Static pressure refers to the forces acting on the inner surfaces of HVAC system ductwork. It serves as an indicator of airflow and can be affected by numerous forms of resistance, including the filter, coil, and design of the duct system.

Static pressure readings offer insight into a system’s effectiveness and efficiency. In addition to serving as an indicator of a system’s health, HVAC contractors may use it as a gateway for system improvements and upsells. Unfortunately, though, many technicians choose not to complete static pressure tests, providing a disservice to customers and leaving potential operational and financial gains on the table.

How to Measure Static Pressure

Total external static pressure (TESP) can be identified by placing a manometer probe above the filter and another adjacent to the blower. Manometer probes should point in the opposite direction of airflow to yield the most accurate readings.

Static pressure may either push against the ductwork (positive, on the supply side) or pull against it (negative, on the return side). A technician can measure airflow resistance by adding the readings together.

Numerous obstacles within the system may create unnecessary airflow resistance, said Jesse Testerman, senior technician, Kalos Services, Clermont, Florida.

“Dirty coils or filters can reduce the supply static pressure and will make the TESP low if static pressure is measured before the filter in the return, which can be a misleading airflow indicator,” he said.

When using a manometer as a diagnostic tool, readings can be obtained with or without the filter. A comparison of the two measurements can help determine how much the filter (clean or dirty) may be contributing to the system’s static pressure drop.

“We typically want to see a static pressure of less than or around 0.5-inch WC [water column],” said Testerman. “Once we reach 0.8-inch WC or higher, we start to see reduced blower motor efficiency, shorter blower life spans, and more overall issues.”

Manometers can also be used to locate duct restrictions, as obstacles, such as collapsed ducts, may cause static pressure to increase as the airflow reaches the restriction.

To measure the static pressure drop across the coil, place a manometer probe before the filter or immediately before the blower (above the coil). The reading should show a negative static pressure.

“Some diagnostic apps may have trouble calculating TESP readings in those locations, so you may have to do the math yourself to figure out the pressure drop across the coil,” said Testerman.

Explaining Static Pressure to Customers

In all of her years, Nancy McKeraghan, co-owner, Canco Climate Care, Ontario, Canada, has never received a call from a customer complaining about high or low static pressure.

“Customers simply don’t understand static pressure or the issues it may cause,” she said. “We have to educate them so that they understand exactly what their needs are. Technicians have to take the necessary readings, provide evidence through evaluations, and offer the appropriate solutions.” Describing those problems and solutions can be challenging. To simplify the science, the National Comfort Institute Inc. (NCI) utilizes a custom-designed blood pressure chart. The diagram explains a system’s “health” in a simple, easy-to-understand visual.

“It doesn’t matter if a patient has a stuffy nose or a broken leg, a blood pressure reading is taken on every visit,” said David Richardson, director of training, NCI. “HVAC contractors should take the same approach.”

Static pressure readings, much like blood pressure readings, provide technicians with valuable baseline information and clues to underlying, invisible issues that could be otherwise missed in an HVAC system, said Richardson.

“If a doctor reports high blood pressure, and hints that a heart attack may be on the horizon, patients should be privy to potential solutions,” he said. “Your customers have the same concerns regarding their HVAC systems. If you can predict a premature failure of their system due to high static pressure, shouldn’t they know about it and be offered solutions to correct the problems?”

When Should a Static Pressure Measurement Occur?

Brian Wright, owner and principal, Crossway Mechanical LLC, Tomball, Texas, said his company performs static pressure measurements every day.

“It takes us around 10-15 minutes to drill the ports and test a single-stage system,” he said. “Zoned systems take around 30-45 minutes, because we test each zone. Some homes in our area have three or four zones, so it takes a bit more time.”

When asked how frequently a static pressure test should occur, John Whitehead, co-owner, Honest Heating and Cooling Inc., succinctly replied: on every visit and every piece of HVAC equipment.

“Proper system performance directly affects a customer’s security, safety, and comfort,” he said. “It’s important for us to make sure we’re optimizing each of these attributes for our customers. If we’re not performing static pressure readings, we’re not doing our job to the best of our ability.”

Mark Johnson, vice president, TM Johnson Bros., Grandy, Minnesota, said his company requires static pressure readings on every job, no matter how busy the company’s technicians are.

“We’ve established a culture that calls for a static pressure or combustion test on every call,” he said. “By doing so, we’re creating a savings account for the shoulder seasons. I’d wager about 90% of our customers have static pressure issues, and we’re not doing them justice by not testing or bringing these issues up on every visit.”

Customer Delight

A properly executed static pressure test often leads to more comfortable customers with healthier systems. And happy customers lead to greater customer relationships and more referrals.

“We strive to have a strong customer relationship at every touchpoint,” said McKeraghan. “That rings true when it comes to static pressure, as we want to ensure customers’ systems are running optimally.

“We call customers to remind them of their annual maintenance checks and make conversational notes to follow up with customers who may have been out of town, asking them how their trip went,” she continued. “We are not box sellers; we're solution providers. Most of our customers come from referrals. So that, to me, means we're doing a great job.”

A static pressure test verifies if a system is running improperly and that you’re capable of diagnosing such a problem, said Michael Greany, manager, Aire Rite Air Conditioning.

“Static pressure provides us an opportunity to improve the lives of our customers,” he said. “The data that’s collected shows that improvements need to be made. While customers may not move forward with a solution, it’s your job, as an HVAC professional, to do everything you can to identify and communicate the problem.”