Ducts in unconditioned space
Subject: Ducts in unconditioned space!
By: Tom Bawolek, Five Star Energy Corp. 414-659-2290
We have seen a recent increase in building code officials asking for “duct leakage testing” documentation.
The purpose of this memo is to inform builders, contractors, and building code officials of what this means and how this testing is completed for compliance.
First, here’s the actual code language………….adopted Jan 2016 in most recent update to IECC 2009
SPS 322.43 Duct and plenum sealing.
(1) Duct systems with joints not located entirely within the conditioned space or with joints located on the unconditioned side of stud bays, joist cavities and similar spaces, shall be sealed in accordance with this section.
(2) Sealing shall be accomplished using welds, gaskets, mastics, mastic-plus-embedded-fabric systems or tapes installed in accordance with the manufacturer's instructions.
(3) Insulation that provides a continuous air barrier may be used in lieu of sealing metal ducts.
(4) Tapes and mastics used with rigid fibrous glass ducts shall be listed and labeled as complying with UL 181A.
(5) Tapes and mastics used with flexible air ducts shall be listed and labeled as complying with UL 181B.
(6) Tapes with rubber-based adhesives may not be used.
(7) Except where exempted as indicated in sub. (8), duct tightness shall be verified by either of the following:
(7)(a) Postconstruction test: Leakage to outdoors shall be less than or equal to 8 cfm per 100 ft2 of conditioned floor area or a total leakage less than or equal to 12 cfm per 100 ft2 of conditioned floor area when tested at a pressure differential of 0.1 inches w.g. (25 Pa) across the entire system, including the manufacturer's air handler enclosure. All register boots shall be taped or otherwise sealed during the test.
(7)(b) Rough-in test: Total leakage shall be less than or equal to 6 cfm per 100 ft2 of conditioned floor area when tested at a pressure differential of 0.1 inches w.c. (25 Pa) across the roughed in system, including the manufacturer's air handler enclosure. All register boots shall be taped or otherwise sealed during the test. If the air handler is not installed at the time of the test, total leakage shall be less than or equal to 4 cfm per 100 ft2 of conditioned floor area.
(8) A duct tightness test is not required if the air handler and all ducts are located within conditioned space.
Note: Standard duct tape or “duck tape" has a rubber-based adhesive and does not comply with the requirements of this section.
History: CR 08-043: cr. Register March 2009 No. 639, eff. 4-1-09; CR 15-041: cr. (7), (8) Register December 2015 No. 720, eff. 1-1-16; numbering correction in (7) made under s. 13.92 (4) (b) 1., Stats., and correction in (7) (intro.), (b) made under s. 35.17, Stats., Register December 720, eff. 1-1-16.
Here’s my commentary on each of the code sections above:
(1) any portion of ducts located in unconditioned space, including jump return ducts, ducts in vertical walls if they do not have R10 to outside, and ducts in floors over garage if they do not have R19 to outside.
(2)Only the ducts OUTSIDE of conditioned space need to be sealed if test option (a) is used for compliance. ALL ducts would need to be sealed to utilize test option (b). Test option (a) is best!
(3)i.e. closed cell foam encapsulating ducts is ok
Test option (a) can only be completed at final inspection because it requires the building to be pressurized to 25 Pa with a blower door simultaneously pressurizing the duct system. This interaction isolates duct leakage to OUTSIDE and eliminates duct leakage that may be occurring within conditioned space. We have been completing this testing in many homes over the years for purposes of tax credits and Focus on Energy standards. Just seal the unconditioned space ducts seams, connections, AND rough openings at top plates or wall openings to/from conditioned space and you should be good to go to meet this criteria.
Test option (b) requires all ducts and grilles/registers to be in place by rough inspection and ALL ducts sealed, whether they are in conditioned space or not. This test criteria is difficult to achieve.
Most of our builder partners have an option price already in place with us for this additional level of testing. Note that since documentation will need to be provided to the code official we will need to complete this testing prior to final so all the ducting, registers, and grilles need to be in place and completed so we can tape them off.
