What is a duct leakage test?

ByAllen Czermak


Ryan is a friend of mine who is quite good with his hands. Last summer he helped me build a deck for my backyard in just two weeks. It took two whole weekends to complete the installation which included cutting, measuring, and drilling. He and I did a fantastic job and Ryan wanted to know if I could help him out with something of his own. You see Ryan had purchased an abandoned home that was on foreclosure for just $225,000. He planned on flipping the home and selling it after it was renovated. Since it had not been lived in for over five years, the home attracted strangers who used it as a shelter. Every time it was boarded up by the local code enforcement, these individuals would manage to pry their way in. All this activity over the course of time took a toll on the home’s infrastructure and Ryan would have to gut the house and do a complete renovation prior to putting it up on the market for resale.

After a year and a half of work, the home was finally looking nice. With a brand-new kitchen, chic laminate flooring, updated appliances, plush carpeting, a new roof, and many other renovations, the home looked like new. Ryan was now ready to list the house on the market for $295,000. During the restoration process, he made sure that the HVAC system was in working order. The thermostat was replaced, air ducts were cleaned, and filters were replaced. After reviewing the work, which was done, he asked me if I knew of any home inspectors to make sure all was in order. I looked through my contacts and found Steve, a home inspector who I had used when we were purchasing our new home.

Later that week, Steve came down to the newly renovated home and was truly amazed with Ryan’s handiwork. The inspector began to run the heat and then the air conditioner to see if they were in working order. He then asked Ryan for the duct leakage test report. Ryan was a bit perplexed and responded, “Excuse me, but what is a duct leakage test?”. Steve was a bit surprised that Ryan had never heard of an air duct leakage test and Steve gave him a number to call a local NJ specialist who can find air leaks in a house. The guy came down, setup the equipment, and ran the duct blaster test. The report was then sent to the home inspector and Ryan was able to list the property at $295,000 which sold at $290,000

Does my new home or property really need to have duct pressure testing?

According to International Energy Conservation Code any time there is construction with a new a new HVAC system, a duct leakage test must be done to receive a Certificate of Occupancy (CCO). This means that you are obligated to conduct a duct leakage test and deliver a report to the builder or building inspector for code compliance. It’s not the piece of paper that’s important but it’s the information which is on the report. You need to pass the code max allowance of duct leakage which is 8 CFM per every 100 square feet. The area which is measured is the area which is conditioned by the heating and cooling system. This means that the square footage of a basement must be included in the test. Say your home is 3,200 square feet of conditioned space, your CFM allowance would be 3200 / 100 = 32 x 8 = 256 of max CFM. Anything greater than that will require you to identify the leaks and seal them up to get you in CFM range needed for compliance.

What in heaven’s name is CFM?

CFM is a unit of volumetric flow which stands for cubic feet per minute. This is a measurement of how much of something is passing through an area of square feet. In the case of a duct leakage test, we want to get an air flow measurement of how much air is escaping the HVAC system. Now according to code compliance, every home or business is allowed up to 8 CFM to escape. Anything greater than that would be non-compliant and deemed not energy efficient according to The American Recovery and Reinvestment Act of 2009. The ARRA was signed into law by the Obama administration and now requires all new construction with a new HVAC system to conduct a duct blaster test and pass to receive a COO.

How long does it take to perform a duct leakage test?

The actual test takes under a minute. It’s the setup which is extremely time consuming. For it to be setup correctly, you need to hire a DET (Duct & Envelope Tightness) Verifier who is certified to perform the test. Doing it yourself or asking a friend to perform is not recommended.

Here is some reason why not to perform a duct leakage test by someone who is not certified:

  • The ducts might not be sealed tight which will allow air to escape, giving you an inaccurate read of CFM.
  • The equipment, which is being used may not be calibrated properly, giving you an inaccurate read of CFM.
  • The calculation of conditioned square footage may be inaccurate which throws the whole test off even before bringing any of the equipment into your home. 
  • In the case where the air duct leakage test is performed correctly and you get a read which is above the max allowance, you still need to find the air leaks in the house and have them sealed properly.

How is a duct leakage test done?

When you have located yourself someone who is certified, they will first begin by making sure all the openings to the air ducts are sealed with temporary register sealing tape. This tape is placed over all the registers and grills in the home leaving only the air handler cabinet exposed. The fan will then have a snorkel that is affixed to the air handler cabinet without any air escaping the face plate. It’s very important to use temporary register sealing tape and not to use duct or gopher tape to avoid damage being done when the tape needs to be removed.

Once the sealing is complete the fan will be turned on which creates a negative pressure in the air ducts. According to the International Energy Conservation Code (IECC), every duct system is tested with 25 pascals (a pascal is a unit of pressure used to quantify internal pressure or stress). At this point, the duct leakage specialist will get a read on their digital pressure gauge of how many CFM is escaping the ducts for the respective conditioned area. Higher than 8 CFM per 100 square feet will require identification of air leaks to have them sealed up.

How to find an air leak in ductwork?

After it’s verified that the duct leakage analysis did not meet compliance, it’s time to find those air leaks in your duct work. This is done by the builder, HVAC installer, or duct leakage professional using a smoke machine. That’s right, the same smoke machine which is used by heavy metal bands will now generate smoke into your air ducts. Another option to generate smoke would be to use fire-less smoke bombs or smoke pellets directed at the fan.

Once there is a significant amount of non-toxic smoke in your ducts it’s now time to inspect the outside of the duct work to determine if there are any air leaks. Since there is smoke in the ducts, one will be able to see if there are any areas where it’s seeping through. Once the leaks are spotted they will be sealed with ac duct sealant and most likely covered by a layer of foil mastic sealant tape. Once it’s confirmed that no more smoke is leaking out of the duct work, the technician will rerun the duct leakage test until a compliant CFM read is computed. Once all is complete, a report will be given to you showing the results.

How much duct leakage test cost?

It depends on how big the tested space is and how long the setup will take. For example, a home or facility which has construction debris all over the place will take longer to setup than when it’s clean. A bigger home will require a longer setup time than a smaller home. It all depends on the complexity of the conditioned area and how long will it take to properly seal all the ducts. The objective is to create a negative pressure in the heating and cooling system and however long this will take will determine the cost of the duct leakage test.

Final Words

Besides for a newly installed HVAC system, there is still a benefit to conducting a duct leakage test to identify if the system is performing at its best. It may very well be that there are air leaks in your duct work which are causing your system to under-perform. This might be the reason as to why your home is not cooling properly on a hot summer day. If you suspect that your ducts might be leaking, call down a duct leakage specialist to perform an inspection. Yes, you can go over the duct work in your home, but chances are you will miss spots. An air duct professional will get a clear picture of the leaks and seal them properly.    

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