Retrotec DucTester 341 - Manual (Page 18)

Page 18 of 83
©Retrotec Inc. 2014
5.1.1. Range Configurations
Open 74 47 29
Figure 3: Open Range is for the leakiest ducts and houses while Ranges 74, 47, 29 are for progressively tighter ducts.
All Retrotec calibrated fans have multiple Range Configurations in order to measure a wider range of air
leakage flow rates. Select the correct Range Configuration by running the fan speed up to ensure it is
running at over 50% speed and the gauge is giving a flow result. If not change to a lower range and
repeat.
A calibrated fan measures flow by measuring the pressure developed inside the fan, which is often
called Fan Pressure. As the fan speeds up, a suction pressure develops at the inlet of the fan that causes
air to flow. By measuring this Fan Pressure, airflow can be calculated using pre-determined flow curves
or tables, or the Retrotec gauge, which applies the same calculations automatically and displays the
Flow directly.
When the fan slows down, the Fan Pressure can become too small to accurately measure. To increase
the Fan Pressure, a restriction plate is placed in front of the fan. The fan, consequently, has to turn
faster to maintain the same room or duct pressure, which creates a larger, more accurate Fan Pressure.
By providing a set of flow restricting plates with calibrated holes, Retrotec DucTester fans can measure
flows from 7 CFM to 800 CFM.
The Model 300 has 4 standard Range Configurations: Open, 74, 47and 29 as standard. Open range is
accessed by removing the cover over the fan inlet called End Plate 300. The numbered Ranges are 4
inch Plugs that snap into the End Plate and will restrict the flow to allow you to measure lower flow
rates. The numbers refer to the approximate hole diameter in millimeters. Most residential ducts in new
comes can be tested using Range 47. Older existing houses can be tested using Range 74 and super tight
ducts on Range 29.
When depressurizing, the Flex Duct must be removed in order to change the Ranges.
CFM
minimum
CFM
maximum
Range
name
Included
91 802 Open
45 199 74
15 78 47
2.7 32 29
2.6 12 18 optional