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  1. #1
    Join Date
    Aug 2012
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    83

    Moving Attic duct work to conditioned space to save energy. Return on Investment?

    This house is in North Carolina, about 1800 square feet. Split 3 ton HVAC system with Gas Furnance. The attic is well vented with two power blower fans, but it still feels like an oven up there. I've asked a couple of HVAC professionals about moving my coil R6 duct work out of the attic into the conditioned space and they both kind of dismissed the idea, but everything I read online says it's one of the best energy efficiency improvements you can do.

    the living room has a Cathedral ceiling so it wouldn't be that hard to drop the ceiling a little and get the main truck line into conditioned space.

    In a totally DIFFERENT home which is around 1100 sqfeet we hired insulators to apply 8" thick fiberglass insulation and covered all the coil attic ducts. The ducts are now very cool. This document states 20% improvement.
    http://www.nrel.gov/docs/fy10osti/48163.pdf

    Thoughts on why installers are telling me this is not worthwhile, yet everything I read says it is? Who's right?

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,248
    This house is in North Carolina, about 1800 square feet. Split 3 ton HVAC system with Gas Furnance.
    The attic is well vented with two power blower fans, but it still feels like an oven up there.

    I've asked a couple of HVAC professionals about moving my coil R6 duct work out of the attic into the conditioned space and they both kind of dismissed the idea,

    the living room has a Cathedral ceiling so it wouldn't be that hard to drop the ceiling a little and get the main truck line into conditioned space.

    This document states 20% improvement.
    http://www.nrel.gov/docs/fy10osti/48163.pdf
    ---------------------


    I would not refer to one who makes a living in the HVAC industry AND dismisses the energy saving aspects of 'moving duct into a conditiioned space' as a Professional.

    IT DEPENDS
    on the Installation Costs to 'move the ducts into a conditioned space'.

    First, spray foam the bottom of the 1,200 to 1,500 square foot roof deck may cost $ 3,000.

    Your A/C Annual electric cost might be $450 (probably worst case?).
    3. ton = approx. 3 kw/hr * 1,500 full operating hours for N.C.= 4,500 kW-Hr or $450 / year ( at $0.10 / kw-hr)

    At 20% [15% on page 11 of linked article] savings .. .:. operating cost savings might be in the range of $90.
    $3,000 * 2% = $60. interest. So, net savings = $30/ year.
    So one could speculate that the R.O.I is about 100 years.

    http://www.icynene.com/homeowner
    Savings could be well above 20% due to reducing leakage.

    In contrast, using your situtation of
    Providing an additional 8" of blown in insulation might be in the ball park of $400. for 900 square feet.
    Net savings are $90 - $ 8 = $82. .:. R.O.I. = 5 years.

    ... K.I.S.S. Example ...
    K eep i t S imple & S incere

    It all depends on installation cost and what one wishes to do based on their 'gut feeling'.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #3
    Join Date
    Aug 2012
    Posts
    83
    Thanks for verifying what I thought. Instead of adding insulation, I think I'm going to get some drywall/framing guys to simply remove the duct work from attic and place it behind new framing and drywall. I don't like the industrial look of exposed ducting.

    Unfortunately this is only easily done on one side of the house. For the other side I'll get the exsisting coil duct wrapped with some more fiberglass batts. It makes the ducts super big and bulky, but hopefully will save a lot of energy. R8 to R25

    The HVAC system is 17 years old, when it is time to replace it, I might consider more improvements.

  4. #4
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,139
    is the house laid out so that you can run ducts to all rooms?

    to me, this is the most important question.

    my ducts are all in fur downs inside the 76 degree conditioned space.
    compared to putting the R-8 ducts into a 100+ degree attic..its
    a no brainer. but then my house's layout is fairly simple and ducts
    were easy to run to all rooms. also my ahu & supply plenum is in
    conditioned space also.

    in the past, I've worked with hvac companies to put ducts in furdowns
    in conditioned spaces. most do not grasp the concept and you wind up
    pushing their reluctant techs to do the job. at best hvac co running
    ducts is done. then carpenter to build furdowns.

