Duct Tightness Testing (IECC 2021)
Since 2009, under the IECC Code, ducts, air handlers and filter boxes shall be sealed, and joints and seams shall comply with either the International Mechanical Code or 2021 International Residential Code. The 2021 Illinois Energy code brings testing to all duct systems regardless if 100% of all ductwork is located within conditioned space (see definition below) or not. A Duct Tightness Test must be performed to verify compliance. This means that any time you run ducts inside or outside the building envelope (in the attic, crawlspace, or garage, for example), the entire system must be tested.
Priority Energy has experienced BPI-certified Duct Test technicians who will conduct the test and provide a signed, written report for your Village Code Official.
It is not an easy test to pass.
Click here to see Duct Test results from across the Chicagoland area.
There are different standards to determine allowable leakage depending on when the ducts are tested and where they are located:
Ducts shall be pressure tested to determine air leakage by one of the following methods (IECC Section 403.3.5)
A Rough-In Duct Test
If this test is performed before the air handler or registers are installed (typically before drywall), the requirement per IECC 2021 is 3 cubic feet per minute (CFM) of leakage (at 25PA or 0.1IWC, the normal operating pressures of a duct system) per 100 sq. ft. of conditioned floor area.
If the duct test is performed after the air handler has been installed the IECC 2021 allowable leakage is 4 CFM of leakage per 100 sq.ft. of conditioned floor area.
At the rough stage of construction most well-sealed systems Pass, or if they don’t Pass it is still possible to locate the leakage points, seal them and perform a re-test.
Exception: if the duct system is serving less than 1,500 sq. ft of conditioned floor area, the allowable duct leakage shall be 60 CFM or less.
For example: If you have an HVAC system serving the second floor of a house with ductwork running in the attic, and the second floor is 1,600 sq. ft., only (1600/100 x 3) or 48 CFM of leakage will be allowed in the system. This is not a lot when you factor in all the connections in a typical duct system (take offs, elbows, boots, cleats, etc.).
A Post-Construction Duct Test
Priority Energy does not recommend waiting until completion of the home to perform a duct leak test as it becomes much more difficult to attain the minimum air leakage requirement once the air handler and register covers have been installed.
We understand that sometimes the duct test is missed and needs to be done later in the construction process or after completion. Priority Energy can help, but our technicians want you to know that it is not uncommon for most systems to Fail once a home gets further along in the construction process.
A finished home is allowed 4 CFM of leakage at 25 PA/0.1 IWC per 100 sq ft of conditioned floor area. While you may be thinking this has increased the amount of acceptable leakage (64 CFM from our previous 1,600 sq. ft. second floor example), and should be easier, it is not. Factors such as the ductwork being concealed by drywall and insulation, an installed air handler (which can leak as much as 100 – 200 CFM on its own), and registers being in place combine to make a much leakier and harder to seal internal system. To test at this stage means we have to tape over these areas and also test the connections between the boot and subfloor/drywall, which is not ideal.
Exception: if the duct system is serving less than or equal to 1,500 sq. ft of conditioned floor area, the allowable leakage shall be 60 CFM or less.
Ducts Within the Thermal Envelope
Regardless of when the system is tested: Where all ducts and air handlers are located entirely within the building thermal envelope, total leakage shall be less than or equal to 8.0 CFM per 100 Sq. ft of conditioned floor area. So if the the ducts for the 1,600 sq. ft example above were running with the conditioned space, the allowable leakage would be (1,600/100 x 8) or 128 CFM.
Exception: If the duct system is serving less than or equal to 1500 sq. ft. of conditioned floor area, the allowable duct leakage with the air handler installed shall be 60 CFM or less
If your Ductwork Fails the Duct Test
Our technicians evaluate duct systems every day and can help you locate the leakage points in your system with our diagnostic equipment. (There is an additional charge for this service.) We will provide you with as much guidance as possible, but depending on where the leaks are located and how much leakage is occurring, your best and only option may be to use Aeroseal, the aerosolized, non-destructive duct sealing process.
Priority Energy is an authorized Aeroseal provider to the Chicago area.
Ductwork in Conditioned Space*
For ducts to be considered as inside a conditioned space (IECC Section 403.3.2), such ducts shall comply with one of the following:
- The duct system shall be located completely within the continuos air barrier and within the thermal envelope.
- The ducts shall be buried within ceiling insulation in accordance with Section R403.3.3 and all of the following conditions shall exist:
The air handler is located completely within the continuous air barrier and within the building thermal envelope.
2.1. The duct leakage, as measured either by a rough-in test of the ducts or a post-construction total system leakage test to outside the building thermal envelope in accordance with Section R403.3.5, is less than or equal to 1.5 cubic feet per minute per 100 square feet of conditioned floor area served by the duct system.
2.2. The ceiling insulation R-value installed against and above the insulated duct is greater than or equal to the proposed ceiling insulation R-value, less the R-value of the insulation on the duct. - Ductwork in floor cavities located over unconditioned space shall comply with all of the following:
3.1.A continuous air barrier installed between unconditioned space and the duct
3.2. Insulation installed in accordance with section R402.2.7
3.3. A minimum R-19 insulation installed in the cavity width separating the duct from unconditioned space - Ductwork located within exterior walls of the building thermal envelope shall comply with the following:
4.1. A continuous air barrier installed between unconditioned space and the duct
4.2. Minimum R-10 insulation installed in the cavity width separating the duct from the outside sheathing
4.3. The remainder of the cavity insulation shall be fully insulated to the drywall side
