What You'll Learn

• Where to drill static pressure test ports on a furnace with an A-coil, and why the heat exchanger changes the placement compared to an air handler
• How to position the return-side port between the filter and blower
• How to position the supply-side port between the heat exchanger outlet and coil inlet, and after the coil
• How to connect a manometer for gas manifold pressure measurement
• How to read equipment-specific rated TESP from the furnace data plate
• Which Bluetooth manometers are compatible with measureQuick and their key specs

What You'll Need

• Device: iPhone (iOS 15+) or Android phone/tablet (Android 10+) with measureQuick installed
• Account: measureQuick account with active subscription
• Bluetooth manometer: One of the compatible manometers listed below, paired with measureQuick
• Drill: 3/8" drill bit for test ports (metal or sheet metal bit for furnace cabinets)
• Static pressure tips: Stainless steel static pressure probes with magnetic bases
• Tubing: Silicone or rubber tubing to connect probes to the manometer
• Plugs or caps: To seal test ports when not in use
• Access to the furnace: Both the blower compartment and the supply plenum above the coil
• Time: 10 minutes to read; 15 minutes to drill ports and set up manometers in the field

Why Furnace Placement Differs from Air Handler

On an air handler, the blower pulls air through the filter and pushes it directly through the evaporator coil. There are two measurement zones: return side (before blower) and supply side (after coil).

On an upflow furnace with an A-coil on top, the heat exchanger sits between the blower and the evaporator coil. This creates three measurement zones:

1. Return side: Between the filter and the blower (same as air handler)
2. Mid-point: Between the heat exchanger outlet and the coil inlet (furnace-specific)
3. Supply side: After the evaporator coil (same principle as air handler, different physical location)

The mid-point zone does not exist on an air handler. It is unique to furnace installations and is valuable for isolating heat exchanger pressure drop from coil pressure drop when building a TESP budget (see E11).

Cross-section diagram of upflow furnace with A-coil showing three pressure measurement zones - supply, return after filter, and draw-through

Test Port Locations

Port 1: Return Side (Between Filter and Blower)

Location: Drill a 3/8" hole in the furnace cabinet or return duct between the filter rack and the blower compartment. On most upflow furnaces, this is on the side of the cabinet below the blower, after the filter but before air enters the blower wheel.

What it measures: Return-side static pressure. This is the negative pressure created by the blower pulling air through the filter and return ductwork.

How to connect: Insert a static pressure tip into the drilled hole. The tip should extend about 1 inch into the airstream, pointing perpendicular to the airflow (not into the flow and not with the flow). Connect the tip to the manometer's negative (-) or low port with tubing.

Expected range: -0.10 to -0.40 inWC on a typical residential system. More negative values indicate higher restriction on the return side.

Static pressure tip installed in a 3/8 inch test port on the return side of an upflow furnace cabinet, between the filter and blower

Port 2: Mid-Point (Between Heat Exchanger and Coil)

Location: At the top of the furnace cabinet, between the furnace outlet and the A-coil inlet. On an upflow furnace, this is the transition piece between the furnace and the coil casing. Some furnace installations have a sheet metal plenum or adapter between the furnace and the coil where a test port can be drilled.

What it measures: Pressure at the point where air has passed through the heat exchanger but has not yet entered the evaporator coil. This reading, combined with the return-side reading and the supply-side reading, lets you calculate:

• Heat exchanger pressure drop = (mid-point pressure) - (return pressure) - (blower contribution)
• Coil pressure drop = (mid-point pressure) - (supply pressure)

When to use this port: For TESP budget analysis (E11) and component-level pressure drop isolation. This port is not required for the standard TESP measurement, which uses only Port 1 and Port 3.

How to connect: Insert a static pressure tip into the drilled hole. Connect to a separate manometer channel or swap the tubing from Port 3 after taking the standard TESP reading.

As noted in the gas furnace workflow, the technician places "one up here that's below the evaporator coil that's measuring my supply-side static" - in some field setups this mid-point location serves as the supply reading when no separate port exists above the coil.

