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  1. #1
    Join Date
    Aug 2011
    Location
    Kansas City
    Posts
    78

    Return Ductwork in Attic...or worth it?

    So after my HVAC tech did my zoning system install, which I love, we started speaking about my soon to be new variable speed 2stage goodman/amana furnace and possible addition of return ducts. Right now he said my returns are "marginal" but placement is bad, 1 10x20 return in the upstairs hall, 1 10x20 return in the downstairs living room, and 1 8x8 return in the basement. The basement return is at head height and the upstairs/downstairs returns are at the floor. Anyways there is a deep closet in the living room and he said extending the basement return up the back of the closet into the attic and adding small 8" flex returns to each room would make "any" system better, he also said to eliminate the basement return or zone it so that it only opens when the basement zone calls (not yet added). He said the basement adds to much humidity in homes, even though this one is dry he said basements are just humidity prone.

    Questions
    1. Is it worth, $$ wise, putting small returns in each room? The upstairs is just over 500sqft, downstairs <500sqft, Kansas City area, 2.5ton AC, 90k 80% furnace (going to 95% 72k), energy audit shows the three upstairs bedrooms are high pressure (I'm guessing due to no returns with doors closed)

    2. Would you do it?

    3. If I do it, do the return ducts in the attic need to be insulated?

    4. If I do it, the returns will be ceiling mounted...does this affect your decision?

  2. #2
    Join Date
    Sep 2009
    Location
    Arnold mo
    Posts
    3,967
    They have through the wall vents that act as returns. They allow the air from the rooms to return to the returns when the door is closed. I would not recommend putting any ductwork in the attic and cutting holes in your ceiling under the attic. The kind of through the wall vents I'm speaking about have built in sound & light dampers, so that privacy in the bedrooms is not comprimised.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

  3. #3
    Join Date
    Apr 2010
    Location
    NC Sandhills
    Posts
    409
    Is the 10x20 the actual filter grille dimensions or return ducting dimensions to grille. Most likely it is flex going to a 10x20 grilles which would be undersized for that system. So either go with multiple room returns or bigger central returns. Need insulation on returns in attic for sure. Ceiling mounted returns are fine.

  4. #4
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,542
    I tend to agree with Tips. I'd much rather use "thru the wall" returns than going into the attic and yes, any ductwork in attic would have to be insulated.

  5. #5
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,347
    What Tips mentioned I believe are called "transfer grills". They allow air to move between rooms but inhibit light and sound transmission.

    These grills can go above a door to a room where the door is frequently closed (such as a bedroom). Or if that is not possible, they can also go in a wall, as long as the opposite side is open to the common existing return air inlets.

    Keep any kind of HVAC duct out of an attic if you can help it.
    • 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.

  6. #6
    Join Date
    Aug 2011
    Location
    Kansas City
    Posts
    78
    Thanks, guess I'll pass on the in attic duct. All the ductwork is sheet metal, so a 10x20 grille has a 10x20 metal duct behind it.

    I'll look into "transfer grilles"

  7. #7
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,732
    Great you abandoned the attic ductwork idea!

    Is there a problem here? (Sounds like you are very happy.)

    Let's review; the purpose of this work is avoidance of anticipated humidity problem? You have 2.5 ton ac on 1000 sf house? Cause of this anticipated problem is "basements are humidity prone"? Cure is major return modifications?

    There has or hasn't been a humidity problem so far?

    If there hasn't been, blaming the basement for a new or anticipated new one seems intentional or unintentional misdirect. Maybe I missed something?

    For others reading this, ducts in attic usually lead to energy bill problems and should be avoided. There is a litany of other problems such systems create, so if this recommendation is made without discussion of all the downside, or other possible approaches, your antenna should go up. It may not be intentional self dealing at your expense, this person may simply not be qualified to give advice that puts your best interest first.

    There are often much better, more affordable solutions that just require a little creativity and collaborative discussion to come up with.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  8. #8
    Join Date
    Aug 2011
    Location
    Kansas City
    Posts
    78
    There is no problem but I want a "energy efficient" system and if new duct was required then so be it. However based on the advice given I will not be doing new duct, especially not in the attic...I'm considering transfer grills.

    Humidity...there currently is none that I can feel and the basement has never been a problem but was just warned that it could happen.

    Energy efficiency if running your AC/Heat Pump requires 14.1amps and 25amps at it's highest efficiency doesn't it still require 39.1amps, thereby costing money?

    Conservation REGARDLESS OF SYSTEM EER and SEER not running a system is the BEST savings available.

  9. #9
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,732
    When heating or cooling is optional, not running it is how you save. For most of the energy most people consume for heating and cooling, it is not optional. When it is 20f you must heat your house.

    If you think about the energy cost being continuous loss, instead of optional replacement, your orientation shifts. There is a seasonal load associated with keeping your home between 65 and 75f. Think of driving from ny to california, doing that with the car turned off does not happen. So how do you make the miles most efficiently. Foot flat to the floor using your key to control speed, or gently using the gas pedal.

    "I want an energy efficient system" ... Sounds like you'd like more than just a more efficient hvac system. Can you elaborate on what it is you'd really like? Sounds like an energy audit outlining your opportunities might be in order.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  10. #10
    Join Date
    Aug 2011
    Location
    Kansas City
    Posts
    78
    I've already had an energy audit done, which let to increased attic insulation, increase attic ventilation, increased wall insulation, adding floor insulation above garage, air sealing, double pane low e argon filled windows, all lighting changed to LED and CFL bulbs, and a new gas water heater (couldn't justify cost on tankless).

    My biggest issue with energy efficiency is that my 20 yr old furnace requires 8.1 amps minimum to operate but the new variable speed 2 stage one requires 14.1amps minimum. How are these systems getting more efficient if they require more power to operate, Yes the gas aspect is 15% more efficient but it's electricity consumption goes up...robbing peter to pay paul.

    The same can be said for my Condenser, a 20yr Nordyne 2.5ton 8 Seer unit requires 12.1 to operate and the new 16Seer two stage 2 ton system requires 15.1. Again regardless the improved comfort energy consumption goes up and the new unit will run LONGER.

    I guess I just want the best of both worlds, lower energy consumption and perfect comfort....Impossible I guess, however I'm trying to achieve a system that barely works to achieve optimal comfort.

  11. #11
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,732
    Just because your tires are rated for 120 mph doesn't mean that they EVER see that operation.

    Mark your calendar one year out (include link to this thread). Watch your bills. Compare annual over annual. I bet you save 25%.

    Awesome that you did all that. Please share results.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  12. #12
    Join Date
    Aug 2011
    Location
    Kansas City
    Posts
    78
    TedKidd - once the new furnace is installed I will take you up on that offer!

  13. #13
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,732
    Awesome, thanks!

    Can you provide the following:

    Blower door cfm50 before work: After work:


    Last years total therm consumption: Total kwh consumption:


    Year before total therm consumption: Total kwh consumption:


    Modeled savings projected, therms: Kwh:


    You'll like having it documented, this stuff tends to get difficult to dig up as time passes.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

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