Duct Leakage Testing Requirements in 2021 IECC Codes

Date Published: June 16, 2023

If you are in the building industry, you are no doubt familiar with the International Energy Conservation Code (IECC).  This code is used as an industry standard for new building projects and renovations. And it establishes what guidelines need to be followed in order to meet code. As an Energy Services company, we make it our business to stay in-the-know about any IECC updates or changes. That is why we are going discuss the recent changes to duct leakage testing requirements within the IECC 2021 version.

But before we dive into the IECC changes, let’s first discuss duct leakage testing and what it is…

What is Duct Leakage Testing?

Simply put, the purpose of duct testing is to evaluate how well a home’s duct system can hold air. The more leaks your duct system has, the less efficient it will be.

A leaky duct system will result in wasted energy and wasted money. Furthermore, poorly sealed air ducts can cause unevenly distributed heat or AC throughout the home, resulting in an uncomfortable living environment.

At Scott Energy Services, duct leakage testing is one of our primary energy services. Most counties in Colorado adhere to the IECC standards, and thus, the duct leakage protocol. As a result, we have performed hundreds of these tests with our tried and true method!

duct leakage testing equipment

How Does It Work?

To begin, all duct openings (including supply and return registers) must be sealed off with specialized HVAC tape. A large fan is then sealed securely to the air handler opening or a large return opening (as shown above). However, this is usually done at rough-in on new construction homes.

We run the fan to depressurize the duct system down to -25 pascals. The amount of air moving through the fan is then calculated. This number, referred to as the CFM25, indicates the amount of air leakage in the duct system.

For more details about our duct leakage testing process, you can check out our website.

How Did the IECC 2021 Codes Change Duct Leakage Testing?

Believe it or not, just one sentence was removed from the 2021 IECC duct testing section. However, this one change makes a BIG difference.

If you look at the “exceptions” in the R403.3.3 Duct testing section of the 2018 IECC, it states that “a duct air-leakage test shall not be required where the ducts and air handlers are located entirely within the building thermal envelope.” This is consistent in IECC 2015 codes as well.

The reason this initial exception existed was because if duct leakage occurred within the thermal envelope, heated or cooled air could still be captured to a certain degree.

Now compare that to section R403.3.5 Duct testing in the 2021 IECC, and that statement has been removed. This means that, in jurisdictions that have adopted the 2021 IECC, all air-handling ductwork will need duct testing, even if it does not run outside the thermal envelope of the home. For homes with more than one HVAC system, both systems will need to be tested.

This is big news, and it might be a bit of a curveball for some builders. This is because it has never been a requirement, since the IECC’s inception of the duct testing rule in 2015.

When comparing ductwork that remains within the thermal envelope to ductwork that exits the thermal envelope, leakage requirements differ slightly. According to section R403.3.6, leakage for duct systems that leave the envelope of the home, must not exceed 4.0. cubic feet per minute per 100 square feet of the conditioned floor area. On the contrary, ducts that remain within the thermal envelope must be less than or equal to 8.0 cubic feet per minute per 100 square feet. So there is slight bit more leniency when it comes to ducts within the thermal envelope.

Builders who haven’t needed this type of testing in past projects now must factor it in. They must be sure not to skip over this stage of testing during their projects. It will also contribute to a marginal increase in costs that must be factored where necessary.

What Are the Benefits Of This Change?

This updated code might ruffle some feathers. But from an energy efficiency standpoint, this rule does have its benefits. One of our certified HERS raters, Joe Ophoff, spoke on the matter:

“In new construction home design, there is a great emphasis on air leakage and distribution.  New homes are designed for super performance, so really fine-tuning distribution systems are necessary for comfort throughout the house. Too much duct leakage can indicate a failure in the installation of the duct system, so we can catch a bad install at the ‘rough mechanical’ phase to ensure things are installed correctly. But also, the duct designs are carefully calculated to ensure distribution equilaterally throughout the house, so any significant leakage would affect that.”

Joe illustrates this point well – it all comes down to energy efficiency and optimum HVAC performance. If your interior ducts have too much leakage, they might not evenly distribute heat/air throughout the house. So when you get the system tested during the building process, you are able to pinpoint any issues and have them addressed before the project is finished.

In many counties across the country, including most in Colorado, Manual J/S/D reports are required to get a permit. These reports design the duct system prior to installation; and they calculate the perfect amount and balance of airflow and velocity for each room of the home. However, these reports assume the presence of well-sealed ducts for the results to match the initial calculation.

So this is another step in the process of engineering a super comfortable home for the homeowner, and ensuring everyone is getting the most out of the energy they are using. We wouldn’t be surprised to see actual airflow balancing or velocity testing requirements in the future to even further verify the performance of the duct systems.

In Need of Energy Services?

At Scott Energy Services, a division of Scott Home Services, we are seasoned duct leakage experts. But that’s not all. We also have a number of other energy services, including energy audits, HERS rating, blower door testing, REScheck report services, insulation inspections and air barrier inspections. And we make sure to stay up on the ever-changing codes, in order to help you move along through your project without a hitch.

But what’s a good duct system without the right mechanical design? As you likely know, the IECC requires all new builds and additions to submit a Manual J, S, and D report to ensure mechanical design code compliance. This is another service that we proudly offer. If you need a Manual J/S/D report, we a have team of experts ready to help!

No matter what your next building project needs may be, we would love to be of service! Visit us online to learn more or contact us to book your services today.

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About the Author: Chris Kimmel

Chris Kimmel worked as an Associate Home Inspector for two years, handling numerous services including sewer scope inspections, pest inspections, mold air sample testing, radon testing, and water quality testing. Chris now works with Scott Home Inspection as a Content Writing Specialist.

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