Fan Speed Controllers

Frequently asked questions

Do I need an AC or EC fan speed controller?

It depends entirely on your fan's motor type, as they are not interchangeable. AC fans use mains-voltage controllers that reduce the voltage or phase angle to slow the motor down. These are the triac controllers (like the Systemair REE range) and transformer controllers (like the Systemair ITR range). EC fans have their own built-in electronics and just need a low-voltage control signal, typically 0-10V DC, to set the speed. Controllers like the Systemair MTP10 or EAC send that signal. Connecting an AC controller to an EC fan will damage the motor electronics. If you are unsure which motor type your fan has, check the product datasheet or call us on 0161 399 3825 and we will confirm which controller you need.

What is the difference between a triac and a transformer speed controller?

Both control AC fan motors, but they work differently. A triac controller (like the Systemair REE) chops the mains waveform to reduce the effective voltage. It is compact, cheap, and works well on small single-phase fans up to about 1.5A, but triac controllers can cause motor hum on some fans. A transformer controller (like the Systemair ITR) reduces voltage using a multi-tapped autotransformer. It is heavier and more expensive but gives cleaner power and smoother speed control with no motor hum. For fans above 2 to 3A, or where noise matters in offices, bedrooms and meeting rooms, a transformer controller is usually the better choice.

What amp rating do I need for my speed controller?

The controller's amp rating must be equal to or greater than the fan's full load current (FLC). Check the nameplate on your fan or the product datasheet for the FLC in amps, listed as the maximum current draw at full speed. A fan drawing 2.1A needs at least a 3A controller. Never undersize the controller, as it will overheat and fail. If you are running two fans from one controller, add both FLCs together and choose a controller rated above the combined total. For future-proofing, it is good practice to go one size up from the minimum.

Can I control multiple fans from one speed controller?

Yes, as long as the total combined current draw of all fans does not exceed the controller's amp rating, and all fans are the same motor type (all AC or all EC). For AC fans, connect them in parallel to the controller output. For EC fans, connect the 0-10V signal in parallel, as each fan's electronics draws negligible current from the signal wire. This is common in commercial kitchens where supply and extract run together, and in warehouse ventilation with multiple plate axials on one controller. If the fans need to run at different speeds, they each need their own controller.

When should I use a thermostat or sensor with my fan controller?

When you want the fan speed to respond automatically to conditions rather than being manually set. A room thermostat (like the Systemair RT 0-30) switches the fan on or adjusts speed when the room temperature exceeds a set point, common in server rooms, kitchens and warehouses. A duct-mounted PT1000 sensor measures the air temperature inside the duct and feeds that reading to a compatible controller for automatic modulation. Use thermostats for simple on/off or two-speed control; use duct sensors with BMS-compatible controllers where you need proportional speed control based on real-time conditions.

Which controller do I need for an MVHR or MEV unit?

Most MVHR and MEV units have their own built-in speed control, so you do not normally add an external speed controller. What you might need is a wired remote controller (like the Vent-Axia 443283) that lets you adjust boost speed, view filter status, or switch between ventilation modes from a wall-mounted panel. Some units also accept a trickle/boost switch (like the Vent-Axia 455213) wired to the bathroom or kitchen, which triggers boost mode when switched on, typically connected to the light circuit or a separate pull-cord switch. Check your MVHR unit's installation manual for compatible controllers before ordering.