What You'll Learn

• Where to place manometer probes on a furnace with an A/C coil vs a standalone air handler
• Why the measurement locations differ between equipment types
• How to find the rated maximum TESP on equipment data plates
• What "internal" vs "external" static pressure means and why you measure external
• Common mistakes that produce inaccurate TESP readings
• How measureQuick handles both configurations

What You'll Need

• Device: iPhone (iOS 15+) or Android phone (Android 10+) with measureQuick installed
• Account: measureQuick account with active subscription
• Manometer probes: Paired with measureQuick via Bluetooth (Fieldpiece JL3KM2, UEi DPM, CPS, Testo Smart Probes, or Yellow Jacket YJACK MANO)
• Static pressure tips and tubing: For drilling test ports if none exist
• Understanding of: TESP fundamentals (E9), basic static pressure measurement
• Time: 15-20 minutes for measurement on either equipment type

The Principle Is the Same

Total External Static Pressure measures the total pressure drop that the blower must overcome to push air through the duct system. The formula does not change between a furnace and an air handler:

TESP = |Return Static Pressure| + |Supply Static Pressure|

What changes is where you place the probes because the internal components are arranged differently.

The word "external" is critical. You are measuring the resistance outside the blower section, not inside it. The probes go in the return duct (before the blower) and the supply duct (after all internal components). Everything between those two points - the blower, heat exchanger, evaporator coil, filter (if internal) - is what the blower is working against.

Furnace with A/C Coil

A furnace-based system typically has a gas furnace as the air handler, with an evaporator (A/C) coil installed on top (upflow), on the bottom (downflow), or on the side (horizontal). The furnace contains the blower, heat exchanger, and controls. The evaporator coil is a separate component added to the furnace's supply plenum.

Measurement Points: Furnace

Return side measurement:

• Drill or access the test port in the return plenum or return duct, between the filter and the blower inlet.
• If the filter is in a remote filter rack (not at the furnace), measure between the filter rack and the blower.
• If the filter is at the furnace in a built-in filter slot, measure upstream of the furnace (between the return duct and the filter).
• This reading will be negative (the blower pulls air through the return).

Supply side measurement:

• Drill or access the test port in the supply plenum, after the evaporator coil.
• On an upflow furnace with an A-coil on top: the supply probe goes above the evaporator coil, in the supply plenum or the first section of supply duct.
• On a downflow furnace with a coil below: the supply probe goes below the evaporator coil.
• On a horizontal furnace: the supply probe goes downstream of the coil on the discharge side.
• This reading will be positive (the blower pushes air through the supply).

The key point for furnaces: the supply probe must be after the evaporator coil, not between the furnace and the coil. The evaporator coil is an internal component that the blower must push air through. If you measure between the furnace heat exchanger and the evaporator coil, you are not capturing the coil's pressure drop, and your TESP will be artificially low.

Diagram showing upflow furnace with A-coil, return probe location between filter and blower, supply probe location above the evaporator coil in the supply plenum

Finding the Rated TESP: Furnace

The rated maximum TESP is on the furnace's data plate or in the installation manual. For most standard residential furnaces, this is 0.5 inWC. As shown in the gas furnace workflow video, Jim Bergmann points out: "there's your 0.5 inches total external static pressure - you factory test it so it's at half an inch total external static pressure."

The data plate is usually inside the blower compartment door or on the side panel. Look for a line that says "Maximum External Static Pressure" or "Max ESP" or "Rated TESP." Some manufacturers list it as "External Static - Heating" and "External Static - Cooling" separately, because the evaporator coil adds resistance in cooling mode that is not present in heating-only mode.

If the furnace lists separate heating and cooling TESP ratings, use the cooling rating when the A/C is running (it will be the lower of the two, because the coil adds resistance).

Air Handler (Cooling Only or Heat Pump)

A standalone air handler contains the blower, evaporator coil, and sometimes electric heat strips, all in one cabinet. There is no separate heat exchanger. Air enters the return side, passes through the filter (if internal), across the blower, through the evaporator coil, and out the supply side.

Measurement Points: Air Handler

Return side measurement:

• Drill or access the test port in the return plenum or return duct, between the filter and the air handler cabinet.
• If the filter is inside the air handler, measure upstream of the entire cabinet in the return duct.
• This reading will be negative.

Supply side measurement:

• Drill or access the test port in the supply plenum, after the air handler's discharge.
• The probe goes in the supply duct immediately after the air handler, downstream of the coil.
• On most air handlers, the supply connection is at the top (upflow) or bottom (downflow). Place the probe in the supply duct after that connection.
• This reading will be positive.

Because the evaporator coil is inside the air handler cabinet, you do not need to worry about measuring between the blower and the coil. The supply probe goes after the entire air handler, capturing all internal pressure drops.

[Diagram] Air handler TESP probe placement: the return-side probe goes in the return duct before the air handler inlet (upstream of the unit, reading negative pressure). The supply-side probe goes in the supply plenum after the air handler discharge (downstream of the unit, reading positive pressure). Because the evaporator coil is inside the air handler cabinet, both the blower and coil pressure drops are captured between these two points. There is no need for a measurement between the blower and coil.

Finding the Rated TESP: Air Handler

Check the air handler's data plate (usually inside the access panel) or the installation manual. Air handlers often have a higher rated TESP than furnaces, because they may be designed for use with longer duct runs or multi-zone systems. Values of 0.5", 0.7", or 0.8" are common.

