HVAC School - For Techs, By Techs Static Pressure is like Blood Pressure - Short #258
In this short podcast episode, Bryan explains the science behind a common HVAC simile: static pressure is like blood pressure. He covers the similarities and differences between measuring static pressure during a service call or maintenance and a doctor measuring your blood pressure at a checkup.
Total external static pressure (TESP) should be measured every time you perform service or maintenance on a unit. The exact test port location will vary between air handlers and furnaces; the coil adds extra pressure drop in furnace applications. You need to pick a coil that has the lowest static pressure drop (same consideration as filters). Typically, the lower the pressure drop, the better. Make sure you use proper ports for static pressure testing when you do make those holes.
Static pressure isn't airflow itself. It can help diagnose airflow issues or give indications, but it doesn't measure the CFM. Static pressure is a balloon-type pressure exerted on the walls of the duct. Just as high blood pressure doesn't mean your heart is pumping more blood than it should, a high static pressure doesn't mean your blower is moving a lot of air; both can indicate restrictions.
You also don't want an extremely low static pressure, either. It could indicate that airflow is weak, just like a very low blood pressure indicates that the heart isn't pumping as it should. If you want to know your system airflow, you should use TEC's TrueFlow grid. However, static pressure is particularly good at measuring trends so that you can see where the numbers deviate from the norm for each individual system.
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