In the last newsletter, we began a review of how to measure static pressure in an HVAC system. We discussed the required instruments and why measuring static pressure is such a good idea and a critical service we should be offering our customers. Let’s take a look and the steps required to measure total external static pressure.

Static Pressure Testing, Step By Step
It typically should take less than five minutes to measure a system’s static pressure. Here are sample instructions for a furnace and a remote coil:


STEP 2: Drill test holes using a 3/8-in. drill bit with a metal piercing tip. A bullet tip drill makes a clean round hole. Make sure to use your drill bit sheath (Described above) to prevent from drilling into the coil. If there’s duct liner inside, be sure to penetrate it to assure a good reading.


STEP 4: Read the supply or positive (+) static pressure by inserting the static pressure tip in the test hole into the air stream with the tip facing into the airflow. The magnet on the tip will hold it in place while the value is read and recorded. This measurement is the pressure the fan is "seeing" on the supply side of the system.

STEP 5: Read the return or negative (-) static pressure by moving the tube from the HIGH to the LOW-pressure port on the gauge. Insert the static pressure tip in the test hole on the return side with the tip facing the airflow. Read and record the negative static pressure. Don’t forget to insert hole plugs in the test holes when you’re done testing.

STEP 6: Calculate the system’s Total External Static Pressure by adding the two values. Since the negative and positive signs identify the type of pressure measured, you can ignore them when adding the two values together.

For example:
The supply static pressure reading is (+) .26 w.c.
The return static pressure reading is (-) .21” w.c.
The total system static pressure is .47” w.c.

.26” + .21” = .47” w.c.

Further testing may include pressure drop measurement to determine the contribution of each component to total external static pressure of the system.


If static pressure is too high, you have evidence of problems with the system causing low airflow. Check for blockage in ducts, closed dampers, improper transitions, offsets or kinked flex duct. The problems can also be from the equipment and system accessories like “High Efficiency” cooling coil or restrictive filters.

Low static pressure can also mean trouble. Low pressure may indicate leaking ductwork or plenums, missing filters, low fan speed or separated ductwork.

The Opportunity
The answer to improving system performance is often found outside of the box. (The equipment) Static pressure allows you to "see" the system in an entirely new light — airflow nearly becomes visible. Airflow is directly connected to BTU’s. When airflow is brought into the equation, your ability to diagnose and solve problems multiplies, as you’re able to "pull your head out of the box" and see the system as a whole.



Static pressure measurement unlocks the door to the system as a whole.

You can gain access to the amazing amount of duct repair and renovation work from the systems you service every day. The margins are extremely high and the skills required to perform duct renovation are minimal.
