Retrotec Commercial 441 and 451 DucTester - Manual (Page 34)

Page 34 of 56
©Retrotec Inc. 2015
Table 4-1 Leakage Class
Duct Construction Class ½″, 1″, 2″ wg 3″ wg 4″, 6″, 10″ wg
Seal Class C B A
Sealing applicable Transverse joints only All transverse joints and
longitudinal seams only All transverse joints, longitudinal
seams, and duct to wall penetrations
Leakage Class
Rectangular metal 24 12 6
Round metal 12 6 3
Table 5 Leakage Class
1. Leakage classes in Table 4-1 apply when the designer does not designate other limits and
has specified Seal Class C for ½″ and 1″ wg See text on sealing in the HVAC-DCS manual.
2. Unsealed rectangular metal duct may follow Leakage Class 48.
3. Fibrous glass duct may follow Leakage Class 6 (at 2″ wg or less).
4. Unsealed flexible duct leakage average is estimated to be Class 30. Sealed nonmetal flexible
duct is an average of Class 12.
5. See SMACNA HVAC Duct Systems Design Manual Table 5-1 for longitudinal seam leakage
rates.
6. Although Seal Class A or B might be assigned for lower pressures, the leakage class may not
conform to those associated with the higher pressure. Other construction details influence
results.
7. The duct pressure classification is not the fan static pressure nor the external static pressure
(on an HVAC unit) unless the system designer has made such an assignment in his contract
documents. Unless construction class is otherwise specified it means a static pressure
classification in the SMACNA HVAC-DCS. Those classifications pertain to maximum operating
pressure in the duct as follows:0.5″ wg maximum.
0.6″ to 2″ wg maximum
1.1″ to 2″ wg maximum
2.1″ to 3″ wg maximum
3.1″ to 4″ wg maximum
4.1″ to 6″ wg maximum
6.1″ to 10″ wg maximum
8.2 Leakage Class Calculation
Use the Table in the Section on Leakage Class to determine its value by selecting the pressure value shown under
the flow rate on the X axis (in this example, 2 in WC). Then select the closest Leakage Factor in CFM/100 sq ft as
was observed on the DM32. Where they coincide, is the Leakage Class. Eg. @ Pressure is 2 in WC and Leakage
Factor is 8 then the Leakage Class is 5.1.
You may also use Retrotec FanTestic Software or a calculation spreadsheet. Leakage Class = CL = F (leakage rate in
CFM/ 100 sq ft) divided by the Pressure in in WC to the 0.65 Power. C
L
= F / P 0.65