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  1. #1
    Join Date
    Aug 2005
    Posts
    2
    Hi Everyone! I was recommended this site by a co-worker after discussing some of my recent HVAC issues…

    I’ve read through some of the recent posts, looking for answers, and while I’ve seen some that are similar, haven’t really seen a post related directly to my issue…

    Details: I live in Charlotte, NC (where the summers are HOT and the winters are cool/cold), in a fairly new (9mo old) townhome (brick exterior, minimal windows), roughly 1,200 sqf, 2 bedroom (upstairs) 2.5 bath (one in each bedroom, ˝ bath located downstairs).

    Floorplan: http://www.meetingstreethomes.com/plans.asp?SID=1&ID=4

    System Configuration: The HVAC unit is located in the attic. Upstairs is fed by two “main” ducts, one to each bedroom, controlled by a manual damper. In addition to the two main ducts, there are also smaller lines, to each of the following: master bathroom, master closet, guest bathroom, and guest closet. Downstairs is fed by one large line, and is split into three lines, one in the kitchen, one in the dining room, and the last (and furthest) in the living room. The unit is controlled by a digital thermostat, located downstairs, in a central location.

    Issue: Unlike the typical issues I’ve read here, and discussed with others, my issue is that upstairs is cool, and downstairs is warm/hot.

    Steps to Resolution: The HVAC contractor came out and adjusted the dampers to limit the airflow upstairs, resulting in more downstairs, made sense to me!

    He suggested that this might need to be adjusted throughout the year, as once it began to get warm, we would want more airflow upstairs rather than downstairs, b/c naturally heat rises, cool air falls, so downstairs would be comfortable and upstairs would be warmer. Again, made sense to me…

    Unfortunately, I have been unsuccessful with balancing the system. The dampers upstairs are about 25% open, which keeps upstairs comfortable, actually a little cool. Any less and upstairs gets too warm for my comfort level. My assumption is that the remainder of the air would be going downstairs, but this doesn’t seem to be the case. Downstairs is on average 7-10 degrees warmer than upstairs. I’ve tried closing the upstairs dampers, assuming that ALL of the air would be forced downstairs. This has resulted in a warm upstairs, and a warm downstairs.

    The HVAC contractor has come out SEVERAL more times and has suggested that the system is operating normally, which I’m not convinced of. I would like to have the inside temperature maintain at 72 degrees, upstairs and down, which would seem reasonable with properly adjusted dampers.

    I’ve been told that it is best not to install a programmable thermostat, and to set it on your desired temperature and do not touch it. This is exactly what I have done. The thermostat is set at 72 degrees, and in the morning, the house is fairly comfortable. As the day warms up, the inside temp rises, and rises (while the system continues to run). By noon downstairs is typically 74/75 and upstairs is roughly 70. By 5:00 PM, downstairs is 75/77 and upstairs maintains at 70. The system runs pretty much all day long, and into the evening. Sometime around midnight, shuts off for the night.

    The temperature from the vents downstairs is about 63 degrees, which appears to be pretty good, however the airflow is barely noticeable. While the airflow upstairs is extremely noticeable.

    This has brought me to the conclusion that there is something prohibiting the air from freely flowing downstairs.

    The HVAC contractor disagrees. They have suggested that I have a zoned system installed, controlled by electric dampers, with an additional thermostat upstairs. At first this sounded like an excellent solution, however after thinking it through, I am still not convinced that would resolve my issue.

    Question: Given my current configuration and issues – would a zoned system resolve my issue of a warm downstairs, and a cool downstairs?

    Based on my limited knowledge and understanding, I disagree that it would. I make this assumption based on my experience with closing the dampers upstairs, forcing the cool air downstairs, which did not work, and I ended up with a warm house, down/up.

    Could there be either a leak or blockage in the main trunk going downstairs and/or in the distribution box? I assume the HVAC contractor would rather not go there b/c in order to access these items, a lot of drywall would have to be removed/replaced. The system is under their full warranty for another three months, and I would like to have this issue resolved before the warranty expires.

    Sorry for the LONG post – my intention was to provide you (the experts) with as much information as possible w/o having to go back and forth. I do look forward to hearing back from you all!

    Many Thanks!
    -Greg

  2. #2
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,763
    sounds like duct to downstairs either blocked or extremely undersized. might have to open duct in attic to look down thru it. would not attempt zoning if closing upstairs dampers does not help.

  3. #3
    Join Date
    Nov 2004
    Location
    Michigan, Detroit Metro area
    Posts
    296
    Where are the returns located?

    If there is only a central return in the upstairs cieling, then the rooms on the first floor may not have enough return air for the supply's to work properly.



    What's my post count now?
    UA Local 636

  4. #4
    Join Date
    May 2005
    Posts
    44
    Call builder, and tell them get whoever and fix the problem.

    Sounds like design issues.




  5. #5
    Join Date
    Nov 2004
    Location
    Thibodaux, LA
    Posts
    1,170
    Your problem is the exact opposite of the normal. Normal would be hot upstairs in summer hot upstairs in winter.

    Do you have a door between upstairs and downstairs and a single return upstairs? If so this could be your problem.

    I never like to install one system on a two story unless its zoned. You'll never be able to balance the one system.

    "Football Season again finally"

  6. #6
    Join Date
    Aug 2005
    Posts
    2
    Hi Everyone!

    Thank you so much for the responses thus far!

    There are two returns, both in the stairwell area. The one upstairs is at the up most top of the stair well. The one downstairs is at the bottom of the stairwell, just above the platform that takes you into the kitchen/dining room area. There are no doors (or anything for that matter), between the two returns, up and down.

