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© Retrotec 2017
Cannot Reach 50 Pa Factors
Rather than using the equation in the situation where the 50 Pa test pressure cannot be achieved, you can
use tables with the factors already calculated and the following procedure. Take a flow (CFM) reading at
the pressure achieved and multiply by the "Cannot reach 50 factor" from Table 10 to get an estimate of the
flow at 50 Pa.
For example: if you read 1000 CFM at a building pressure of 30 Pa, the "Cannot reach 50 factor" from the table is
1.36. Make the following calculation:
1000 𝐶𝐹𝑀 ×1.39 = 1390 𝐶𝐹𝑀
Thus the estimated result for CFM at 50 Pa will be 1390 CFM.
The factors depend on the “n” value chosen, and
Table 10 i
s for “n” of 0.65 which is typical for houses.
Table 10:
Factors for when a building pressure of 50 Pa cannot be reached (“n” value of 0.65)
Pressure
achieved
Cannot reach
50 factor
Pressure
achieved
Cannot reach
50 factor
50
1.00
25
1.57
49
1.01
24
1.61
48
1.03
23
1.66
47
1.04
22
1.71
46
1.06
21
1.76
45
1.07
20
1.81
44
1.09
19
1.88
43
1.10
18
1.94
42
1.12
17
2.02
41
1.14
16
2.10
40
1.16
15
2.19
39
1.18
14
2.29
38
1.20
13
2.40
37
1.22
12
2.53
36
1.24
11
2.68
35
1.26
10
2.85
34
1.28
9
3.05
33
1.31
8
3.29
32
1.34
7
3.59
31
1.36
6
3.97
30
1.39
5
4.47
29
1.42
28
1.46
27
1.49
26
1.53
