Duct Leakage Testing in Colorado. Who, What, Where, When, How?

Date Published: January 3, 2024

At the time of this writing, most Colorado counties have adopted the 2018 IECC 0r the 2021 IECC. These energy standards have established that a number of field tests are required to validate the energy performance of a home. This includes blower door testing and duct leakage testing – both are important tests for evaluating residential energy efficiency. In this article, we will take a closer look at duct leakage testing in Colorado.

IECC Duct Leakage Requirements

When it comes to duct leakage testing, the 2018 and 2021 IECC rules are very similar, save for one key difference. In the 2018 IECC, Duct leakage testing is not required on any part of the duct system that is located within the thermal envelope of the building. This rule is consistent with the 2015 IECC. On the other hand, according to section 403.3.6 item #3 of the 2021 IECC, now all ducts must be tested – even if they are within the thermal envelope.

For more information about the 2021 IECC duct leakage code updates, check out our article, Duct Leakage Testing Requirements in 2021 IECC Codes

Testing is required to be performed by an independent third party. The code applies to new home construction and remodels/additions in some municipalities. These rules will vary from county to county, based on what IECC version has been adopted. So its always a good idea to check with the local building department to see what is required.

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
  • 8 CFM per 100 Sf – Post-construction—with the air handler installed and all ducts within the conditioned envelope (2021 IECC)

duct leakage testing equipment

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.

Scott Home Services

At Scott Energy Services, a division of Scott Home Services, we have a team of highly trained energy efficiency and air leakage specialists. We offer an extensive list energy services including Duct Leakage Testing, Blower Door Testing, HERS Ratings and more! So whatever your building requirements may be, we are here to be of service.

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

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About the Author: Chris Scott

Chris Scott is an ASHI certified home inspector with multiple years of experience in home inspections, blower door testing, duct leakage testing, and Boulder Rental License Inspections. Chris is also the Website Coordinator for Scott Home Inspection.

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