Retrotec Residential Pressure & Air Leakage - Manual (Page 45)

Page 45 of 75
8. Increase the size of the flow measuring hole in the box until the pressure is between 2 and 8 Pa.
9. Look up the Exhaust Flow in Table 7 based on the pressure in the box (from “PrA”) and the final
area of the flow measuring hole.
10. If you have a Retrotec gauge, it can calculate the exhaust fan flow for you.
a. Set the “Mode” to “Hole Flow”.
b. Enter the area of the hole into the gauge using the
[Area] key.
c. Read the Exhaust Flow in CFM directly from the gauge on Channel B, “Hole Flow”.
Tip: Box pressure of 8 Pa or less is recommended because higher pressures will decrease the exhaust fan flow
rate. Box pressures below 3 Pa are less accurate because small fluctuations in pressure will affect the flow a lot.
Try the same fan with different holes to see the different results.
Table 8: Determine exhaust fan flow in CFM (grey cells) with a known hole size under known pressure conditions.
Exhaust
Flow
(CFM)
Hole Size (sq in)
4 5 6 8 10 12 14 16 18 20 25 30 35 40 45 50 55 60 65 70
Pr
e
ssur
e
(
Pa
)
1
4 5 6 9 11 13 15 17 19 22 27 32 38 43 48 54 59 65 70 75
2
5 7 8 11 13 16 18 21 24 26 33 40 46 53 59 66 72 79 86 92
2
6 8 9 12 15 18 21 24 27 30 38 46 53 61 68 76 84 91 99 106
3
7 9 11 15 19 22 26 30 34 37 47 56 65 75 84 93 102 112 121 130
4
9 11 13 17 22 26 30 34 39 43 54 65 75 86 97 108 118 129 140 151
5
10 12 14 19 24 29 34 38 43 48 60 72 84 96 108 120 132 144 156 168
6
11 13 16 21 26 32 37 42 47 53 66 79 92 105 119 132 145 158 171 184
7
11 14 17 23 28 34 40 46 51 57 71 85 100 114 128 142 157 171 185 199
8
12 15 18 24 30 37 43 49 55 61 76 91 106 122 137 152 167 183 198 213
9
13 16 19 26 32 39 45 52 58 65 81 97 113 129 145 161 177 194 210 226
10
14 17 20 27 34 41 48 54 61 68 85 102 119 136 153 170 187 204 221 238
11
14 18 21 29 36 43 50 57 64 71 89 107 125 143 161 178 196 214 232 250
5.2.6. Use a pre-built Exhaust Fan Flow Meter instead of building your own box
There are pre-built meters available, which are just a box with a hole in it of a known size as described in the
previous section on “Create an Exhaust Fan Flow Meter”. If you wish to use a manufactured box with a hole in it
such as the “Exhaust Fan Flow Meter” built by The Energy Conservatory, you can measure the pressure in the
flow meter box on any channel of the gauge and look up the flow in the manufacturer’s table reproduced in this
document. You can also use the “Hole Flow” Mode on the Retrotec gauge to do the calculation and read the
result directly from the gauge as described in the previous instructions.
The Retrotec DM32 works directly with the “Exhaust Fan Flow Meter”. Connect the Meter to Channel B.
Do NOT use the Device titled “Mn Exhaust Fan” on your DM-2 gauge because it has a cut-off at 10 Pa and the
maximum pressure for the Mn Device is 8 Pa, meaning it won’t work in its range. Above 10 Pa, this Mode should
work fine but the procedure outlined below will always work.