What You'll Learn

• Where to drill test ports on the return plenum and supply plenum for static pressure measurement
• Which manometer port (HIGH vs LOW) connects to which measurement point
• How measureQuick calculates Total External Static Pressure (TESP) from your two readings
• How to zero your manometers before taking measurements
• What the 0.5" wc equipment-rated maximum means and why most systems exceed it
• Which wireless manometers are compatible with measureQuick

What You'll Need

• Device: iPhone (iOS 15+) or Android phone (Android 10+) with measureQuick installed
• Account: measureQuick account with active subscription
• Manometer: One dual-port wireless manometer or two single-port units (see Compatible Tools below)
• Static pressure probes: Two static pressure probes (pitot-style or barbed fittings)
• Tubing: Two lengths of 1/4" ID silicone or vinyl tubing (3-6 feet each)
• Drill and bit: 3/8" drill bit and cordless drill for creating test ports
• Port plugs: Two 3/8" test port plugs or magnetic covers to seal holes when finished
• Knowledge: Understanding of TESP and what it tells you about duct system performance (see Total External Static Pressure)
• Time: 10-15 minutes for first setup; 5 minutes once familiar with the process

The Concept

Static pressure is the force the blower must overcome to push air through the duct system. Measuring it at the air handler tells you whether the duct system is restricting airflow beyond the equipment's rated capacity. You need two measurements: one on the return side and one on the supply side. Together, they give you TESP.

measureQuick calculates TESP automatically when both static pressure readings are present. The formula is straightforward: TESP = |Return static| + |Supply static|. Return static is a negative value (suction), supply static is a positive value (pressure), and TESP is the sum of their absolute values.

From the measureQuick V12 database: more than 70% of tested systems exceed the standard 0.5" wc TESP threshold. Static pressure problems are the most common airflow issue in residential HVAC, and they are invisible without measurement.

Step-by-Step Guide

Step 1: Identify the Two Measurement Points

You need test ports at two specific locations on the air handler.

Return static pressure port:

• Located between the air filter and the blower inlet.
• This measures the pressure drop created by the return duct system and filter.
• On a vertical air handler, this is typically on the side of the return plenum, below the blower compartment.
• On a horizontal air handler or furnace, this is on the return plenum section between the filter rack and the blower housing.

Supply static pressure port:

• Located downstream of the evaporator coil, in the supply plenum.
• This measures the pressure the blower creates to push air through the supply duct system.
• On a vertical unit, this is above the evaporator coil. On a horizontal unit, it is on the downstream side of the coil.

Key rule: Do not place the return port upstream of the filter (that measures filter + return duct combined). Do not place the supply port before the evaporator coil (that misses the coil pressure drop). The goal is to capture the total pressure difference the blower works against.

measureQuick Deploy Indoor Probes instructional diagram showing return and supply static pressure probe positions on an air handler

Step 2: Drill the Test Ports

If the air handler does not already have test ports, you need to create them.

1. Turn off the system. Do not drill into pressurized ductwork with the blower running.
2. Select your drill location. Choose a flat section of sheet metal on the plenum at each measurement point. Avoid seams, corners, and areas near wiring or refrigerant lines.
3. Drill a 3/8" hole at each location. Use a standard 3/8" drill bit. The hole must be large enough to insert your static pressure probe but small enough to seal with a standard test port plug.
4. Deburr the holes. Remove any metal shavings from inside the duct. Loose debris can damage the blower or contaminate the evaporator coil.

Tip: Many technicians leave the test ports in place permanently, sealed with magnetic plugs or foil tape. This makes return visits faster. If the homeowner asks about the holes, explain they are industry-standard diagnostic ports, similar to service valves on the refrigerant lines.

Step 3: Connect the Manometer Tubing

Static pressure manometers have two ports: HIGH and LOW (sometimes labeled + and -, or P1 and P2). The port assignment determines the sign of the reading.

Return side connection:

• Insert a static pressure probe into the return plenum test port.
• Connect tubing from the return probe to the LOW port (negative/minus) of the manometer.
• The return reading will display as a negative value (typically -0.1" to -0.8" wc).

Supply side connection:

• Insert a static pressure probe into the supply plenum test port.
• Connect tubing from the supply probe to the HIGH port (positive/plus) of the manometer.
• The supply reading will display as a positive value (typically +0.1" to +0.5" wc).

