Retrotec DucTester 200 Series Residential Applications - Manual (Page 10)

Page 10 of 91
©Retrotec Inc. 2015
1.1.1. Range Configurations
Figure 2: Three flow rings: Low, Mid and Open, restrict flow through the fan inlet.
All Retrotec calibrated fans have multiple Range Configurations in order to measure a wider range of air
leakage flows. During testing, it is necessary to select the correct Range Configuration to achieve
measurable and accurate results.
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 725 CFM.
The Model 200 has three Range Configurations: Low, Mid, and Open. When adding restriction plates, it
is important that they always be installed on the fan inlet. In order to work correctly, the plates must
restrict the airflow as it enters the fan. Restricting the outflow has no effect on the inlet pressure.
When depressurizing, the Flex Duct must be removed in order to change the plates.