Retrotec DucTester 300, Operation Manual

Page: 70 / 89

Page 70 of 89
©Retrotec 2017
To field check the DucTester calibration
1. Tape the Field Calibration Plate to the Flex Duct Flange, and attach the blue tube to the pressure
pickup (or into the small cut hole if using a homemade one).
2. Install Range 74 Flow Plug and set same Range on the Gauge.
3. Attach the Flex Duct to the outlet side of the fan to pressurize the Flex Duct. If depressurizing ducts
normally, you can also check the DucTester in that direction by attaching the flex to the inlet of the
fan where you must connect the green reference tube.
4. Stretch the Flex Duct to its full length. Set the “ Mode ” to “Flow” .
5. Press
[Set Pressure] [25] [Set]
and the fan will automatically control to 25 Pa. Press
[@]
to
display “ CFM @25 Pa ” .
6. Compare the measured results with the flow marked on the calibration plate. A homemade plate
with the specified size hole should read within 5% of 105 CFM.
The calibrated fan and flex duct has now been checked as a system, removing that major source of
error.
Figure 44: DucTester field calibration check setup.
Avoid common mistakes
The following mistakes are commonly made when performing a duct test, and can significantly affect
the results.
•
Wrong Range Configuration and or wrong Device selected on gauge
•
Water in tube, pinched tube
•
No green reference tube attached while depressurizing ducts
•
Having @ Pressure on when setting the pressure on the DucTester to zero when measuring duct
leakage to outdoors using method #2.
•
Not covering all registers
•
Not locating and sealing ducts running to outdoors such as fresh air supply ducts
•
Tape sealing registers being blown off, usually
happens in pressurization
•
Furnace coming on during a test
•
Too leaky to test accurately, although this is usually not an issue because tests can be performed
accurately at twice the allowable duct leakage.
•
Be aware of ducts with no leaks:
In some cases, especially in new construction, it is possible to find ducts that have no leaks. Some
indications would be if even a very low fan speed results in a very high duct pressure, or if no flow can
be measured with even the most restrictive Range Configuration. One way to verify that the test is