Retrotec Residential Pressure & Air Leakage User Manual
Page 30
Page 30 of 75
©Retrotec Inc. 2014
Table 6: Correction factors for duct pressure
Duct Pressure
Subtraction
Correction Factor
Duct Pressure
Subtraction
Correction Factor
11
6.71
31
2.14
12
6.12
32
2.06
13
5.63
33
1.98
14
5.20
34
1.91
15
4.83
35
1.84
16
4.51
36
1.78
17
4.23
37
1.71
18
3.97
38
1.65
19
3.74
39
1.60
20
3.54
40
1.54
21
3.35
41
1.49
22
3.18
42
1.44
23
3.03
43
1.39
24
2.89
44
1.34
25
2.76
45
1.29
26
2.64
46
1.24
27
2.52
47
1.19
28
2.42
48
1.14
29
2.32
49
1.09
30
2.23
50
1.00
To get duct leakage to a more commonly used 25 Pa, multiply the result by 0.64. Alternatively, set the pressure
to 50 Pa for the test but use the “@25Pa” feature to estimate the flow at the desired test pressure. You must
still correct this result using the Subtraction Correction Factor.
Example: Whole House leakage is 2200 CFM50; Envelope leakage with ducts sealed off is 2100 CFM50 the duct pressure is 39 Pa giving a correction
factor of 1.60. Calculate as follows: 2200-2100 = 100 x 1.60 = 160 which means the ducts leak 160 CFM at 50 Pa. For duct leakage at
25 Pa which is required by most Codes, Multiply 160 X 0.64 = 102 CFM
Improve the accuracy and ease of testing by pressurizing and other methods
Pressurize instead of depressurizing the house because the tape will not be blown off the registers. Retrotec
1000 and 2000 fans don’t require any changes when pressurizing so long as the red tube is connected to the red
port the gauge will show the positive pressure and correct automatically but other fan makes require a
reference tube be attached between the gauge and outdoors on Channel B (this step is usually missed)
otherwise huge error will result. Most Codes require testing in the opposite direction (depressurization) for
house leakage measurement which means another test should be performed in that direction for house leakage
although both results should be very similar.
Use the @50 Pa or @25 Pa feature on the gauge depending on at what pressure you want results. Take the
house test pressure up to 50 Pa for both tests but the gauge will display the reading at exactly the pressure you
need which will eliminate the inaccuracy of needing to get the test pressure exactly right.