Static pressure tip installed in the transition between furnace top and A-coil bottom

Port 3: Supply Side (After Evaporator Coil)

Location: In the supply plenum above the A-coil. Drill a 3/8" hole in the supply plenum or trunk duct, above the evaporator coil casing.

What it measures: Supply-side static pressure. This is the positive pressure created by the blower pushing air through the heat exchanger and evaporator coil into the supply ductwork. Combined with Port 1 (return side), this gives you TESP.

How to connect: Insert a static pressure tip into the drilled hole. Connect the tip to the manometer's positive (+) or high port with tubing.

Expected range: +0.10 to +0.40 inWC on a typical residential system. Higher values indicate greater restriction on the supply side.

Calculating TESP: TESP = |Return static| + |Supply static|. For example: return = -0.25, supply = +0.35, TESP = 0.25 + 0.35 = 0.60 inWC.

Upflow furnace cross-section showing airflow path with labeled measurement points at Return, After Filter, and Before Coil

Gas Manifold Pressure Connection

Gas manifold pressure is not a static pressure measurement in the ductwork sense, but it uses the same manometer instrument and the same basic technique.

Where to Connect

The gas valve on the furnace has a manifold pressure tap - a 1/8" NPT fitting on the downstream side of the valve. It is typically capped or plugged from the factory.

1. Remove the cap or plug from the manifold pressure tap
2. Connect a short length of tubing from the tap to the manometer's positive (+) port
3. Leave the manometer's negative (-) port open to atmosphere
4. The manometer reads manifold pressure as a differential above atmospheric

Reading and Evaluating

The furnace data plate specifies the required manifold pressure. Standard values:

• Natural gas: 3.5 inWC (most common)
• LP/Propane: 10-11 inWC (most common)

Always check the specific furnace data plate. Some furnaces specify different values, and two-stage furnaces may have different manifold pressures for low fire and high fire. The gas furnace workflow profile captures these values: "60,000 BTU input, 42 on the low side, the temperature split is 15 to 45 degrees... the maximum gas supply pressure is seven, the minimum is five, and 3.5" manifold.

If measured manifold pressure does not match the data plate spec, the gas valve's regulator requires adjustment. This is outside the scope of this article but is covered in the gas furnace workflow (G4).

Equipment-Specific Rated TESP

Every furnace has a rated maximum Total External Static Pressure printed on the data plate or in the installation manual. This is the maximum external pressure drop the blower is designed to overcome while delivering rated airflow.

Where to find it: Look for "Maximum External Static Pressure," "Rated ESP," or "External SP" on the furnace data plate. It is usually expressed in inches of water column (inWC).

Typical values:

• Standard 80% furnace: 0.50 inWC
• High-efficiency 90%+ furnace: 0.50-0.80 inWC (varies by model and blower type)
• Variable-speed ECM blower: 0.50-0.80 inWC (higher-rated TESP due to the ECM's ability to ramp up to overcome resistance, but this increases energy consumption)

As stated in the workflow: the furnace data plate shows "your 0.5 inches total external static pressure - you factory test it so it's at half an inch total external static pressure."

Using the rated TESP:

• If measured TESP is at or below the rated maximum: Pass. The system is operating within design parameters.
• If measured TESP exceeds the rated maximum: Fail. The system is restricted. Use the 140% rule and TESP budget (E11) to identify the cause.
• If measured TESP exceeds 140% of the rated maximum: Ductwork is the dominant restriction.

measureQuick compares your measured TESP to the rated maximum from the system profile and assigns pass/fail automatically.

Compatible Bluetooth Manometers

The following Bluetooth manometers integrate with measureQuick for static pressure and gas pressure measurement. Any of these will work for the furnace measurements described in this article.

