How to Measure CFM and H2S

How to Determine Airflow and H2S Concentration of a Sewer Vent Line

Other than the vent pipe size, to accurately size any of our filters, you will need to know two things: a) the velocity of the air moving through the vent; and b) the concentration of the hydrogen sulfide (H2S) in the airstream.

Measuring the H2S Concentration

Measuring the concentration of hydrogen sulfide (H2S) in a septic vent airstream can be accomplished using portable H2S detectors which are commonly available and provide real-time readings. They are suitable for monitoring in environments with varying concentrations. You can find these on Amazon and other websites. Here is a link to one on Amazon.


Determining the Airflow (CFM)

To determine the airflow of a septic vent, you can use an anemometer. This is the most effective tool for measuring airflow.

    • Insert the anemometer into the vent pipe.
    • Measure air velocity in cubic feet per minute (CFM) at multiple points across the cross-section of the vent.
    • Calculate the average velocity from these measurements.

Before starting any measurement, ensure safety protocols are in place, as H2S is toxic. Consider conducting measurements during periods of typical venting activity to get accurate representations of concentrations.