When you go to the doctor, one of the first things they check is your blood pressure. It is quick, it says a lot about your overall health, and it often points to problems before you feel them. Your HVAC system has a number that works the same way: total external static pressure.
What it measures
Static pressure is the resistance your blower has to push against: the filter, the coil, the ductwork, the registers and grilles. It is measured in inches of water column (" w.c.).
Most residential blowers are designed to work against about 0.50" w.c. When static pressure is well above that, the system cannot move the air it was designed to move.
Why it matters
- Less airflow means less cooling and heating actually reaches your rooms.
- The blower motor works harder, uses more power and wears out sooner.
- Low airflow throws off refrigerant readings, which can lead to a misdiagnosis.
- Rooms at the end of long duct runs get starved for air.
Common causes of high static pressure
- A filter that is too restrictive for its size, or simply dirty
- A return that is too small for the system
- Crushed, kinked or undersized ducts
- A dirty indoor coil
- Closed or blocked supply registers
What we do with it
We measure static pressure on every system test. It is one of the five areas in the 0 to 100 System Vitals score we give every customer, along with airflow, refrigerant charge, delivered capacity and operating conditions.