Advanced airflow calculation tools for HVAC professionals

Our specialized calculators are designed to simplify and optimize your ventilation projects. Thanks to our advanced calculation tools, you can accurately size your air duct networks and optimize the acoustics of your installations.

Discover our 4 specialized calculators for optimal ventilation that meets your professional requirements.

Calculator duct pressure drop Cairox

Duct pressure drop calculator

Calculate the linear pressure drop in air distribution networks in an instant. You can also calculate this pressure drop for certain air distribution accessories as a function of flow rate or throughput velocity.

This tool instantly calculates the linear pressure drop in circular and rectangular air networks as a function of flow rate and through velocity.

This tool is useful for dimensioning your ventilation systems.

Calculateur conduit aéraulique

An alternative: the flow control ruler


Display the flow rate either in front of the speed V (red scale). or in front of the coefficient J (black scale), as required.

The theoretical Ø is displayed in front of the ▼ on the upper scale.

The lower scale is reserved for Ø measurements from the NFP 50-401 standardised series.

By positioning the ▲ in front of the actual Ø which is closest in the series used, the exact values for V (red scale) and J (black scale) are displayed.



Data: Flow rate and speed V required

Position the flow rate in front of V (red scale). Align the chosen L and H values (red scale). The exact V value is displayed in front of the flow rate. The J value is displayed in front of the flow rate after aligning the chosen L and H values (black scale).

Note that L is always the larger dimension.

Optimum duct diameter calculator

Optimum duct diameter calculator

Quickly find the duct diameter best suited to your needs, based on the desired air flow rate and the air velocity in the network. The tool will give you the diameter best suited to your needs, with results up to 1250 mm in diameter. Cairox lets you calculate the duct diameter needed to circulate air at a certain speed, based on the flow rate you enter.

The calculation formula used is the classic flow rate = velocity x surface area, and each parameter in the equation must be entered in the most common units: flow rate (m3/h), surface area (m²) and velocity (m/s).

These air flow rates depend on several factors: the type of building and the positioning of the ducts in the distribution network.

Sound converter Cairox

Sound conversion calculator

This CAIROX calculator determines the sound pressure (Lp) at a specific point using the sound power level (Lw), distance and directivity. It enables conversion between the two most important physical quantities of acoustics in ventilation: sound power and sound pressure.

Sound power (Lw) corresponds to the eigenvalue of sound at the sound source.

From this data, we need to start calculating sound pressure (Lp), which corresponds to the noise level when sound waves propagate in the environment. Sound pressure is therefore a key factor in determining what the listener will perceive. To go from power to pressure, we need to take into account the placement of the sound source and the distance between the listener and the sound source.

Calculating the sum of 2 sound levels

Calculating the sum of two sound power levels.

The CAIROX calculator allows you to calculate the sum of two sound levels in dB(A).
Since noise levels are measured on a logarithmic scale, they do not add up mathematically.

We must therefore use the following formula: Lp = 20 x log10 [Peff/Pref ] where Peff = effective pressure, Pref = reference pressure Lp = sound pressure.

For example, if you add two identical sounds, the effective pressure will be doubled in the previous formula. The result is then : Lp = 20 x log10 [2xPeff/Pref ] = 20 x log10 (2) + 20 x log10 [Peff/Pref ] = 3 + 20 x log10 [Peff/Pref ]

Consequently, this sum of 2 identical sound levels corresponds to a 3dB increase in the overall level.