How to choose a 2-speed roof fan

A 2-speed roof fan operates with two distinct speeds, shown as a dual airflow figure on each reference (for example 2,000 to 4,200 m³/h for the T4048-TRI). Low speed is enough outside of service rush, high speed takes over during busy periods. That is the whole point of the system compared to a single-speed roof fan: you match the airflow to actual activity in the premises, without running the motor at full power all day.

This type of roof fan is commonly used on professional mechanical ventilation and smoke extraction systems, where two operating speeds are a natural fit, whether for a new installation or to replace a faulty motor. In commercial kitchens, however, these models are intended for like-for-like replacement of an existing 2-speed roof fan: if you are fitting out a new kitchen, ask our technical team for advice before choosing this type of product.

The first thing to check is the airflow required for your system. Our range covers 2,000 to 24,000 m³/h depending on the model, from the T4048-TRI (2,000 to 4,200 m³/h) up to the T80612-TRI (12,000 to 24,000 m³/h) for the largest installations or central production kitchens. In between, the T4548, T50612, T5048, T5056, T5646 and T5648 cover the most common intermediate airflows.

Second point: the power supply. All models in this range run on 380V three-phase, which means a three-phase supply must be available on site. Check this before ordering, especially on a replacement job where the old motor may have been single-phase.

2-speed roof fan or roof fan with speed controller: what is the difference

The 2-speed roof fan offers two fixed settings, controlled by a 2-speed starter and a simple switch or button. It is a robust, cost-effective solution when two speeds are enough to cover your needs, and it is also the usual setup for professional mechanical ventilation and smoke extraction installations. If you need progressive airflow adjustment rather than two fixed steps, look at our roof extract fans, which are compatible with a speed controller depending on the model, allowing finer adjustment.

Comparison table of 2-speed roof fans

Points to check before ordering

• Kitchen use: in commercial kitchens, these 2-speed roof fans are fitted as like-for-like replacements for an existing 2-speed model. For professional mechanical ventilation or smoke extraction, they suit both new installations and replacements.
• Actual expected airflow: the free airflow stated on each product page is reduced according to the length of the ductwork, the number of elbows and the condition of the filters. Do not size your system on the maximum airflow figure alone, ask our team for advice based on your configuration (hood, cooking type, duct length and diameter, elbows).
• Air inlet: effective extraction requires a sufficient air inlet in the premises, otherwise actual airflow drops and negative pressure or noise increases.
• Diameter and ductwork: a duct that is too narrow or a system that is too long increases pressure losses. Take your measurements (ceiling height, duct diameter and length, elbows) before choosing a model.
• Thermal protection: if the motor stops after 10 to 15 minutes of running, this often points to a tripped thermal protection. Check for excess pressure, the ductwork, the air inlet and the electrical supply.
• Mounting accessories: vertical or horizontal discharge, fitting on ductwork or on a roof kerb. Check that the deflector kit or mounting kit is compatible with your exact model before ordering.

Complete your order with

Complete your roof fan with a 2-speed starter with smoke extraction button or a simple 2-speed switch for local control. For roof mounting, also consider the roof kerb for roof fan, the duct mounting kit for roof fan or the vertical deflector kit if you need to redirect the discharge.

All these roof fans are manufactured in France and covered by a 1-year professional warranty. VentilSoGood supplies this equipment but does not carry out installation: fitting must be entrusted to a qualified professional.