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Community and Q&A

Duct Blaster testing

schreibdave15 | Posted in General Questions on

We are building a new home outside of Syracuse NY. Apparently the building codes around energy efficiency have just changed however our building permit was issued under the previous code. Anyway our builder has asked his HVAC sub to do a duct blaster test on our duct system in order to determine whether the standard duct installation measures (taped seams) will be enough to meet the new code. If not they will presuambaly take additional steps for future builds, though not necessarily for mine.

My question is, once they do the test and identify the rate of leakage from my ducts and presumably where that leakage is coming from … how hard do I push them to tighten those leaks up?

Some info on my house: 3000 sqft ranch including 1000 sqft in the finished basement. 96% efficient 2 stage natural gas furnace with 2 zones – 1 basement and 1 on main floor. No ducts in exterior walls or in the attic. Rim joists will be flashed with closed cell foam so registers in those areas (several) will likely be sealed to the sub floor. If they aren’t I will likely do that myself. The main trunks in the basement will be above the finished area and therefore covered in sheetrock. The unfinised space will likely have foam board insulation on the block walls and will be used for a work out room and a work shop so having conditioned air leak into the unfinished space would not be a terrible thing.

Do I care if my ducts are more leaky than the new code will require or will less aggressive duct sealing work well enough in my situation? Thanks

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  1. GBA Editor
    Martin Holladay | | #1

    Your builder is required to meet code. I'm not sure whether your house falls under the old code (the code which presumably did not require duct leakage testing) or under the new code (which apparently does). But if the duct leakage limit applies to your house, your contractor is required to meet the code.

    Moreover, for at least twenty years, all U.S. building codes have required residential HVAC ducts to be substantially airtight. The rarely enforced provisions are found in two locations in the code. One section has long required that “Ducts, air handlers, filter boxes and building cavities used as ducts shall be sealed,” while another section has required that “Joints of duct systems shall be made substantially airtight by means of tapes, mastics, gasketing or other approved closure systems.” (For more information, see Sealing Ducts.)

    The fact that most builders have been getting away with non-compliance does not make non-compliance legal.

    All of that said, there is little evidence that duct leaks will raise your energy bills, as long as (a) all of your ducts are inside of your home's thermal envelope, and (b) you've done a good job of air sealing your rim joists. At worst, a serious duct leak might make some rooms a little too hot or too cold -- but as long as your duct system was well designed, that would be rare.

  2. Jon_R | | #2

    I would make sure that they check every closed door room for pressure balance (indoor vs outdoor) during the various combinations of zones. Imbalance will increase energy bills and wall moisture risk.

  3. schreibdave15 | | #3

    "check every closed door room for pressure balance"

    If there was an imbalance, how weould they fix it?

  4. GBA Editor
    Martin Holladay | | #4

    Here is a link to an article that describes the problem that Jon is talking about -- and also discusses ways to fix the problem: Return-Air Problems.

  5. schreibdave15 | | #5

    ok. I have returns in every room except the bathrooms. Not sure why there are no returns there. Should I care?

  6. GBA Editor
    Martin Holladay | | #6

    It's OK if your bathroom has no return air grille. That said, it's best if: (a) the bathroom door is usually left open, and (b) there is a significant undercut on the door. The door undercut also helps the exhaust fan work more smoothly when the furnace isn't operating.

  7. Expert Member
    Dana Dorsett | | #7

    The exhuast fan cfm is miniscule compared to heating air. Even without the door cut the bath fan would easily pull air from the supply ducts when the furnace isn't running unless the register was closed too.

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