Fieldpiece JL3KM2

• Type: Dual-port manometer (part of the JobLink system)
• Connection: Direct Bluetooth Low Energy
• Key feature: High-accuracy differential measurement
• Wireless range: 1,000+ feet
• Battery: AAA, 150 hours
• Part of kit: Included in the Fieldpiece JobLink JL3KH6 Complete Kit ($1,022.99)

UEi DPM Wireless Differential Pressure Manometer

• Type: Standalone dual-port manometer
• Connection: Direct Bluetooth Low Energy
• Range: +/-80 inWC
• Accuracy: +/-0.03 inWC (at 3 inWC)
• Resolution: 0.01 inWC
• Features: Zero function, magnetic mount, auto power off
• Use case: Static pressure testing and gas pressure verification

UEi SPMKIT Wireless Static Pressure Kit

• Type: Complete kit with two manometers
• Connection: Direct Bluetooth Low Energy
• Range: +/-80 inWG per manometer
• Accuracy: +/-0.03 inWG (at 3 inWG)
• Kit contents: 2 SPM manometers, 2 static pressure probes, 2 stepped T fittings, tubing, brass fittings, carrying case
• Key advantage: Two manometers for simultaneous supply and return measurement without moving probes

CPS SPM-K1 Static Pressure Meter

• Type: Manometer with 5 built-in test modes
• Connection: Direct Bluetooth Low Energy (BLE Smart)
• Range: +/-75 inWC
• Resolution: 0.004 inWC
• Accuracy: 0.04 inWC typical
• Price: $130.43
• Kit contents: Manometer, two 6-foot tubes, brass gas manifold fitting, color-coded stainless steel probes with magnetic bases
• Key advantage: Budget-friendly at $130 with excellent accuracy. Includes gas manifold fitting for furnace work.

Testo 510i Differential Pressure Probe

• Type: Part of the Testo Smart Probes system
• Connection: Direct Bluetooth Low Energy
• Wireless range: 350 feet
• Battery life: 150 hours
• Part of kit: Included in the Testo Smart Probes Complete Kit ($1,423.49, which includes 2x 510i probes)

Yellow Jacket YJACK MANO (67068)

• Type: Wireless dual-port manometer
• Connection: Direct Bluetooth Low Energy (BLE 4.2)
• Price: $233.32
• Wireless range: 400 feet line-of-sight
• Part of ecosystem: Works with YJACK VIEW App and measureQuick simultaneously

[Visual Reference] Five wireless manometers are compatible with measureQuick for static pressure measurement:

• Fieldpiece JL3KM2 - Dual-port, JobLink BLE, $190.99
• UEi SPMKIT - Dual-port, Direct BLE, $217.31 (includes tubing and static pressure tips)
• CPS SPM-K1 - Dual-port, Direct BLE, $165.00
• Testo 510i - Differential pressure, Direct BLE, $159.00 (also available as part of the Smart Probes Complete Kit)
• Yellow Jacket YJACK MANO (67068) - Dual-port, Direct BLE, $233.32, 400-foot range

Measurement Workflow

Step 1: Zero the Manometer

Before connecting to test ports, zero the manometer with both ports open to atmosphere. Leave the manometer in its measurement position and orientation while zeroing. As the measureQuick short video emphasizes: "Stop repositioning your manometer after zeroing." Moving it after zeroing can introduce positional offset.

Some manometers (like the RetroTech precision manometer covered in training events) support auto-zeroing. For others, use the manual zero button.

Step 2: Connect Return Side

Connect the return-side static pressure tip to the manometer's negative/low port. Verify you see a negative pressure reading when the blower is running.

Step 3: Connect Supply Side

Connect the supply-side static pressure tip to the manometer's positive/high port. If using a single-port manometer, take the return reading first, record it, then move the tubing to the supply port.

If using the UEi SPMKIT (two manometers), connect one to return and one to supply for simultaneous measurement.

Step 4: Read TESP in measureQuick

With both connections active, measureQuick calculates TESP as the sum of absolute values. The app compares to the rated maximum from the system profile and displays pass/fail.

