Retrotec Residential Pressure & Air Leakage - Manual (Page 43)

Page 43 of 75
5.2 Pressure Balancing and Performance Testing
5.2.1. Pressure Imbalances can be Due to Forced Air Systems
Air handlers typically move from 500 to 2000 CFM of air. When their supply and return flows are not in balance,
the building itself can be subject to pressure imbalances. This can increase air infiltration rates, and cause
susceptibility to radon and moisture entry, combustion appliance spillage, and backdrafting. A pressure
imbalance of as low as 2 Pa can cause back drafting. It is important to understand how a home’s HVAC system
contributes to the comfort and safety of the occupants.
Pressure imbalances can also be caused by duct leakage to the outdoors, and are exacerbated when the air
handler/exhaust fans are on. If there are leaks in the supply duct, the building can suffer depressurization.
Depressurization, even by 1 Pa, can lead to severe moisture problems in warm humid climates where infiltrating
air carries high volumes of moisture. Infiltrating air will contact cooler surfaces (i.e. backside of gypsum board),
reach the dew point and condense. Over time, this can create building integrity issues. When the leaks are in
the return duct, the building will tend towards pressurization. When supply and return leaks are equivalent in
size, the positive and negative pressures balance out. However this is not often the case.
The following is a set of diagnostic test procedures to help find pressure imbalances caused by leaks in the duct
system. Note that these tests are sensitive to wind fluctuations so must be performed under calm conditions.
5.2.2. Run a Dominant Duct Leakage Test
This test will measure the depressurization or pressurization of the building caused by duct leakage to the
outdoors while the air handler fan is running.
1. Close all exterior doors and windows, and open all interior doors.
2. Replace (cleaned) HVAC filters. Make sure the air handler and exhaust fans are off.
3. Connect the red tube to the “Ref A” (red) port on the gauge and send it outside. Keep the “Input A”
(blue) port open to the building.
4. Take a Baseline on the gauge to zero out any existing bias pressures in the building.
5. Record the air handler OFF pressure from “PrA”
6. Turn on the air handler fan (or exhaust fan) and record the air handler ON pressure
7. Calculate the pressure difference between ON and OFF readings.
Repeat this test several times for more accuracy in your results.
The results can indicate the following:

Consistent positive pressures indicate a leaky return duct system

Consistent negative results suggest a leaky supply duct system

The magnitude of the pressure reading will depend on the amount of imbalance and the tightness of the
building being tested

No change in building pressure indicates that there is either equal supply and return leakage to the
outside, no leaks to the outside, or the building is too leaky for the duct leakage to create a measurable
pressure change
5.2.3. See if rooms with Closed Doors get pressurized by air handler running
The master bedroom is often the largest room in the home and can contain several supply registers, but no
return registers. Measuring the effect of closing the bedroom door on the pressure in the main part of the
house can determine whether or not the bedroom is becoming pressurized during air handler activity, while
other parts of the home are being depressurized. This test can be repeated for other rooms in the building that
have registers, and can be closed off from the main body of the house.