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Even High-Performance Homes Get Crazy Ducts

Near Net Zero Energy Home Utah Heat Revovery Ventilator Hrv

I’ve posted a lot of crazy duct system photos here in this blog.  Remember “Release the Kraken!”?  How about “Two Jellyfish Mating“?  And about three years ago I found one that instantly became my new favorite duct disaster.  But those were all in fairly standard homes.  They didn’t have any special certifications or high-performance home creds.

Contrariwise, the ducts you see in the photo above are from an apartment building going for some serious certification.  That box at the bottom is a heat recovery ventilator (HRV) and the metal box in the middle is a fan coil.  Now, they did use metal ducts and they did use a larger size than they thought they needed. 

But, I’m pretty sure they didn’t factor in the pressure drops from all those fittings.  Those ducts — or duct fittings, I should say — are way too random.  If you go back and look at my series of articles on duct design, you’ll see that I wrote about the pressure drops in a duct system coming mostly from fittings.  And 95% of what you see in that photo above is fittings.

Here are the main problems I see here:

  • Lots of pressure drop from the fittings
  • The gores (joints) on those fittings aren’t sealed
  • The whole mess is in a tiny closet

Maybe this thing will actually move the right amount of air.  But I doubt it.  It looks too randomly installed.  No one ever draws something like that in a real design.  Here’s a photo of one that does look like it was designed properly and does move the right amount of air:

Note that it’s also in a much larger space, allowing easier access.

The good news about the main photo is that when this happens in houses getting certified in a program, the verifiers can catch this stuff and have it fixed if it doesn’t perform.  That’s what’s happening on this job.

Note:  I know someone will ask if I don’t say anything so if you’re wondering why some of those ducts in the top photo are open on one end, it’s that they leave them open for some of the performance testing before making the final connections.

Related Articles

The Basic Principles of Duct Design, Part 1

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The Ductopus or the Centipede – Which HVAC Duct System Is Better?


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This Post Has 12 Comments

  1. Thanks for pointing this out.
    Thanks for pointing this out. Is there any phone or PC software that can make easy, the job of calculating pressure drop from all these pieces?

    1. Mark, the easiest way would

      Mark, the easiest way would be to add up all the equivalent lengths, calculate the friction rate, and use a ductulator to size the ducts.  (But many installers use the ductulator incorrectly, assuming rather than calculating the friction rate.)  I don’t think they did anything like that on this job.  The verifier who sent me the photo said this wasn’t the way it was supposed to be installed and it’s being fixed.

  2. Just to get some perspective
    Just to get some perspective on the top photo, do you know what the design airflow rates are for the HRV and the air handler?

    1. Roy, no, I don’t know that,

      Roy, no, I don’t know that, but the verifier was pretty sure this system wasn’t going to work.  As I said in the article, it’s possible they might get enough air flow but it would probably be a happy accident.

  3. Hi Allison. Two of the 4
    Hi Allison. Two of the 4 ducts on the HRV are supposed to have insulation on them. I realize this may be an incomplete installation, but it seems highly unlikely that the insulation can be installed effectively – or verifiably.

    1. John, yes, that’s absolutely

      John, yes, that’s absolutely true.  Even here in Georgia, uninsulated intake ducts collect condensation in winter.  I’ve seen ceilings damaged when that condensation drips on them.  I should have mentioned this in the article, too, but didn’t think of it till someone mentioned it on LinkedIn and now you’re bringing it up here.

  4. I think one lesson to
    I think one lesson to homeowners and designers is, don’t skimp out on the space for mechanicals. Even fresh air. Lack of planned space tends to encourage this kind of install–it doesn’t excuse it–but I see all too easily how they’re just trying to make it fit, and the duct designer or site super’s not around that day to talk it through and, stuff ends up being squeezed in. A lot of times every possible supply and return location is not accounted for in the home design, and especially in more unforgiving situations like houses on slabs with vaulted ceilings, the homeonwer’s going to want to argue for all the space they can possibly have for their own uses… it still seems like there’s often an unanticipated need for more service space than was planned for. ERV/HRV sizes are really variable too…some are quite sizable, like the one in that picture, and some are very compact, and knowing which one you’re planning to put in makes a difference!

  5. In Florida, lots of builders
    In Florida, lots of builders still put air handlers in attics, where it is only 120 degrees or so in the summer. Makes for really easy maintenance and repairs. I see plenty of problems with them as a forensic engineer from condensation, leaks, and inevitable condenser pan leaks (and the automatic overflow shut offs fail a lot)…

  6. How do we as contractors,
    How do we as contractors, auditors, raters etc. Educate builders on things like this. Someone knew that this system was going to look something like this, and they just rolled their eyes and installed it anyway. It is going to take everyone from the architect who only allowed this much space, the salesman who sold it, the technician s that installed it, to stop and say this is not acceptable. I refuse to sell spray foam insulation for a new home unless blower door testing and a ventilation system are in the specs. Someone should stop and say “no, this is not going to work”

    1. They know but for whatever
      They know but for whatever reason the owner or the designers opt to preserve as much GLA as possible.

  7. Please bring challenge of
    Please bring challenge of ACCA Manual D methods, into this conversation. We do crazy things treating air flow as toothpaste-to-be-squeezed, without regard of velocities and energy losses, according to Bernoulli Principle. The word Bernoulli is unknown to ACCA. I despise D-boxes as criminally absurd. Air must move in guided paths at steady velocity for best control and efficiency.

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