Retrotec DucTester 341 - Manual (Page 58)

Page 58 of 83
©Retrotec Inc. 2014
12.7 Measure using Hole Flow on the gauge
Because flow through a known size hole depends on pressure across the hole, and air flow into an
enclosed space will cause pressure and flow through the hole, we can use a box with a hole in it to
measure the system air flow.
Cut the flaps off one side of a medium-sized cardboard box. Cut a 2" x 2" square hole in the center of
another side where the cardboard is only one layer thick. Punch a 0.25 inch diameter hole in the box
near the opening and insert a tube into this hole. Connect the other end of the tube to the yellow port
of the gauge (so Channel B is reading the pressure inside the box instead of from the fan). The gauge
should show Pressure on Channel B in Pascals.
Observe the pressure in the box. Increase the size of the hole in the box until the pressure is about 5 Pa.
Box pressure of 8 Pa or less are recommended because higher pressures mean the air handler is
increasingly blocked and the test method itself is affecting the performance.
On the Retrotec gauge, set the device to “HoleFlow”. Enter the area of the hole into the gauge using the
[Area] key, ensuring that the units you use for area match what the gauge is expecting for area. Units
for area when calculating Hole Flow default to square inches. Read the CFM directly from the gauge to
get the air handler flow.
Because this method partially blocks the flow from the air handler, readings are not exact, especially if
pressures in the box are above 8 Pa.
12.8 Measure with a Blower Door attached to the return or cabinet
Measure the supply plenum pressure using the Static Pressure Probe supplied with each Blower Door.
Put the end of the blue tube with the probe into the supply plenum, connect the other end of the blue
tube to the “Input A” (blue) port and read the pressure from Channel A on the gauge.
Attach a 24 inch Flex Duct (optional accessory to Retrotec Blower Doors) to the outlet side of the Blower
Door fan and the Flex Duct flange to a return or the air handler cabinet so it is blowing into the ducts on
the Open Range. Set the pressure to the just measured supply plenum pressure. Press
[Set Pressure]
and enter the previously measured supply plenum pressure. Read the CFM result directly from the
gauge after waiting for at least one minute to let the measurement settle down.
For example, if the pressure in the supply plenum is 70 Pa, press [Set Pressure] , [70] , [Set] to get the
Blower Door to recreate the original pressure in the plenum. Read the CFM result directly from the
gauge
If “---“appears the pressure in the plenum is too high to get an accurate reading. Repeat the procedure
but move the Static Pressure Probe to measure the pressure farther away from the air handler.
12.9 Other methods
Temperature rise and other standard HVAC methods exist but are not covered here.