Many answers to my previous article, How to Balance a Residential HVAC System, asked about static pressure HVAC measurements. Let’s stick with the basics and see how to measure static pressure in 6 easy steps.
Stepwise static pressure test
Static pressure measurement in a residential system typically takes less than 5 minutes. Here is an example of an oven and external coil procedure.
Step 1:
Find suitable locations for drilling test holes on the supply side (+) between the oven and the coil and the return side (-) between the filter and the oven. Center the test port for a cleaner look. Stay away from coils, cap tubes, drain pans, or circuit boards to avoid damage. Be sure to watch before drilling.
Step 2:
Drill a test hole with a 3/8-inch drill—a drill bit with a metal tip. Make a clean round opening with a ball drill. Always use the drill sleeve (above) to prevent drilling into the coil. If there is a duct liner inside, pierce it to ensure readings.
Step 3:
Slide one end of the hose onto the static pressure spike. Attach the other end of the hose to his HIGH (+) pressure port on the gauge. If necessary, ensure the meter is level and adjust the front screw with a small screwdriver to zero. Check the instruction manual for digital because the measured value is different for each zero. Step 4:
Insert the static pressure tip into the test port and point the tip into the airflow to read the applied or positive (+) static pressure. A magnet at the end holds it in place while reading and recording the value. This measurement is the pressure the fan “sees” on the supply side of the system.
Step 5:
Move the hose from her HI port on the gauge to the LOW port to read the rear static or negative pressure (-). Insert the static pressure tip into the return side test port and point the tip towards the airflow. Read and record the negative static pressure. Don’t forget to connect the connector to the test port after testing is complete.
Step 6:
Add the two values to calculate the total external static pressure of the system. The negative and positive signs identify the type of pressure being measured, so you can ignore them when adding the two values.
For example:
- The static supply pressure reading is (+) 0.26 w.c.
- The static return pressure reading is (-) 0.21 in. w.c.
- The total static pressure of the system is 0.47 in. w.c.
0.26 inch + 0.21 inch = 0.47 inch w.c
National average residential static pressure
Unfortunately, the example above is misleading. The average total external static pressure for US residential buildings for a 0.50-inch rated system is 0.82 inches.
Converting static pressure to blood pressure means that the average blood pressure in the United States is 130 higher than 200. Doctors confirmed that patients with blood pressure 130 and over 200 should not leave their clinics or hospitals until a solution to their problem has been found, and their blood pressure is close to normal.
Static pressure diagnosis
Static pressure diagnostics are easy. Compare the rated external static pressure to the device’s maximum total external static pressure.
HVAC pressure diagnostics have similarities to blood pressure diagnostics. Good blood pressure is 120 and above 80 by most standards. High blood pressure is bad and usually indicates an overly restricted artery.
Similarly, an external total static pressure higher than the total external static pressure may indicate an excessive restriction of the air distribution system.
If your blood pressure is lower than expected, you may have a weak heart or a leaky artery.
The air distribution system may be overly restricted if the total external static pressure is greater than the rated total external static pressure.
The exact diagnosis is often applied to low total external static pressure. Very low static pressure could indicate a slow fan speed or a leak in the duct system.
Further testing may include pressure drop measurements to determine the contribution of each component to the total external static pressure of the system.
Measuring the static pressure of a system designed and installed by a company can provide great insight into system performance. Is it any wonder that 98% of maintenance contracts exclude waterway systems? Clearly, the pendulum has swung wildly in the direction of comfort and away from comfort.
High static pressure indicates low airflow—checks for clogged ducts, closed flaps, improper transitions, offsets, and kinks in bent ducts. Problems can also arise from equipment and system accessories such as “high efficiency” cooling coils and restriction filters.
Low static pressure can also indicate a problem. Low pressure could indicate a leaking duct or plenum, a missing filter, low fan speed, or a cut duct.
The Opportunity
The answer to improving static pressure is often outside the box (gears). Static pressure allows you to ‘see’ your system in a whole new light. Airflow becomes visible.
As a result of measuring the static pressure, sewerage restoration work can be prescribed. You begin to realize that your duct system promotes comfort and efficiency. Only when the channels are working correctly can we be sure that the whole system is working properly. Equipment is just one component of the system.
Anyone who sells high-efficiency equipment thinks it stands out from the competition. It’s not. A highly efficient device he has been using for over 30 years.
The new frontier is the canal system.
In terms of value, a properly installed, tested, and balanced duct system is worth far more than a new furnace. What makes us different from our competitors? Our ability to design, install and balance duct systems differentiates us from our competitors.
Static pressure measurement opens the door to the whole system. Many pipe repair and refurbishment jobs are accessible from our daily system. The profit margins are very high, and the skills required for sewer repair are minimal.