airflow_trueflow (V12)The TrueFlow Grid is a calibrated pressure-averaging plate. It replaces the air filter temporarily during a test, and the pressure drop across it correlates directly to airflow volume.
When air moves through any restriction, a pressure difference develops across it. A narrow restriction produces a larger pressure drop for a given airflow; a wider restriction produces a smaller drop. This relationship between pressure and airflow is predictable and repeatable if the restriction geometry is known and consistent.
The TrueFlow Grid contains multiple sensing ports distributed across its surface. These ports feed into a single pressure channel on the TEC DG-1000 (or DG-8), producing an average pressure reading across the entire grid face. The TEC TrueFlow App receives this pressure value and converts it to CFM using the grid's factory-calibrated resistance characteristics for the selected adapter plate size.
This is the same measurement principle used in blower doors and duct testers: measure pressure across a known opening, convert to flow.
As Jim Bergmann describes it: "I personally really love the true flow plate - true flow plate gives you a bunch of different sizes, typically... it does a duct traverse for you and it actually measures it out in total pressure."
The TrueFlow Grid does not connect directly to measureQuick. The data path is:
TrueFlow Grid --> DG-1000 (via BLE) --> TEC TrueFlow App --> measureQuick (App-to-App)
The DG-1000 reads the raw pressure differential. The TEC TrueFlow App performs the pressure-to-CFM conversion. measureQuick receives the calculated CFM value through an App-to-App transfer. Both apps must run on the same phone.
| Spec | Value |
|---|---|
| Flow range | 300-2,500 CFM |
| Flow accuracy | +/-5% |
| Battery | 24+ hours (2,000 mAh Li-ion, USB-C charging) |
| Connectivity | Bluetooth Low Energy, USB 2.0 |
| Grid dimensions | 12 x 18 x 0.75 inches |
| Weight | 2.1 lbs |
| Operating temperature | 32F to 115F |
| Calibration interval | 48 months |
| Connection type | App-to-App (TEC TrueFlow App to measureQuick) |
| Price range | $617.00 (grid + 1 adapter) to $2,162.00 (full kit with DG-8) |
Pressure gauges drift. Temperature changes, altitude, and electrical noise all cause the baseline reading to shift away from true zero. If the DG-1000 reads 0.02" WC when no pressure is applied, that offset carries through every measurement. On a 0.30" WC reading, a 0.02" offset is nearly 7% error, which exceeds the grid's +/-5% accuracy spec and renders the measurement unreliable.
The DG-1000 auto-zeros itself at regular intervals. You will hear a click when it re-zeros. Unlike Fieldpiece manometers, you do not need to manually zero the DG-1000 before each reading. The auto-zero cycle disconnects the pressure channel momentarily, reads the zero-pressure baseline, and corrects for any drift.
However, there is a practical consideration: the auto-zero cycle can occur during a measurement. If it happens while you are capturing a reading, the DG-1000 briefly shows zero before returning to the actual value. Wait for the reading to restabilize after an auto-zero event before recording. The 5-second stabilization window applies here.
If you relocate the DG-1000 to a different elevation (moving from a basement to an attic, for example), the barometric pressure change can exceed the auto-zero correction range. Manually re-zero the gauge at the new location before taking readings.
The temperature-split (enthalpy) method estimates airflow from supply and return air temperatures, wet bulb readings, and system capacity. measureQuick uses this when no direct measurement is available. It is a calculation, not a measurement.
The enthalpy method has three significant error sources:
TrueFlow measures actual air volume passing through a calibrated restriction. It does not depend on temperature readings, capacity assumptions, or the condition of the refrigerant circuit.
Fan curve matching uses the manufacturer's published airflow table for a given blower motor speed and static pressure. You measure the static pressure, look up the blower speed setting, and read the expected CFM from the table.
This method assumes the fan curves are accurate, the blower wheel is clean, and the motor is delivering its rated performance. A dirty blower wheel, a failing capacitor, or an aging ECM motor can all reduce actual airflow below the published curve without changing the static pressure reading.
