Duct Tightness and Blower Door Tests - Tips & Resources for Success
Passing a duct tightness test
- Follow Building America duct guides:
Building America Duct Sealing Guide Overview
Sealing the HVAC Cabinet
Metal Duct Sealing Guide
Flex Duct Sealing Guide
- Test at rough-in with the blower/furnace installed.
- There are three advantages to this: First, ducts usually test tighter because duct boots are sealed directly during testing rather than at the grills. Duct boots should be sealed to the drywall and grills caulked. This rarely happens in practice, however, and results in leakage rates that are very high.. it's not necessarily the duct work, it's the boot/wall connection! Second, leaks can be found and fixed more easily. Lastly, with the furnace installed at the rough-in test, the leakage standard is the same as the post-construction standard.
- Alternatively, keep the duct work entirely in the conditioned envelope and avoid needing to test as all! Insulate and condition the basement (doesn't need to be finished) and avoid duct work in the attic (unless encapsulated). This might require creative duct work layouts for getting to the second floor or an additional duct chase.
Passing the Blower Door Test
To Build Tight:
Air barriers need to be treated like any other building detail. Put it on the plan!
- Follow the Department of Energy's Air Leakage Guide and/or Building Science Corporation's paper on Air Barriers
- Know where your air barrier is and define the air barrier location on the building plans. Make sure contractors know what/where the air barrier is. It doesn't do any good to pay for Zip System walls and then have your electrician, plumber and HVAC guy all drilling holes through it without sealing afterwards.
- Spray foam is an expensive, but foolproof way to meet tightness standards. Using open cell spray foam in the walls and rim/box joists seals up a house hassle free, but you pay for not having to mind the details...
- You don't need to use Zip Walls - plywood or OSB with taped seams (use the right tape!) works just as well.
- House wrap makes for a crappy air barrier. It's a weather barrier (i.e. rain). Don't rely on it to meet your air tightness goals.
Connecticut's EnergizeCT program provides a $300 rebate for testing (and passing) the duct tightness and blower door requirements. We will submit all paperwork to EnergizeCT on the builder's behalf.
Envelope Tightness Requirements: 3 air changes per hour at 505 pascals pressure (ACH 50)
Duct Tightness Requirements: Less than or equal to 8 CFM per 100 square feet of conditioned floor area at 25 pascals
Call DJ Harris for testing and certification
Blower Door Only: $150
Duct Tightness Only: $250 for the first system + $100 for each additional system
Duct Tightness and Blower Door Combination: $350