If you are using a single dual-port manometer (such as a Fieldpiece JL3KM2, UEi DPM, or Yellow Jacket YJACK MANO), both connections go to the same instrument. If you are using the UEi SPMKIT, it includes two separate manometers, one for each measurement point.

Important: Make sure tubing connections are snug. An air leak at any fitting produces an artificially low reading. Push tubing firmly onto barbed fittings and check that the probe seats tightly in the test port hole.

Manometer with tubing connected to HIGH and LOW ports, with labels showing which tube goes to supply vs return

Step 4: Zero the Manometers

Before starting the blower, zero your manometer(s) with both ports open to atmosphere. This removes any offset from the sensor.

measureQuick includes a "Zero Manometers" step in the guided workflow. When you reach this step during the indoor workflow:

1. Confirm both tubing connections are in place but the blower is OFF.
2. The app prompts you to zero the manometers. Tap Yes to confirm.
3. The manometer transmits its zeroed baseline to the app.

If you are using a standalone manometer (not yet connected to mQ), zero it using the instrument's own zero button before pairing.

Why this matters: A manometer that is not zeroed can be off by 0.01" to 0.05" wc. On a system running 0.45" wc TESP, that error is the difference between a pass and a fail.

[Visual Reference] The Zero Manometers dialog is a centered confirmation popup that appears during the indoor workflow. It reads "Zero Manometers" with instructions to confirm both tubing connections are in place and the blower is OFF. Two buttons appear at the bottom: "Yes" (to proceed with zeroing) and "Cancel." Tapping Yes sends the zero command to the connected manometer, establishing the baseline offset for all subsequent pressure readings.

Step 5: Start the System and Take Readings

1. Turn on the HVAC system. Set the thermostat to call for cooling (or heating, depending on the test mode). The blower must be running at its normal operating speed.
2. Wait 30-60 seconds for airflow to stabilize.
3. Observe the manometer readings streaming into measureQuick on the diagnostic screen.

What you should see:

• Return static: A negative value, typically between -0.1" and -0.8" wc
• Supply static: A positive value, typically between +0.1" and +0.5" wc
• TESP: The sum of the absolute values, calculated by the app

If either reading is 0.00" or very close to zero, check your tubing connections and verify the probe is inserted into the duct (not resting outside the hole). If both readings are zero, verify the blower is actually running.

measureQuick diagnostic screen showing live return static, supply static, and calculated TESP values

Step 6: Evaluate the Results

measureQuick evaluates TESP against the equipment's rated maximum. For most standard residential equipment, the rated maximum is 0.5" wc (inches of water column).

The 140% rule: External static pressure should not exceed 140% of the equipment's rated static pressure. Beyond that threshold, PSC blower motor performance drops significantly. ECM or X13 (constant airflow / constant torque) motors compensate by drawing higher watts, which shortens motor life.

Air handler vs. furnace TESP ratings: On an air handler, the evaporator coil is internal to the unit and already included in the TESP measurement. The only external components are the supply and return duct systems, so air handlers are typically rated at 0.3" to 0.5" wc. Furnaces, by contrast, have the filter and evaporator coil external to the furnace cabinet. The probes must be placed in the cabinet return (post-filter) and below the evaporator coil (pre-coil), meaning the measurement captures more components and furnaces are typically rated at 0.5" wc.

Where does the restriction come from? Common culprits: undersized return duct, dirty or restrictive filter, undersized supply duct, dirty evaporator coil, closed or blocked registers, excessive flex duct runs.

For a deeper breakdown of how TESP fits into duct system evaluation, see Total External Static Pressure and TESP Budget & 140% Rule.

Step 7: Seal the Test Ports

When you are finished measuring:

1. Remove the static pressure probes from the test ports.
2. Insert 3/8" test port plugs, apply magnetic covers, or seal with foil tape.
3. Verify no air is leaking from the sealed ports while the blower is running.

Leaving test ports unsealed introduces duct leakage and can change system performance.

Compatible Manometer Tools

These wireless manometers pair with measureQuick via Bluetooth Low Energy and stream static pressure data directly into the app. For pairing instructions, see Bluetooth Pairing Basics.

