I am a residential installer but from time to time I do some service calls. I’m having a hard time wrapping my head around what static pressure is and why it’s important
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[Static pressure](https://airfixture.com/blog/what-is-static-pressure-in-hvac) in relation to HVAC systems is the “resistance to airflow in the ductwork or other components within the system.” Higher static pressure = more work the HVAC has to do to force air into the room/building. An imbalance of static pressure and blowforce (“dynamic pressure”) can burn out the fans/motors in an HVAC or lead to hot/cold spots in a building. (According to the article linked, the most common cause of high static pressure is poor ductwork.)
Generally, static pressure refers to the amount of pressure exerted by a fluid (liquid or gas) at rest (Pressure = Force/Area).
For me and dealing with natural gas, static pressure is my gas supply pressure to the unit while it’s not running. My dynamic pressure is how much gas is in the line when the boiler is running. I want to know the difference between the two when I’m at full fire. I imagine it works pretty much the same with air and fluid pressures.
So there’s 2 main types of pressure in ductwork/HVAC; velocity pressure and static pressure.
Velocity pressure is the force of the air moving forward. Think about the speed at which it leaves the air diffuser, often measured in FPM (feet per minute).
Static pressure is the pressure of the air in all directions within a duct. Simply put, it’s a measure of your air going forward (same as velocity) but also a measure of the air pushing on the top, bottom and sides of your ductwork. If your static is too high, your air will not only come ripping out of your diffusers, but your duct will start to buckle outwards in all directions, and eventually break if the pressure builds. This is often measured in WC (water column).
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