    The ductwork going downstairs is fairly large, at least, from what I can see in the attic going down the cavity. It is black in color, and I can assume that it has an insulated wrapper… I’d say that the entire piece is approximately 16 inches wide (maybe more). Assuming that a part of that is insulation, would that mean that the duct itself is about 12 inches? Should be sufficient to push air to the downstairs, right?

    I’ve had the builder over here a few times and he agrees w/ the HVAC contractor that the system is operating normally. Also, this is the exact configuration of a dozen or so other townhomes in the neighborhood, and no one else is as vocal about the heating/cooling of their home.

    The last time the HVAC contractor was out, he said that on the days the temp is getting into the 90s and beyond, that the system won’t cool the house more than 18-20 degrees below the outside temp… but I argued that upstairs maintains at or around 70 (sometimes less), while downstairs gets into the upper 70s.

    I’m not sure if there is a resolution to this issue, but I totally agree w/ everyone here that my issue is opposite from the norm.

    As far as the thermostat goes, any feedback on RonCo theory of “set it and forget it”? Or should I bump it up to say 75 in the morning when I go to work, and take it back to 72 when I get home? If so, would a programmable thermostat provide value in doing this task automatically?

    Thanks All!
    -Greg

  7. #7
    you cannot control the temperture of a two story home with one ac, cannot be done by manual dampers or duct sizing.
    you have two options.
    1. is to install another system which would cause higher utilities, more maintenace costs, costly installation.

    or have a 2 zone zoning system installed which would cost a lot less than installing another system, lower your utilities and keep each zone at setpoint assuming the system is properly sized for the square feet of home you have and also could help in situations where duct sizing is not acurate

  8. #8
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    Originally posted by airworx

    1. is to install another system which would cause higher utilities
    I have found that properly sized and installed, a 2 unit, 2 zone system will be more energy efficient than a single unit 2 zone. It is analagous to having a 2 stage or dual compressor unit. When both units are running, it's an energy wash, but usually one unit runs and some percentage time with both running. When only one is running it is a net savings. Also the units tend to run closer to rated capacity (if properly sized) and efficiency is highest at that operating point.

    I agree on the higher install cost and potential for higher maintenance costs.

    paul

  9. #9
    This doesn't make sense.

    Why doesn't closing the vents upstairs increase the airflow downstairs? Could there be a manual damper in the ductwork that adjusts the airflow between the floors that needs to be adjusted? Should the contractor measure the airflow coming out of the vents to confirm there isn't an obstruction?

    I'm not a HVAC contractor, only a homeowner, but this doesn't add up.

  10. #10
    you probably add dampers. more than likely the duct design
    is wrong. and manual dampers will not work unless you do an air balance test and then your wasting your money because as the seasons change so will the damper adjustments.
    a 2 zone zoning system is your best way out.
    now one other thing you can do is calculate the duct sizes
    from the mains to the branches then take that to a contractor to see if it is even close. if you have more duct capacity than blower cfm then theres your problem.
    example would be you have a 2 ton system which pushes 800 cfm, well if the ducts are oversized say you have 5 8" main duct runs well the ducts could carry 1150 cfm and would be of course oversized and low air flow would be created.

  11. #11
    Join Date
    Nov 2004
    Location
    Michigan, Detroit Metro area
    Posts
    296
    "Why doesn't closing the vents upstairs increase the airflow downstairs?"

    http://www.orionfans.com/html/static_pressure.html

    http://www.efi.org/articles/static.html

    Closeing the damper probly is causeing more air to go downstairs, but not enough to matter.


    What's my post count now?
    UA Local 636

  12. #12
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697
    If your house and ducts are tight and have low leakage, the cold air upstairs should tumble down the stairway while the hot air downstairs rises up the stairway. It should not take long for the temperatures to equalize within 3 °F or less.

    If your temperature difference is really as great as you say it is, your house and duct system must leak like a sieve. I suggest you insist your builder hire an expert to test the house and the ducts for leakage -- and fix the leaks.

    You should also insist that your builder get the HVAC contractor to tear out walls -- or whatever it takes -- and fix the inadquate duct system. The air flow out of each supply grille should be about the same as all the others of the same size.


  13. #13
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,428
    Originally posted by vwmann
    The ductwork going downstairs is fairly large, at least, from what I can see in the attic going down the cavity. It is black in color, and I can assume that it has an insulated wrapper… I’d say that the entire piece is approximately 16 inches wide (maybe more). Assuming that a part of that is insulation, would that mean that the duct itself is about 12 inches? Should be sufficient to push air to the downstairs, right?

    I’ve had the builder over here a few times and he agrees w/ the HVAC contractor that the system is operating normally. Also, this is the exact configuration of a dozen or so other townhomes in the neighborhood, and no one else is as vocal about the heating/cooling of their home.
    Did you compare downstairs air flow to other units?

    Does everyone else have their temperature set at 80'F?

    I would guess your 1,192 square foot unit with 8 small-medium sized windows is ~ 2_ton ( 800 CFM) or 2.5-ton (1,000 CFM) system for Charlotte NC.

    Hopefully, it is NOT a Rheem.

    12" duct is suffcient if not stuffed with a pillow or attic insulation and will generally provide > 500 CFM downstairs.

    The A/C contractor must measure each diffuser and return air with balometer and adjust to permit adequate air flow downstairs accordingly.

    I am sure more will follow ..
    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

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