Video Walkthrough

• YouTube: (3:54, 12.7K views, 103 likes). Demonstrates pairing a Fieldpiece manometer with measureQuick and setting up static pressure measurement

• YouTube: (1:00, 3.5K views, 57 likes). Quick demonstration of the double-zero technique for manometer accuracy

• YouTube: (0:34, 5.7K views, 95 likes). Common mistake: moving the manometer to a different orientation after zeroing introduces offset error

• YouTube: (8:29, 5.3K views, 114 likes). Detailed walkthrough of zeroing procedures for Fieldpiece manometers

• YouTube: (39 min, 3.4K views). Extended walkthrough covering probe deployment, measurement interpretation, and how to present findings to customers

• YouTube: (358K views, 11 min). Comprehensive demonstration of static pressure testing and duct pressure mapping

• YouTube: (248K views, 33 min). Foundational training on manometer operation, units of measurement, and static pressure theory

Tips & Common Issues

Readings are unstable or fluctuating

Small fluctuations (0.01"-0.02" wc) are normal and caused by blower motor variations and air turbulence. Large swings suggest an air leak in the tubing, a loose probe in the test port, or the probe tip is too close to the blower wheel. Move the test port location if turbulence is excessive.

Return static reads positive instead of negative

The tubing is connected to the wrong port. Swap the HIGH and LOW connections, or reverse the probe assignment in the app. Return static should always be negative (suction side of the blower).

TESP seems too low

Check that the system is operating at normal blower speed. If the thermostat is set to "fan only," the blower may run at a lower speed than it does during a cooling or heating call. Run the measurement with the system in the mode you want to evaluate (cooling call for A/C testing, heating call for furnace testing).

Also check for leaks in the tubing. Even a small leak reduces the measured pressure.

Cannot drill into the plenum

Some air handlers have double-wall construction or internal insulation that makes drilling more difficult. Use a step drill bit for cleaner holes in thicker material. On internally insulated plenums, push the insulation aside after drilling so the probe tip is exposed to the airstream, not buried in insulation.

If the equipment is under warranty and the installer or manufacturer prohibits drilling, document this limitation in the test notes. Some jurisdictions and manufacturers have specific requirements about test port locations.

Only one manometer available

If you have a single dual-port manometer, you can measure both return and supply simultaneously by connecting the LOW port to the return probe and the HIGH port to the supply probe. The manometer displays the differential pressure, which equals TESP directly.

If you have a single single-port manometer, measure return and supply sequentially. Take the return reading first with the blower running, note the value, then disconnect and reconnect to the supply probe. measureQuick accepts both values entered at different times.

Do not reposition the manometer after zeroing

Once you zero the manometer, do not move it to a different orientation (e.g., from flat on a surface to hanging on the side of the air handler). The pressure sensor's zero reference depends on its physical orientation. Changing position after zeroing introduces offset error. Zero the manometer in the position and location where it will remain during the measurement.

Zeroing was skipped or done with blower running

If you zeroed the manometer while the blower was running or while tubing was already pressurized, the baseline is wrong and all readings will be offset. Turn off the blower, disconnect tubing from the probes (or remove probes from the duct), re-zero, reconnect, and re-measure.

Test ports from a previous visit

If the air handler already has test port holes (from your previous visit or another technician), verify they are in the correct locations before reusing them. A port that is upstream of the filter or between the filter and the coil (rather than between the filter and the blower) will produce incorrect readings.

Reference Material

Download: Tests and Probes Quick Reference (PDF)

Related Articles

Prerequisites (complete these first):

• Bluetooth Pairing Basics
• Total External Static Pressure (TESP)

Follow-up articles (next steps after this one):

• TESP Budget & 140% Rule
• Outdoor Probe Placement
• Indoor Probe Placement
• Manometer Placement for Static Pressure (general guide)
• Static Pressure Screening Test
• A/C Service Workflow

Related in the same domain:

• Smart Tool Overview
• TrueFlow Grid Setup
• TrueFlow Airflow Measurement

Need Help?

If you get stuck or this article does not answer your question:

• Check the Related Articles section above
• Watch the video walkthroughs linked above for visual guidance
• Contact measureQuick support: support@measurequick.com