Retrotec DucTester 341 - Manual (Page 65)

Page 65 of 83
©Retrotec Inc. 2014
15. 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
correct, and that the ducts are not leaky, is to unseal a single register. This introduces a leak to the duct
system, which is measured by the equipment. If this test results in a measure leak of the approximate
size of the opened register, the previous test is valid, and the system is too tight to measure any duct
leakage.

Method 2 duct leakage to outdoors or combined method has erratic readings:
Huge errors will result if the @ Pressure function is turned on during this test because it creates a divide
by zero error. Press [@] to remove “@” from under the result. This method relies on the DucTester
gauge measuring the pressure between the house and ducts which is set to zero by the DucTester but
the extrapolation to zero that is attempted by the gauge will not work.