, unusual mechanical noise, a motor that overheats or a drop in airflow are often signs of wear in the motor, impeller or bearings. Also check that the ductwork isn't blocked before replacing the part.
• Parcel weight: from 5 kg for the smallest motors up to 25 kg for the DD12/12, a useful guide for planning handling on receipt.

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