Retrotec DucTester 341 - Manual (Page 43)

Page 43 of 83
©Retrotec Inc. 2014
If the target pressure has been reached, but “--“appears as a flow reading, the fan is running too slowly
to measure flow. Perform the following to get a duct leakage result:
1. Add the next smaller Range Ring.
2. Change Range Configuration on the gauge to match the Range Ring installed on the fan.
3. Re-adjust DucTester fan speed.
If the Range Ring installed is the smallest hole, there are no more Range Rings to install, and “--“still
appears:
1. Make sure Range Configuration on the gauge actually matches the installed Range Ring.
2. Check that the blue tube is connected to the gauge and then check that it is reading pressure – put a
finger on the open end of the blue tube and ensure that the Channel A pressure reading changes. If it
does not, then the tube is blocked or pinched.
3. Check that there is no blockage in the ducts between the DucTester and the register containing the
blue tube. To do this, move the blue tube to a different register and compare the reading on Channel
A to the original reading. If the pressures in the two locations are not similar, there may be blockage
in the duct system that needs to be removed.
4. Check that the DucTester is actually reading properly on Channel B. To do this, open up a taped
register to provide enough leakage to get a reading, and then increase the pressure to 25 Pa or 50 Pa
on Channel A. If the flow still reads “--” then the yellow or green tubes could be blocked or
disconnected.
If you are sure that the blue tube is reading pressure, there is no blockage in the ducts or tubes, and that
the DucTester is actually reading flow, and “--“ still appears, the ducts must be extremely tight; less
than 7 CFM. To get a rough result, cover half the inlet ring with tape which will quadruple the fan
pressure signal. Read the CFM, but divide the answer by two (since half the hole is open). If still reading
“--”, cover three quarters of the inlet with tape, read the CFM and divide the answer by four (since only
one quarter of the hole is open).
Instead of doing the calculations, an alternative is to set the Result to be Displayed” to “Pressure:
Pa”and look up the associated flow in Table 9 (for 25 Pa induced duct pressure).
8.6 Cannot achieve test pressure
If the DucTester fan reaches 100% speed on the “Range 74” Range Ring before reaching the target
pressure, the fan is not providing enough air flow to reach the target pressure. Perform the following to
reach the target pressure:
1. Remove a Range Ring.
2. Change Range Configuration setting on the gauge to match the fan.
3. Re-adjust DucTester fan speed.
If there is no Range Ring installed (i.e., “Open” with no more Range Rings to remove), and the desired
test pressure cannot be reached at maximum speed:
4. If the duct pressure is close to the required test pressure (within 5 Pa), use the [@] key to extrapolate
to what the flow would be at the desired pressure.
5. Try the Duct Leakage to Outdoors test, which will neutralize duct leakage to the house.
6. Look for large disconnects in the duct system by pressurizing the house with the Blower Door and
putting smoke in front of the registers. Registers with high velocity smoke movement are a good
indication of a potential disconnect behind that register. Fixing the disconnect in the ducts may
reduce the leakage enough to continue testing the duct system.