Step 5: Gas Manifold Pressure (If Applicable)

Switch the manometer to the gas manifold connection. Connect tubing from the manifold pressure tap to the positive port. Read manifold pressure and compare to the data plate spec.

measureQuick static pressure measurement screen showing return, supply, and TESP with pass/fail indicator

Video Walkthrough

• Stop repositioning your manometer after zeroing (0:34, 5.7K views): - Why you should not move the manometer after zeroing, and how positional offset affects readings

• Double-zero your manometers (1:00, 3.5K views): - Proper zeroing technique for accurate static pressure readings

• Zeroing Fieldpiece Manometers (8:29, 5.3K views): - Complete Fieldpiece manometer zeroing walkthrough

• Fieldpiece Manometers and measureQuick (3:54, 12.7K views): - How to pair and use Fieldpiece manometers with measureQuick for static pressure measurement

• measureQuick Gas Furnace or Boiler Workflow 2022 (31 min): - Complete gas furnace workflow showing manometer placement for return static, supply static, and manifold pressure. Shows the full probe setup on a furnace with A-coil

• Tuning a Gas Furnace with Testo Smart Probes and the BluFlame Analyzer (19 min, 10K views): - Furnace testing with Testo Smart Probes (including 510i manometers) and BluFlame combustion analyzer

Tips & Common Issues

I only have one manometer

Take the return-side reading first. Record the value (or use measureQuick's hold function). Disconnect the tubing and reconnect to the supply-side test port. Record the supply reading. measureQuick calculates TESP from both values. The UEi SPMKIT solves this by providing two manometers in a single kit.

The test port hole is too large or leaks

If the drilled hole is larger than the static pressure tip, use a rubber grommet or a short section of tubing with a tight fit to seal the gap. Any air leak at the test port reduces the accuracy of the reading. After testing, cap the hole with a 3/8" plug or a dab of silicone sealant to prevent air leakage during normal operation.

Static pressure readings seem too low

Verify the blower is running at the correct speed. If the blower is on a low speed (common in fan-only or intermittent operation), the static pressure will be lower than at full cooling or heating speed. Take static pressure readings during active cooling or heating operation, not during fan-only mode.

Supply static reads negative instead of positive

The manometer ports may be reversed. Return side connects to the negative/low port; supply side connects to the positive/high port. If both are negative, the supply-side tip may be in the return airstream, or the tubing connections are swapped.

Manifold pressure drifts during measurement

Minor fluctuations (0.1-0.2 inWC) in manifold pressure are normal due to gas regulator behavior. If the pressure fluctuates more than 0.5 inWC, the gas regulator may be malfunctioning, or the supply pressure to the building may be unstable.

ECM blowers compensate for high static

Variable-speed ECM blowers ramp up motor speed to maintain target airflow as static pressure increases. This means TESP on an ECM system may read closer to the rated maximum even when the ductwork is undersized, because the blower is working harder to push air through. The system "passes" TESP but at the cost of increased energy consumption and noise. Check the blower wattage against rated values to see if the motor is working harder than it should.

Drilling into the furnace cabinet vs. ductwork

For return-side ports on furnaces where the return duct connects directly to the cabinet, drill into the duct rather than the furnace cabinet if possible. Drilling into the cabinet risks hitting internal components. If you must drill into the cabinet, verify the location is clear of wiring, gas lines, and the heat exchanger before drilling.

Reference Material

Download: Tests and Probes Quick Reference (PDF)

Related Articles

Prerequisites (complete these first):

• Manometer Placement: Air Handler - General manometer placement principles for air handlers
• Total External Static Pressure - TESP measurement technique and interpretation

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

• TESP Budget & 140% Rule - How to break TESP into component pressure drops using the mid-point port
• Combustion Probe Placement - Where to insert the combustion analyzer flue probe
• Gas Furnace Workflow - Complete guided workflow for gas furnace testing

Related in the same domain:

• Indoor Probe Placement: Furnace - Temperature and pipe clamp placement on furnaces
• Outdoor Probe Placement - Outdoor probe positions for the condensing unit
• Static Pressure Measurement - General static pressure measurement technique

Need Help?

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

• Check the Related Articles section above
• Contact measureQuick support: support@measurequick.com