How to choose a VMV exhaust unit

Choosing a VMV exhaust unit starts with the required airflow. Our range extends from 250 m³/h for a small installation up to 6000 m³/h for a workshop or a multi-occupancy building, with intermediate steps at 550, 750, 1500, 2700 or 3500 m³/h. The diameter of the connected duct must match this airflow: Ø125 mm suits small airflows, Ø160, Ø200 or Ø250 mm suit intermediate airflows, and Ø315 or Ø355 mm suit the highest airflows in the range. A duct that is too small increases air velocity, noise and pressure loss, and can reduce the actual performance of the installation.

The length of the ductwork run, the number of elbows and changes in diameter create additional pressure losses: never size a unit on its maximum rated airflow alone. The volume of the premises, the number of extract points and the use of the building also come into the equation. A premises ventilation installation needs larger ducting than a kitchen hood extraction installation at the same airflow.

Extraction unit or supply unit

An extraction unit draws stale air out of the premises and discharges it outside. A supply unit works the other way round: it introduces fresh air into the building, generally filtered to G4 grade, as on our G4 supply units of 2000, 3400 and 4000 m³/h. Depending on the configuration, extraction and supply are combined to balance a building's ventilation.

Compact, slimline or acoustic unit

The format is chosen primarily according to the available space. A slimline unit, such as our range in Ø125, Ø160, Ø200, Ø250, Ø315 and Ø355 mm, makes installation easier in a low suspended ceiling void. As a guide, on the standard (non-insulated) version of these slimline units, the sound level is around 40 to 44 dB in Ø125 and Ø160 mm, 45 to 48 dB in Ø200 and Ø250 mm, 46 to 50 dB in Ø315 mm and 47 to 50 dB in Ø355 mm. The acoustic version gains around 3 dB and reduces vibration in the ductwork, a point to watch closely near offices or occupied rooms. Several other references in the range are also available in an acoustic version, including the 7/7, 9/9, 10/10 and 12/12 units. Compact, lightweight and economical units (Poly range, from 250 to 3500 m³/h) suit installations where footprint, price and ease of installation are the priority.

Before choosing, check the unit's dimensions, the connection diameter, the power supply (the whole range runs on 230 V single phase) and the access required for maintenance, particularly if a pre-filter needs to be changed regularly.

Comparison table by airflow and diameter

VMV unit and commercial kitchen hood extraction

Some units in the range can be used for extraction on a commercial kitchen hood, provided the airflow, temperature resistance and ductwork configuration are suitable: this is the case, for example, with the 720 m³/h motorised unit sold as a kitchen hood VMV kit. A commercial kitchen installation should always be sized according to the cooking equipment and the extraction duct, not solely on the unit's airflow.

For installations requiring a smoke extraction solution or F400/120 fire resistance, please refer to our range of C4 smoke extraction units for public-access buildings (400°): these characteristics do not apply to the standard VMV units presented here.

Points to check before ordering

• The actual airflow required according to the volume of the premises, the number of extract points and the use of the building (offices, restaurant, workshop, school).
• The diameter of the existing or planned duct: if undersized, it limits performance at high airflow (pressure loss, overpressure, noise).
• The length of the ductwork run and the number of elbows, which always reduce the actual airflow compared with the free-air rating shown.
• The available fresh air inlet: without a sufficient inlet, the actual airflow drops and noise may increase.
• The space available for installation (suspended ceiling height, access for maintenance and filter changes where applicable) and, where noise is a sensitive issue, the difference between the standard and acoustic versions (around 3 dB less).

Complete your installation with

To protect a supply or pre-filtration unit, consider the G3 filter and the associated G3 filter box. The self-adhesive acoustic insulation roll complements an installation where noise is a concern. You will also find our professional mechanical ventilation accessories (ducts, fittings, grilles) and, for smoke extraction, our C4 smoke extraction units for public-access buildings (400°).