TrueFlow measures the airflow directly, regardless of blower condition.
A capture hood (such as the CPS EasyHood ABM-200 or Testo 420) measures airflow at individual supply or return registers. To get total system airflow, you sum all the register readings. This is accurate but time-consuming on systems with many registers.
TrueFlow measures total system airflow in one reading at the main return filter slot. On systems with a single return, TrueFlow is faster and equally accurate (+/-5%).
The TrueFlow Grid relies on the adapter plate creating a complete seal across the filter opening. If the adapter plate is smaller than the opening, air bypasses the grid and the reading is low. If the adapter plate is larger, it cannot seat properly.
The grid ships with 8 adapter plate sizes covering standard filter openings from 14x20 to 25x25. Measure the opening before selecting the adapter plate. Guessing the size is the most common source of measurement error.
Any air bypassing the grid produces a low reading. Run your hand around the grid perimeter while the blower runs. If you feel air escaping, reposition the grid and press firmly against all four edges. For rough or uneven duct openings, use blue painter's tape, foam weatherstrip, or cardboard shims to seal the gap.
Joe Medosch covers this in the San Jacinto College training: keep some sealing material in your TrueFlow bag for non-standard openings. The grid must cover the opening completely.
Systems with angled filter slots (where the filter sits at a diagonal) present a problem. The TrueFlow Grid does not measure accurately in angled orientations because airflow distributes unevenly across the grid surface, creating a dead spot on one side and concentrated flow on the other. Place the grid at the bottom of the slot where it can sit flat, or use an alternative measurement point.
On ECM or constant-torque blower motors, the motor may ramp up when it senses the added restriction of the TrueFlow Grid. Run the system in high speed or high stage during TrueFlow measurements. If the system is in auto mode, the motor may compensate and produce readings that do not reflect normal operating airflow. PSC motors do not adjust speed in response to restriction.
When TrueFlow airflow data enters measureQuick through the App-to-App connection, the system records it distinctly from other airflow sources:
airflow_source = "trueflow" - identifies this as a direct TrueFlow measurementairflow_trueflow - stores the measured CFM value in a dedicated V12 columnTests with airflow_source = "trueflow" produce the most reliable diagnostic outputs in measureQuick. The Vitals Score weights measured airflow higher than estimated airflow. Superheat, subcooling, and capacity calculations are all more accurate when they use measured rather than estimated CFM.
Tests tagged "estimated" or "manual" are useful but carry wider uncertainty. If you have a TrueFlow Grid, use it. The diagnostic accuracy it provides pays for itself by catching duct problems that estimated airflow masks.
YouTube: (10:47) - Complete TrueFlow-to-measureQuick data flow including grid setup, DG-1000 connection, and App-to-App transfer
YouTube (HVAC School): (1:05:15, 23,171 views) - Jim Bergmann discusses airflow measurement methods including the TrueFlow Grid in context of static pressure and capacity testing
YouTube: - Jim Bergmann explains the enthalpy method for airflow estimation and why measured airflow (TrueFlow) is preferred
YouTube: (1:27:15, 1,663 views) - Includes TrueFlow report demonstration on an existing system and discusses available static pressure, airflow options, and sensible heat factor
Check the grid seal first. Air leaks around the perimeter are the most common cause. Then verify the blower is running at the correct speed. If the system has multiple return grilles and you are measuring only one, total airflow is the sum of all returns.
Check temperature probe placement for the estimated airflow. If the supply probe is too close to the register face, it reads mixed air, which inflates the estimated airflow. Also verify the system profile tonnage is correct, since an incorrect tonnage changes the enthalpy-based estimate.
Wait at least 5-10 seconds after placing the grid. Close interior doors near the return to reduce pressure fluctuation. Check for exterior wind effects on the ductwork, and verify that no other return grilles are partially blocked.
If the return grille opening exceeds 25x25 inches, a single TrueFlow Grid cannot cover it. If the filter slot is angled, the grid cannot seat properly. In these cases, use a capture hood at individual registers, or fall back to the enthalpy-based estimate.
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