The IECC-2012/2015 code requires field testing to validate the energy performance of the home. This has most recently included blower door testing and duct leakage testing. Duct leakage testing is required by many cities and counties in Colorado when any part of the duct system is outside the heated envelope or thermal boundary.

At Scott Home Inspection, we have a team of energy efficiency and air leakage specialists that can do the testing to help you meet your building requirements and have the results back to you in a timely manner.

Independent Assessment

In Colorado, a duct leakage test must be performed if any portion of the HVAC system is placed in unconditioned spaces such as an attic, crawlspace, or garage. Testing is required to be performed by an independent third party. The code applies to new home construction and remodels/additions in some municipalities. This rule is enforced by specific cities and counties so check with the local building department to see if they require it. The list is growing larger every day.

The Purpose of Duct Leakage Testing:

  • Studies show that a typical duct installation loses up to 20% of the air before getting to the registers. If that air happens to leak outside the building envelope, the overall comfort of a home can be compromised, and high utility bills will likely ensue.
  • When air is blowing through ducts outside the conditioned space of the home, this can cause a change in pressure between the heated and unheated areas. This can lead to more air movement between the two areas which will transfer heat/cool air outside of the home.
  • Leaks in ducts can pull in air from these unconditioned areas. High pressure in an attic, for example, can push dirty or dusty air into the home through small gaps in the ceiling.
  • Within the home itself, unbalanced air flow caused by duct leakage can pressurize or depressurize zones causing rooms to be stuffy or to have temperature variation.

When is the best time to do a duct leakage test?

Duct leakage testing can be done during various stages of construction and still meet the specifications of the energy code, although we recommend performing it at rough-in when access is easiest. This also gives you the ability to seal sections of the ducts while they are still exposed.

How do we perform the test?

We use the “Duct Blaster” to test the air supply and quantify leakage. We seal off all the registers in the home and run a fan at a return, or at the air handler to depressurize the system. The total amount of leakage in the system is determined by pressurizing or depressurizing the system with the Duct Blaster to 25 pascals.

Click here to view a great article about duct leakage tests from the air leakage pioneers, The Energy Conservatory.

What Comprises 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. Here are the baseline numbers given in the IECC 2015 codes.

  • 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

Helpful hints to pass your Duct Leakage Test:

  • If this is your first test, always have it performed at the rough-in stage so that issues can be easily addressed.
  • Liquid Mastic or “pookie” has shown the best results based on our experience.
  • Seal every joint. The test is very sensitive, so the HVAC professional may need to seal quite a bit more than normal.
  • The furnace or air handler is often overlooked. Seal around the edges and around the back side of the handler where the returns connect.
  • Flex duct is popular in attics. However, the zip ties conjoining them to the system have a tendency to leak. Add mastic to these joints as well to create a tight seal.
  • Make sure the filter cover is fully installed and sealed before the test.
  • Do a once over of the full system before the test to identify weak or unfinished areas.
  • It can be helpful for the HVAC installer to be present during the inspection to help identify and repair leaks on the spot.

For more information or to schedule a duct leakage test with Scott Home Inspection, click here.