    while my savings will be a little less than table 3 of the article you linked
    this reduced savings is due to lower electric costs.
    my software shows that putting ducts inside conditioned space is the
    most savings..vs higher seer, eer, hspf or in your case afue.
    as this install has a long life compared to life of unit, the cost to do this
    install is spread over a longer length of time.

    while using foam to create an unvented attic puts ducts into semi conditioned
    space, it is once again a bandaid used to cover other issues.
    and know that unvented foam sealed attics are semi conditioned.

    things like duct leakage, house to attic leakage, and thermal bypasses
    are made less of an issue when insulation/air/thermal barrier is moved
    to the roofline, if these things were done properly to start with, by the
    tradespeople, then foam wouldn't be the cure all it is sold to be.

    then you have to factor in the problems with foam.
    unvented attics that are not air tight, complicated rooflines and uneducated
    installers, problems with chemical mixes & roof temps, roof leaks etc etc.
    and the most common problem..'average' insulation depths. dips and bellys
    between roof rafters, missed spots...and the story that 3" acts as R-30.
    the R-value per inch of foam install has to meet code. meet code, not 'act as'.

    in testing these 'unvented' attics over the past decade..most are not
    what they are sold to be.

    if you can't relocate ductwork, the easy out is to foam seal the attic.
    most cases it is much better than vented attic with ducts in attic.
    but be aware that foam companies are there to sell product. if no one
    is testing or inspecting their work, someone with no dog in the fight,
    you get what you get. not always what you were told you were getting,
    or what you paid for.

    this is why in my personal home, I first air sealed the attic floor, then
    came inside the house and completed the air barrier. insulated attic
    to R-30. put mechanicals and ductwork inside the living space.
    I'm thrilled to have cut my utility bill by more than half.

    when you insulate without air sealing, the performance of the
    insulation is reduced by air moving through the insulation.
    so rather than just blow and go..air seal first. or save your money.

    I'm curious as to how you added 8" of insulation to ducts in previous house.
    without having two vapor barriers on the ducts...how did you achieve this?

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

  5. #5
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,158
    I don't doubt a 25% savings, especially if you are moving the furnace into conditioned space. IMHO is should be code that the the equipment and ductwork be in conditioned space (this can also be done by foaming the attic). Would you be OK with one piece of exposed ductwork in the cathedral ceiling? this could save considerably on installation costs...

    Most ductwork that is in conditioned space has the registers in the interior walls blowing towards the exterior walls. When buying registers get the commercial style that have the completely adjustable face. You might even be able to get away with less total registers.

  6. #6
    Join Date
    May 2004
    Location
    south louisiana
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    3,139
    cathedral would be furred down for duct. no visible ductwork.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  7. #7
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,300
    New houses should have all duct work in furred down enclosures, IMO. But so often how new homes are designed (really...someone actually designs those things vs. mere "cut and paste" out of a stock plan computer data base?) make it difficult to run duct regardless of whether it's in an attic, basement/crawl space, or even in conditioned space chases (aka furdowns). Fundamentally I believe house design needs to change significantly to return more comfortable, energy efficient structures, but current market trends still favor the McMansion layout, which has shown in my mind to be a world of problems due to the emphasis on appearance vs. functionality.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  8. #8
    Join Date
    Aug 2012
    Posts
    83
    I'm curious as to how you added 8" of insulation to ducts in previous house.
    without having two vapor barriers on the ducts...how did you achieve this?


    Basically the existing flex duct was sprayed with foam insulation and then reglular 6" thick batts of insulation were laid ontop of the flex duct.
    Similar to this article below.
    http://www.carb-swa.com/articles/gui...03_17_2009.pdf

    Except my duct work is not Burried, it just sits on top of exsisting r30 insulation with a "blanket" over the top.

    I check on condesation every few months, but have not notice anything bad so far. There's not much air movement so that probably helps.

  9. #9
    Join Date
    Aug 2012
    Posts
    83
    "is the house laid out so that you can run ducts to all rooms?"

    Yes the AirHandler/Furnace is a horizontal Trane above the garage space (which is not furnished). It currently has a spider web of flex duct going to every single room.

    I'd love to just rip it all out and start over with a vertical unit in the garage, but that is not going to be economical to do. While I can move a lot of the duct work INSIDE the conditioned home, the AH/Furnance and main feed and return lines will be stuck in the attic for now.

