Is This the Worst Duct Retrofit Ever?

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1. Wait, no UL181 tape or mastic
   Wait, no UL181 tape or mastic on that downspout?! Shame. [Sarcasm]

2. What the equivalent length
   What the equivalent length and static of that assembly?

3. Awesome!
   Awesome!

   I have a question for anyone who knows HVAC. My now-defunct Atlanta builder installed a zoned (2 zone) system in our house.

   This system has a passive bypass damper that is designed to bleed excess air when only one zone is in use and the air from the bypass damper was originally routed back into the return side of the system.

   A few years ago our compressor failed and the owner of the HVAC company said that it failed because routing the excess air from the bypass damper back into the return prevented all of the refrigerant converting into a gaseous state. Consequently it was this refrigerant returning to the compressor in a liquid state which caused premature wear and failure.

   His solution was to disconnect the bypass damper from the return and allow the excess air to vent into the vented attic space.

   Since then I’ve had two HVAC companies out over the years to perform semi-annual inspections and they’ve both questioned this set up, but they’re unable to tell me that our reasoning isn’t sound.

   Thoughts?

   1. That sounds wrong to vent the
      That sounds wrong to vent the conditioned air outside of the conditioned space of the home.
      The excess air should return to the house at some point. Not the vented attic, do not even have the excess air return to the return coil without its time in the conditioned space.
      Venting into the attic throws the house into negative pressure as well as wastes the conditioned energy that should have gone into the space.

      1. Agree, The stack effect is
         Agree, The stack effect is in full display with the out of square custom windows/doors and lack of air sealing.

         It sounds wrong, but is it sound reasoning (ie. You shouldn’t recycle cooled air back into the system)? The bypass damper is located just off the plenum and designed to channel condition air into the return via 3 ft of flex duct.

         In an ideal world I’d tear out the entire system and have it redesigned but I don’t have the space or permission. 😉

   2. Discharging to the attic is
      Discharging to the attic is ridiculous and the installer who did this should be turned over your knee and spanked.

      Every cubic foot of air now gushing into your attic is coming from your return air duct and air handler. When the exact equivalent volume of air is not ducted back into the house through the supply duct system, the difference must come into the house through gaps, cracks and bypass openings in the skin of the building.

      If the HVAC unit truly can’t work as a two-zone system then open both dampers and cap the bypass. And, do so with metal, screws and mastic…..not rain gutters, rope and garbage bags. You’re paying to condition the air so it must be directed to your house rather than outdoors via the vented attic.

      Before you do this obvious repair though, you need to send a photo to Allison for his wall of shame catalog, and don’t forget to include the names of the guys who routed the duct to the attic and the guys who left it that way without rolling on the floor laughing.

   3. One should never vent
      One should never vent conditioned air into the attic. One should also never use a bypass — see http://www.proctoreng.com/energy-efficiency/zones.html
      The fix to your problem is to close off the old bypass (now converted to a duct leak to the attic) close it off at both places (supply plenum and return plenum). Then put damper stops on the two dampers so they do not close completely. This will allow some conditioned air to flow into the zone that is not calling for conditioning at that particular time, but will eventually.
      There is also a discussion of zoning somewhere on Allison’s blog, but I don’t know how to direct you to it.

   4. Fix this ASAP.
      Fix this ASAP.
      1) this is raising the utility bill
      2) depressurizing the home and puling air from unwanted sources. such as attic, crawlspace, chimneys
      3) increase particulates in the home is possible
      4) if you are in a hot humid climate this can be causing a “M” (mold) issue
      5) if in a cold climate causing low house humidity

      This is a bad, bad, bad and very bad installation and repair. Said to say somewhat typical.

      1. Thanks for the input. I’m in
         Thanks for the input. I’m in climate zone 3A (mixed-humid), but as you can see we’re afraid of loosing another compressor and two HVAC companies who commented this set up were unable/unwilling to address our primary concern (i.e. compressor failure). We even had one technician state that he didn’t want to disturb the flex duct because it was an old (circa 1999) type that is prone to tearing.

         I have some DIY ideas in mind outside of a gallon of gasoline and a match.

