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©Retrotec 2017
New duct systems must leak less than 6% of the air handler’s flow.
Maximum allowable duct tester measurement based on 3 different base system air handler flow is:
For A/C systems multiply the Tonnage X 24 CFM.
Assumes 400 CFM per Ton with maximum allowable leakage
of 6% = 24 CFM per Ton.
TONNAGE ___ X 24 = _____
CFM
E.g. a 5 Ton system must have less than 5 X 24 = 120 CFM of leakage at a 25 Pa test pressure in the
supplies.
For Heating systems divide the BTU /1000 X 1.302 CFM.
Assumes 21.7 CFM per 1000 BTU capacity with maximum
allowable leakage of 6% = 1.302 CFM per 1000 BTU.
BTU _________ /1000 X 1.302 =
____CFM
E.g. a 100,000 BTU furnace must less than 100,000 / 1000 X 1.302 = 132 CFM of leakage.
Measure the fan flow divided by 100 X 6.
Measured fan flow ______ / 100 X 6 =
____CFM
E.g. an air-handler blower flow of 2000 CFM must have less than 2000 / 100 X 6 = 120 CFM of
leakage.
Existing duct systems must leak less than 15% of the air handler’s flow.
The Maximum allowable duct tester measurement based on 3 different base system air handler flow is:
For A/C systems multiply the Tonnage X 60 CFM.
Assumes 400 CFM per Ton with maximum allowable leakage of 15% = 60
CFM per Ton.
TONNAGE ___ X 60 = _____
CFM
E.g. a 5 Ton system must have less than 5 X 60 = 300 CFM of leakage at a 25 Pa test pressure in the supplies.
For Heating systems divide the BTU /1000 X 3.255 CFM.
Assumes 21.7 CFM per 1000 BTU capacity with maximum allowable leakage
of 15% = 1.302 CFM per 1000 BTU.
BTU _________ /1000 X 3.255 =
____CFM
E.g. a 100,000 BTU furnace must have less than 100,000 / 1000 X 3.255 = 326 CFM of leakage.
Measure the fan flow divided by 100 X 15.
Measured fan flow ______ / 100 X 15 =
____CFM
E.g. an air-handler blower flow of 2000 CFM must have less than 2000 / 100 X 15 = 300 CFM of leakage.
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