  10. #10
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,139
    where are you located?
    we can't bury ducts or even have ducts in contact with each other, because of humidity here in La.
    even ducts lying on top of insulation on attic floor will condensate.


    so your plan is to move some of the ductwork into conditioned space.
    supply plenum (trunk line/plenum) will remain in attic.

    with part of the ductwork in the attic and the main feed (trunk/plenum??) staying
    in the attic..your will achieve some savings..how much?
    depends. how much is moved inside, how much remains.
    what effect does 100+ degree air have on plenum/trunk.

    what I ment by how the house was laid out so that ducts could be run to
    all rooms was this.
    is the house configured so that you can serve all rooms by furring down a hallway?
    these layouts are usually fairly simple
    living kitchen den whatever as one end of the house and hallway to bedrooms
    baths etc.

    what you need is an area that can be retrofitted
    (furred down)
    so that ducts can run thru this centrally located
    area to serve each room of the house.

    in my house the living/office & br1 are at the front of the house
    with kitchen bath & br2 at rear. furred down kitchen to serve br1
    & office. ahu in linen closet with r/a in living room furred down
    top of br2 closet to serve br2 & living room.

    only in certain layouts can houses easily be retrofitted in this manner.
    in homes where this can't be done..the other option is foam insulating
    the roofline.

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

  11. #11
    Join Date
    Aug 2012
    Posts
    83

    videos and photos

    https://www.youtube.com/watch?v=h3vgtxPtvcc

    This video shows the main duct work. The other half of the duct work is not shown in the video, because it is on the other side of the cathedral ceiling. Ideally I'd like to get rid of that spider web of supply lines in the attic to only have two very big supply lines. One feeding the length of the cathedral ceiling and the other supply line feeding the length of the hallway beneath it. Making a new header, duct work, etc, will likely cost a couple of thousand. Annual AC cost is estimated at $600, plus heat gains, I might save $150 a year. Kind of a long payoff. But it just annoys me how poorly designed this house's HVAC was built.

    http://www.allentate.com/~p2177209p~...st-Subdivision
    has pictures of the inside.

    That big supply duct you see in the video going into darkness sits right on top of that cathedral ceiling ridge. Pulling it out and putting it inside by lowering the ridge ceiling is easy.
    Ignore all my talking about zoning the system in the video, that is no longer under consideration.

    It's in North Carolina and it is humid, but not as bad as LA.
    Attached Images Attached Images  
    Last edited by newstudent; 08-26-2012 at 10:15 PM.

  12. #12
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,453
    I really don't think you would save much by moving the duct inside. If you moved all of it and the furnace/coil yes but not just some of the lines. The duct system could be designed much better and wrapped with r8 insulation but the biggest savings will be air sealing the ductwork. Then foaming the roof deck or air sealing the attic floor and better insulating the attic floor and ductwork and adding a radiant barrier to roof deck.

  13. #13
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by Shophound View Post
    New houses should have all duct work in furred down enclosures, IMO. But so often how new homes are designed (really...someone actually designs those things vs. mere "cut and paste" out of a stock plan computer data base?) make it difficult to run duct regardless of whether it's in an attic, basement/crawl space, or even in conditioned space chases (aka furdowns). Fundamentally I believe house design needs to change significantly to return more comfortable, energy efficient structures, but current market trends still favor the McMansion layout, which has shown in my mind to be a world of problems due to the emphasis on appearance vs. functionality.
    You're missing something there. McMansions focus is on the layout, features, function and they they pretty up the outside with at least 1 or as many as 3 or 4 fake architectural themes (colonial, victorian greek rivial, georgian, dutch colonial, etc.) by mising and matching fake add-on shutters, dormers, and siding types. The exterior appearance is clearly...to me at least... an afterthought.

    I do agree that with all the bazillion codes out there (some of which I think seem quesitonable and make you wonder who is really driving the requirements) it's a glaring oversight that ductwork is left in an unconditioned space on new construction. We could go one step further and set a maximum HVAC equipment size for each zone based on building linear wall size. So you might pick something like 80 linear ft/ton as a ratio. So a 2000sqft home would be limited to 2.5 ton maximum. SO rather than focus on R-values, a contractor needs to add shading, insulation, and building envelope tightness to meet that minimum requirement.

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