Duct Leakage Testing - SUPPLY SYSTEM

To perform a proper duct leakage test using an ORIFLOW duct leakage tester, perform the following

  1. Use the orifice plate with the recommended leakage range for your job. Use our online
    program to help determine which plate(s) you can use with our testers.
  2. Make sure you have adequate electrical power for the fan. DO NOT OVERLOAD extension
    cords. Make sure you use one with the proper gauge.  
  3. Cover all outlets with plastic bags and seal with duct tape.
  4. Allow all joints and seams that were sealed with duct sealer to cure for at least 24 hours or the
    required cure time by the manufacturer, whichever is greater.
  5. If possible, position the ORIFLOW duct leakage tester in a location where there will be a
    straight path from the orifice tube outlet to the location where you will feed air into the system.
  6. Drill a 3/8" diameter hole no closer than two or three feet away from the flexible duct to system
  7. Place the pressure tubing into the previously drilled hole; extend 6 to 12 inches into the duct.
  8. Seal the tubing penetration joint with putty or tape.
  9. Zero both gauges. Locate adjusting screw on center front of gauge. Use a small slotted
    screwdriver. Turning clockwise increases the pressure reading, counter-clockwise decreases
  10. Close the fan's inlet damper so the duct system does not get overpressurized by the tester.
  11. Turn on the tester blower.
  12. Adjust inlet damper until the reading on the gauge marked "Duct System" is at the system
    pressure required for performing the leakage test.
  13. Once the duct system pressure has been reached and stabilized, note the reading on the
    gauge marked "Orifice Tube". This pressure drop reading will correspond to the amount of air
    you're feeding into the duct system, which is the amount of air that is leaking out.
  14. Refer to the calibration table that came with your test rig. Find the pressure reading and note
    the corresponding leakage rate.


If the "Orifice Tube" gauge exceeds the maximum range, the system is probably leaking too much air.
Investigate system for missed outlets or unsealed joints. You can also use a larger orifice or a gauge
with a larger range.

If you cannot obtain any pressure (or very little pressure) with the blower on and the inlet damper wide
open, it could be due to one of the following problems:

    1. Using too small of an orifice plate
    If pressure drop across orifice plate is more than 2 in.wg., use the next greater sized
    orifice plate.  Use our online program to determine which orifice plate you should use
    based on the maximum allowable leakage. You can also refer to graphs for each
    tester/plate combination.

    2. System has more leakage at test pressure than is allowed
    When using the Cobra or Lynx tester, use the 4-inch plate to pressurize your system
    and refer to the following table to determine if your system is leaking more than the
    maximum capacity of the tester.

    Also check your flex-duct connections Wrap duct tape tightly around the joint and feel
    for leaks. Rectangular duct joint corners can be typical leaky points.  If fire damper
    and/or heater coils are part of the system you are testing, they also can be significant
    leak contributors. A smoke machine may be used to help locate leaks; contact us for
    more information.

    3. Equipment not working properly
    Make sure the equipment is working properly by doing the following steps:
  • turn off blower.
  • observe blower wheel rotation direction when it slows down (view from looking
    through inlet safety screen); it should be rotating clockwise (if not, contact us).
  • completely close inlet damper.
  • disconnect the flex-duct from the tester.
  • turn on blower.
  • Slowly open inlet damper and verify that you can feel air coming out of the orifice
  • the orifice tube gauge pressure drop reading should be maxed out.
  • you can verify gauges are working properly by removing pressure tubing and
    carefully apply pressure by gently blowing into tube end as if trying to inflate a
Copyright 2014 All rights reserved, ORIFLOW LLC
Maximum Leakage Capacity (cfm)*
1 in.wg.
2 in.wg.
4 in.wg.
6 in.wg.
8 in.wg.
10 in.wg.
12 in.wg.
14 in.wg.
16 in.wg.
550 cfm
540 cfm
455 cfm
230 cfm
655 cfm
645 cfm
600 cfm
465 cfm
200 cfm
1350 cfm
1320 cfm
1210 cfm
1065 cfm
875 cfm
615 cfm
270 cfm
1630 cfm
1550 cfm
1420 cfm
1330 cfm
1185 cfm
1035 cfm
895 cfm
660 cfm
480 cfm
Maximum Leakage Capacity (L/s)*
250 Pa
500 Pa
1000 Pa
1500 Pa
2000 Pa
2500 Pa
3000 Pa
3500 Pa
4000 Pa
260 L/s
255 L/s
215 L/s
110 L/s
310 L/s
305 L/s
285 L/s
220 L/s
95 L/s
640 L/s
625 L/s
570 L/s
505 L/s
415 L/s
290 L/s
130 L/s
770 L/s
730 L/s
670 L/s
630 L/s
560 L/s
490 L/s
425 L/s
310 L/s
230 L/s
* - Using the largest size orifice plate. Note each tester comes with one plate. Other orifice plate sizes are available for accurate testing
of different flow ranges. Use smaller orifices for smaller flow ranges; largest orifice for maximum flow range..