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Swirl Diffuser Selection Tool


Review the methodology to make sure it aligns with your project's requirements.

  1. Select US or Metric units (*required)

  2. Select the Airflow rate (CFM / CMH) (*required)

  3. Reduce the Noise value as necessary (NC) (optional).

  4. Reduce the Pressure Drop as necessary (in. w.g. / Pa.) (optional).

  5. The Results will populate the Technical Data Table along with an illustration of the diffuser.


Click here to jump to the table of Noise Criterion (NC) based on the ASHRAE Handbook.

Diffuser Size Calculator

Nomenclature:          CFM - Cubic feet per minute

CMH - Cubic meters per hour
NC-Noise Criterion

PD-Pressure Drop (Pascals / inches of w.g.)


Adicot is not affiliated, nor do we recommend any diffuser/grille manufacturers.  Any references or links to specific manufacturers are for illustrative purposes only. 


The Diffuser Size Calculator is a technical tool designed to assist engineers and HVAC professionals in calculating the appropriate size of diffusers for use in commercial and residential air distribution systems. The tool calculates the optimal diffuser size, taking into account factors such as air velocity, throw distance, static pressure, and air pattern dispersion. A properly sized diffuser is essential for ensuring that conditioned air is distributed evenly and efficiently throughout a building, which can help to improve indoor air quality and reduce energy costs. This tool can save time and effort for professionals who need to select and install the appropriate diffusers for their HVAC systems.

Diffusers are sized based on Airflow rate [CMH / CFM].  They can also be filtered by Noise Criterion (NC) (the table shows recommendations based on ASHRAE Fundamentals and room type) and Pressure Drop (PD). You can vary the NC or the PD (Pa. / in. w.g) to hone in on the correct diffuser size for your project. Below is a table of recommended noise criteria values based on Room Type.  The table values are based on ASHRAE's Handbook, Chapter 49, Noise and Vibration Control, Table 1,

Table of Diffuser/Grille Noise Criterion

Design Guidelines for HVAC-Related Background Sound in Rooms

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