Retrotec Residential Pressure & Air Leakage - Manual (Page 31)

Page 31 of 75
Set the Time Average to 20 seconds on a calm day and one minute on a windy day or even 2 minutes on a very
windy day. This will alleviate the largest source of error and takes less time than performing a multipoint test
with a computer which doesn’t add much more in the way of accuracy. Take test points for at least as long as
the time averaging setting.
4.2.2. Test Duct Leakage to Outdoors by measuring air flow with a Flow Hood
A flow hood can be used to measure the flow going in to or coming out of a register, and can therefore
determine total duct leakage to the outdoors. The house is pressurized or depressurized with all the ducts
sealed and a flow hood on one register. If there is any flow measured at the register, it will be due to the
pressure difference between the house and outdoors through the ducts.
To measure duct leakage with a flow hood
1. Setup the house for a basic air leakage test.
2. Turn off the air handler, and open all registers. Remove all HVAC filters.
3. Seal all combustion appliance air intakes.
4. Seal all ventilation intakes that are connected to the duct system.
5. Seal all supply and return registers, but leave the largest register that is close to the air handler
open.
6. Pressurize the house to 50 Pa (or depressurize to -50 Pa).
7. Place the flow hood over the open register. Record the flow. The measured flow is an estimate of
the total duct leakage to the outdoors.
Most flow hoods are capable of measuring airflow in both directions, and the house can be pressurized or
depressurized. Make sure to follow the manufacturer's guidelines for proper operation of the flow hood.
4.2.3. Check the pressures in unconditioned spaces to avoid errors in Leakage to
Outdoors measurement
When estimating duct leakage to the outdoors with any of the methods described above, it is important to make
sure that unconditioned spaces that contain ductwork have a balanced pressure with the outdoors. The
estimate of duct leakage to the outdoors will be inaccurate if the unconditioned spaces become partially
pressurized during the test. One way to verify that the unconditioned spaces have an equal pressure balance is
to conduct a simple zone test on the unconditioned spaces.
To check the zone pressure in unconditioned spaces