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Community and Q&A

Probe Locations for Checking Static Pressure

aston01 | Posted in Mechanicals on
Where would you put the probes in this system to check static pressure?
Most of the examples I have seen for probe placement are for pretty standard configurations, but due to space limitations, this ducted mini-split doesn’t have much straight air near the unit. Where could I place the probes to have a higher likelihood of getting an accurate result?
If I also wanted to measure the pressure drop over the filter how close should I measure to the filter with duct transition like this?

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  1. Expert Member
    Akos | | #1

    Static pressure is not like air flow, it can be measured anywhere. Drill the port where you want, probe should not protrude into the duct.

    If you want to measure air flow, generally you want the pitot tube to be in a straight section about 10x duct diameters for any transition.

    For slim ducted units I find it easier to home run rooms. This means a simple box plenum right at the outlet with takeoffs for each room. Dampers at the takeoffs to balance flows, easily accessible from the service panel under the unit. A bit more ducting but simpler install.

    1. Deleted | | #3


  2. Expert Member
    BILL WICHERS | | #2

    To add to what Akos said: the only requirement is that the probe be placed at 90 degrees to the airflow so that the air velocity doesn't influence the reading. I would probably put the test port somewhere near the main unit in an easy to reach spot.

    To measure pressure drop across the filter, you really want a DIFFERENTIAL manometer that has TWO ports. You would then measure immediately before and immediately after the filter, with your probes 90 degrees to the airflow, ideally using ports in easy to reach spots. You can use a "regular" (non-differential) manometer too, but then you have to take two measurements, one ahead of, and one after, the filter, and then calculate the difference to determine the pressure drop across the filter.


    1. aston01 | | #4

      Good to know.

      I have a Testo 510i to check the measurements with but the angles on the duct transitions around the filter had me a little confused as to their effect on probe placement and whether the orientation to the filter or the duct took priority. Based on Akos comment it's not as sensitive as I might have originally thought.

      1. Expert Member
        BILL WICHERS | | #5

        Ideally you want to make measurements somewhere the air flow is linear, so not at or near a fitting. The ideal spot is usually near the middle of a long, straight section of ductwork. You want to put the probe in the middle of the side of the duct too, so approximately equidistant from the wall on either side of the duct in the location of the probe.


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