Using simple tissue strips and a mist generator, we compare the airflow from one of our FunGuyEquipment flow hoods with the HEPA filter installed against the same unit with the filter removed. The difference is very clear. With the filter installed, the airflow is steady, even, and consistently moving forwards. With the filter removed, the fans create unstable, chaotic airflow with visible shaking, rolling, and reverse movement.
Test 1: Tissue Strip Test With the Filter Installed
In this first test, tissue strips are attached in front of the filter face. This makes the airflow easy to see.
With the filter installed, the tissue moves evenly and steadily across the face of the hood. There is very little shaking, and most importantly, the tissue does not get pulled backwards toward the filter by turbulent air movement.
Test 2: Tissue Strip Test With the Filter Removed
This second test shows the opposite condition. The filter is removed, so the fans are blowing directly out of the unit with no filter restriction and no smoothing effect from the HEPA filter.
The result is a much more chaotic airflow pattern. The tissue shakes aggressively and, at times, gets pulled backwards by turbulent movement. This is exactly what we do not want in a sterile work area.
Test 3: Mist Test With the Filter Installed
In this test, a mist generator is moved across the face of the flow hood, from side to side and up and down.
The mist shows steady and even forward movement across the whole filter face. There are no obvious dead spots, no visible backward movement, and no rolling turbulence pulling mist back into the hood.
How This Compares to an Industrial flow hood
Our mist test is a simple visual demonstration, but the method is very similar to the example below, an industrial flow hood is tested using a smoke generator. The smoke forms a visible forward-moving stream away from the filter face. Please note, this video is played at 1/8th speed in places.
Test 4: Mist Test With the Filter Removed
This test again shows the unit with the filter removed. The fans are blowing directly onto the mist generator, creating high airflow but without the stabilising effect of the filter.
The mist shakes, rolls, and moves unpredictably. You can see the airflow breaking up and moving in different directions, including visible pull-back in places.
Test 5: Mist Flow Distance Test With the Filter Installed
In the final test, the mist generator is moved away from the filter face, up to around 2.4 metres.
Even at that distance, the mist still shows a clear, stable forward direction. The flow has not collapsed due to turbulence.
This does not mean you should work 2.4 metres away from the hood. Sterile work should be done close to the filter face. However, this test is a strong visual demonstration of how stable the airflow remains.
Why This Matters for Mushroom Cultivation
When working with agar, grain, liquid culture, or sterile tools, the aim is to protect the working area with a steady stream of clean filtered air.
If the airflow is unstable, it can roll, swirl, and pull unfiltered room air back into the work area.
Inside our flow hoods, we use internal air guides to help distribute the air from the fans as evenly as possible before it even reaches the HEPA filter. This reduces concentrated airflow directly from the fans and gives the filter the best possible chance to further smooth and refine the air before it exits the front face.