Some variable-speed air handlers have performance tables that show CFM delivery at different static pressure values rather than a single maximum. In that case, the rated TESP is the highest value on the performance table at the desired CFM.

Side-by-Side Comparison

Common Mistakes

Measuring inside the cabinet instead of external static

The most frequent error. "External" means outside the equipment cabinet. If you drill a test port into the furnace's blower compartment or into the air handler's internal plenum, you are measuring internal pressure, not external static. Your reading will not match the equipment's rated TESP, and the measurement is not diagnostically useful for evaluating the duct system.

Probes go in the ductwork attached to the equipment, not inside the equipment itself.

Measuring between the furnace and the evaporator coil

On a furnace-based system, some technicians place the supply probe in the space between the top of the furnace and the bottom of the evaporator coil. This misses the coil's pressure drop entirely. On a system with a dirty coil adding 0.2" of resistance, your TESP measurement would be 0.2" lower than actual. You would think the system is fine when it is not.

The supply probe must be after the evaporator coil, in the supply plenum or supply trunk.

Not accounting for the filter location

If the filter is in a remote filter grille (at a wall return, for example), and you place the return probe between the filter grille and the furnace, your return static reading includes the duct resistance but not the filter resistance. To capture filter drop as part of TESP, measure before the filter (upstream) for return static.

For a four-point static pressure test (measuring at return, after filter, before coil, and supply), you get component-level detail. But for TESP, you need just two points: before the blower (return side) and after all components (supply side). See TESP Budget & 140% Rule for the four-point approach.

Confusing heating-mode TESP with cooling-mode TESP

In heating mode on a furnace without A/C running, the evaporator coil still creates some resistance (the air still passes through it), but the measurement conditions differ. Some furnace data plates list separate TESP ratings for heating and cooling. Use the appropriate rating for the mode you are testing. measureQuick accounts for this in the workflow when you select the test type.

How measureQuick Handles Both Configurations

When you start a project and profile the system, measureQuick asks you to identify the equipment type. Selecting "furnace" or "air handler" affects:

• The diagnostic screen layout and which measurement fields appear
• The rated TESP that measureQuick uses for pass/fail evaluation (based on your profile entry)
• The workflow prompts that guide you through measurement steps, including probe placement reminders

In both cases, measureQuick reads your paired manometer data in real time and calculates TESP automatically from the return and supply readings. The pass/fail evaluation compares the calculated TESP against the rated maximum you entered during profiling.

The gas furnace workflow in measureQuick specifically prompts for static pressure measurement as part of the commissioning process. The static pressure screening quick test also works for both equipment types and guides you through the four measurement positions.

Video Walkthrough

• YouTube: - Complete gas furnace workflow demonstration showing probe placement at return and supply positions around a furnace with an A/C coil. Demonstrates finding the 0.5" TESP on the data plate and capturing manometer readings

• YouTube: (39 min, 3,389 views) - Static pressure workflow inside measureQuick, covering probe placement for different equipment configurations

• YouTube: (358,516 views, 11 min) - Comprehensive walkthrough of static pressure measurement techniques showing measurement point differences between equipment types

• YouTube (HVAC School): (23,171 views, 1:05:15) - Jim Bergmann discusses airflow measurement methodology, including static pressure measurement across different equipment configurations

Tips & Common Issues

I cannot find the rated TESP on the data plate

Some manufacturers do not print TESP on the equipment label, or it may be listed under a different term ("rated ESP," "available static," "maximum external pressure"). If you cannot find it, check the installation manual or the manufacturer's technical data sheets online. For most standard residential furnaces, 0.5 inWC is a safe default. For air handlers, check the performance table in the installation manual.

The furnace has no space between it and the evaporator coil

This is common with cased coils that sit directly on top of upflow furnaces. You may need to drill the test port in the supply trunk or first supply fitting above the coil. The key is that the probe must be downstream of the coil. Even a few inches of duct or plenum above the coil is sufficient for a test port.

Return static is much higher than supply static

This usually indicates a problem on the return side: undersized return duct, restrictive filter, or blocked return grille. On many residential systems, the return side contributes more to high TESP than the supply side because designers often undersize the return. This is the same pattern regardless of whether the air handler is a furnace or standalone unit.

Variable-speed blower adjusts to static pressure

Variable-speed and ECM blowers ramp up motor speed to maintain a target airflow as static pressure increases. This means TESP may not appear as high as it actually is, because the motor compensates. These systems can mask duct problems. If you measure TESP and it appears acceptable but the motor is running at high speed (high watts), the duct system may still be restrictive. Check motor wattage against the manufacturer's rated wattage for the selected airflow setting.

Do I need to measure in both heating and cooling mode?

Ideally, yes. Static pressure differs between modes because heat exchanger and coil components create different resistance. If you are evaluating the system for both heating and cooling, measure TESP in each mode separately. measureQuick records the mode as part of the test so the results are associated with the correct operating condition.

Related Articles

Prerequisites (complete these first):

• Total External Static Pressure - Foundational TESP concepts and measurement
• Manometer Placement: Air Handler - Detailed probe placement for air handlers

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

• TESP Budget & 140% Rule - Breaking TESP into component pressure drops
• Manometer Placement: Furnace - Detailed probe placement for furnace systems

Related in other domains:

• Smart Tool Overview - Compatible manometers and connection methods
• Bluetooth Pairing Basics - Connecting your manometer to measureQuick
• AI System Profiler - Entering equipment information including rated TESP
• Static Pressure Screening - Quick static pressure assessment without a full workflow

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