   5. Contractors have been taught
      Contractors have been taught to install bypass in zoned systems. When done properly (in my experience, that’s rare), it will work, but best case, it will impair the efficiency of your system. Worst case, well, you already know what can happen. The liquid refrigerant doesn’t fully evaporate and repeatedly “slugs” the compressor, eventually killing it. California is the first state to prohibit bypass (with some caveats).

      There are several ways to maintain proper airflow across the evaporator coil in zoned systems without resorting to bypass. Hint: dumping supply air in a vented attic isn’t one of them. The trick is finding a contractor who understands how to design zoned systems.

   6. Dumping excess air into
      Dumping excess air into return is correct way to remove excess static when one zone closes. Damper may not be adjusted to correct opening position during this process , you could have variable speed furnace or air handler installed with Honeywell control board that ramps blower to correct proper airflow to each zone,this is somewhat costly but will correct flooding of refrigerant to compressor,l have 30 yrs experience and guarantee this is correct fix to your problem

4. Is this a photo shop picture?
   Is this a photo shop picture? The proportion of downspot material seems very wrong compared to the concrete lift block and the air handler.

   1. I thought the same thing at
      I thought the same thing at first but believe it is the perspective of the photo with the gutter being much closer to the camera.

5. Necessity is the mother of
   Necessity is the mother of invention!

6. @ Johnny I have to
   @ Johnny I have to respectfully disagree with you. Thirty years of experience with zoning, I presume that you have found that a “properly installed” bypass reduces noise on the zone that is calling for conditioning. The bypass is based on the concept of “excess air”. However, it is important to look at more than experience (which varies between those who still use bypasses and those who do not). It is important to look at what the scientific studies show. I suggest that you take the measured data seriously. The data show what happens when the bypass is open, the capacity drops and the efficiency drops. What this means is that the capacity and efficiency are considered “excess” by opening the bypass. This is both unnecessary and counter productive. There are ways to shift part of the capacity between zones and maintain the efficiency of the unit. I respectfully suggest that you read the information from the Carrier test contained in http://www.proctoreng.com/dnld/H114.pdf
   To quote:
   This paper states:
   “Capacity and EER drop significantly with increasing air bypass for both the air conditioner and heat pump. The capacity and the EER of the air conditioner decreased 47% and 46% respectively with an increase in bypass from 0% to 79% for DOE A test conditions.”
   Note that the reduction in capacity produces an almost equal reduction in efficiency. This is because the watt draw of the condensing unit changes very little as the indoor coil gets colder.
   Note the graph of Page 9.

   1. John:
      John:

      Great answer, let the data speak for itself.

7. +1 John Proctor. Folks aren’t
   +1 John Proctor. Folks aren’t going to easily let go of what they’ve been taught and have practiced for decades.

   1. David:
      David:

      I agree we all can get set in our ways until we can experience a better way. I would encourage “Johnny” (with due respect) to do measuring of what he is recommending to see it may not be the answer. It not only reduces efficiency it can also freeze the coil in cooling and overheat heat exchanger in heating.

      I have a philosophy to never believe anything anyone tells me without proof. Show me the data.

      1. @Andy, Johnny says he’s been
         @Andy, Johnny says he’s been at it for 30 years. Sounds like he knows how to do bypass ‘correctly’ so as to avoid the problems you mention (as I said, a properly designed bypass will work just fine). But the efficiency impacts, while real, are hard to measure in-situ.

         Here’s a great video Proctor put together using a lab setup to demonstrate the impacts: http://bit.ly/1lxxQoE.

         This bypass discussion is a bit of a side-show to the main point of this article. Here’s a previous Energy Vanguard article about bypass: http://tinyurl.com/bxg4eyt

8. Craig’s List and Chuck with a
   Craig’s List and Chuck with a truck at your service!

9. I am happy that you continue
   I am happy that you continue to write informative articles. Did you see the tour that Corbett is conducting? It was mentioned in HOME ENERGY’s newsletter.

10. Yes, Dixie, I’ve been
    Yes, Dixie, I’ve been watching the news of Corbett’s tour. We’ll see him here in Atlanta next year.

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