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  1. #1
    Join Date
    Aug 2011
    Location
    Kingston, Ontario
    Posts
    207

    How to check for duct air leakage

    We are going to have our existing ducts sealed by contractor at same time as he installs new heat pump system. Ducts are in attic. Single return grille and 10 supply registers are in ceiling and walls.

    If I had a way of measuring face velocity at each register and at return grille, would that give me an idea of how much leakage I have on existing system?

    This would be a one time check, so I would need to use something like a low cost anemometer. Would that be accurate enough? Any suggestions for type?

  2. #2
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
    Posts
    1,644
    I don't think an anemometer would be accurate enough to detect a relatively small amount of leakage. Especially combining that error over all 10 registers. A flow hood would really be the most accurate way to measure the difference between return and supply. Not all that cheap though. This is something the contractor should have available.

  3. #3
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,046
    Your contractor should do a before and after for you. You are paying them to seal the ducts then they should be able to show you what you paid for.

  4. #4
    Join Date
    Feb 2010
    Location
    Cal
    Posts
    1,581
    Anemometer? No, useless. The testing equipment will cost you a couple G's.

  5. #5
    Join Date
    Aug 2011
    Location
    Kingston, Ontario
    Posts
    207
    Quote Originally Posted by second opinion View Post
    Your contractor should do a before and after for you. You are paying them to seal the ducts then they should be able to show you what you paid for.
    They should, but duct sealing is just an add on to heat pump installation, so sealing is not their main focus - just going to assign a helper to work on them while they are here.

    Maybe after the new system is in and before we complete attic insulation (which will cover ducts), I will have leakage checked. I have to have a second house audit done (to qualify for rebates) so maybe we can learn something from that? Maybe do blower door test with and without openings covered?

    Perhaps I could buy a hand held anemometer, just to check relative flows from registers? Might help in balancing?

  6. #6
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
    Posts
    1,644
    well, you can usually rent flow hoods (80+/day, probably).

  7. #7
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    2,998
    or when you schedule the blower door test
    schedule a duct blaster test.
    have hvac company there to see what they
    missed in sealing ducts & re-seal.
    mark actual leakage sites instead of just
    getting equiv leakage area

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  8. #8
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,168

    Great answer from Energy Rater

    or when you schedule the blower door test
    schedule a duct blaster test.
    have hvac company there to see what they
    missed in sealing ducts & re-seal.
    mark actual leakage sites instead of just
    getting equiv leakage area
    And hope they also understand airflow duct sizing and design
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  9. #9
    Join Date
    May 2008
    Location
    Picayune Ms.
    Posts
    23

    Duct sealing and new unit

    This is a costly investment to your home that should last for years. Verify you have picked the RIGHT contractor and/or get other quotes.

  10. #10
    Join Date
    Aug 2011
    Location
    Kingston, Ontario
    Posts
    207
    Quote Originally Posted by cec39466 View Post
    This is a costly investment to your home that should last for years. Verify you have picked the RIGHT contractor and/or get other quotes.
    I did get several quotes and chose the company which I felt most confident with. They were also recommended by other companies who couldn't do the Mitsubishi install for me. They are a commercial company very well thought of in our area - not a fly by nighter

    Other than confirm the duct sizing is OK for the new unit, the existing ducts are not their main responsibility. They are just supplying a helper to seal as best they can where existing ducts are accessible. New ducts will be properly sealed.

    All I wanted to do myself was see if there was a simple method to get a measure of how much of an improvement the duct sealing will make - a before & after.

  11. #11
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    2,998
    make sure that the helper is on the right page.

    mastic seals only..not duct tape or caulks
    (hvac caulk is ok..don't like it personally but...)

    mastics are paint on..in a bucket applied with a brush
    and mastic tapes..sticky gray backing, not foil only tape

    pleunm to equipment joints
    duct take offs to plenum
    duct to supply box
    and lastly mastic sheetrock (ceiling) to supply box.

    this often requies flex duct being taken off collars
    to seal completely and 3/4 around collar to plenum.
    inner liner mastic sealed,
    insulation and outer liner in full contact with plenum/supply box
    and mastic sealed.

    its a bit more that as best as they can where accessable.
    it is worth making access.

    new construction duct leakage nation wide averages 25%
    existing homes higher. its a big deal.

    best of luck
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  12. #12
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
    Posts
    1,644
    Keeping in mind, of course, that duct leakage in UNCONDITIONED space is the bad part. duct leakage into walls that are only venting into the conditioned space is not of much concern, as well as in-between floor spaces.

  13. #13
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,411
    The ONLY way to tell duct leakage is the duct blast tester. There is nothing you can do yourself except write a check to somebody who does this. Usually it costs a couple of hundred dollars to have it done. Kinda scary a commercial company is doing the install. Sounds like business is slow and they're looking for other revenue sources. Could be good or really bad for you.
    I like DIY'ers. They pay better to fix.

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