The duct blaster is used to quantify the leakage rate of the duct system.
Required 3rd Party Test for New Homes and Retrofits
According to building codes in the state of Illinois, a duct pressure test must be performed if any portion of the HVAC system is placed in unconditioned spaces such as an attic, crawlspace, or garage. The 2012 International Energy Conservation Code is the current version of the energy code and is adopted across the entire state of Illinois for all municipalities and counties. Testing is required to be performed by an independent 3rd party. The code applies when constructing new homes or in a retrofit situation when the duct system has been fully ducted meaning that no building cavities have been used as a return path.
Why is Duct Tightness Important?
- Because indoor air travels through duct work that is prone to leak, placing ducts in areas that are outside the conditioned space can result in a loss of conditioned air to the “outdoors.” Studies show that a typical duct installation loses 20 to 30% of the air before getting to the registers. If that air happens to leak outside the building envelope, comfort complaints and high utility bills will likely result in callbacks.
- Ducts located outside the conditioned space of the home can pressurize or depressurize the building when the air handler is operating which results in increased air leakage through the building envelope.
- Duct pressures can bring pollutants into the indoor air from areas like attics or crawlspaces. These pressures can even interfere with the venting of natural draft water heaters and furnaces.
- Within the home itself, unbalanced air flow from duct leakage can pressurize or depressurize zones in the home and cause comfort complaints.
When Can the Test Be Performed?
You may select one of the following stages of construction to perform your test and still meet the conditions of the energy code.
- Rough-in—with no air handler installed.
- Rough-in—with the air handler installed.
- Post-construction—with no air handler installed.
- Post-construction—with the air handler installed
If you have never had your system pressure tested before to meet the 2012 IECC, the VERY best time to perform the test is at rough-in so that any necessary corrections can be made while there is still access to all of the ducts.
How is the Duct Pressure Test Performed?
- Using a special duct mask tape, the system is temporarily sealed off at all supplies and returns. Note: at the rough-in stage, registers and grilles do not need to be installed to perform the test.
- Using the Minneapolis Duct Blaster from the Energy Conservatory (link to this site removed until they repair their hacked site), we will hook up the fan at the air handler. If the air handler is not yet installed, we will test the supply and return sides of the system independently and add the 2 leakage totals together to determine the total leakage.
- The total amount of leakage in the system is determined by pressurizing or depressurizing the system with the Duct Blaster to 25 pascals (which is equal to 0.1 inches of water column).
What is Considered a Pass or a Fail?
The threshold for passing the test is determined by a certain number of CFM of leakage per 100 square foot of conditioned space that the system serves.
- 3 CFM per 100 SF – Rough-in—with no air handler installed.
- 4 CFM per 100 SF – Rough-in—with the air handler installed.
- 3 CFM per 100 SF – Post-construction—with no air handler installed.
- 4 CFM per 100 Sf – Post-construction—with the air handler installed
The total leakage allowed will vary from system to system. For example, a 2 story house has two systems installed, and the top floor system has duct work running through the attic. The system in the basement is fully in conditioned space. Therefore, only the top system needs to be tested. To determine the allowable leakage, we first must determine the total square footage of conditioned space that the system serves for the house. If the test is performed at the rough-in stage and there is 1200 square feet of conditioned space on the top floor, then the code calls for 3 CFM per 100 SF or a total leakage allowed of 36 CFM.
What if the System Does Not Pass?
Our goal is to help make the process go as quickly and as painless as possible. If the system does not immediately pass the test, our consultants will perform a number of subsequent tests to help isolate the location of the leaks. The installation contractor can immediately make the corrections, and we can immediately verify the results while we are still on site.
Tips for Preparing for the Duct Pressure Test:
- If this is your first test, always have it performed at the rough-in stage so that issues can be easily addressed.
- Sealants
- Based on our experience, systems that use duct mastic pass more readily than those that just use foil tape.
- Apply mastic “as thick as a nickel.”
- If there is an opening more than 1/4″, fasten mesh tape as a backer for the mastic.
- Never use common duct tape on duct work.
- Seal all joints and seams in the system including collar connections, take-offs, and boots.
- Seal all seams at the air handler including the removable pan at the bottom of the blower cabinet.
- Seal the connection of the boot to the subfloor with caulk or mastic.
- If using flex duct, do not rely on a zip tie to provide a seal that can potentially crimp the duct and cause leaks. Apply mastic over the transition, then pull the inner liner over the mastic, then mechanically fasten the liner with screws, pull the fiberglass back over the liner, and then use a zip tie over the fiberglass. Also use this method when a sheet metal sleeve is used to join 2 pieces of flex duct.
- Don’t forget to seal the filter slot. Consider using sheet metal with a gasket or a magnetic filter slot cover such as one found here.
When Will I Receive My Report?
Generally, we will prepare and mail your test results within 24 hours of completion of the test. If time is an issue, we can make other arrangements to suit your needs.
