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  1. #1
    Join Date
    Feb 2011
    Posts
    19

    Using 3 ton unit to cool 600 sq ft room - Is it possible?

    Before you think I'm crazy, listen to my scenario. I have a 1200 sq ft downstairs and there is a 600 sq ft addition above the carport (only upstairs area). I have one 3 ton unit for the entire house and upstairs is 20+ degrees hotter in the summer. I have to replace my downstairs unit because I don't have a heat pump and I'm heating my house on heating strips resulting in $500+ power bills in the winter. Someone suggested possibly taking the unit I am replacing and having it moved to cool the upstairs during the summer since it still works fine. I know it is important to properly size the unit for the area it is cooling because of moisture issues. He mentioned that it would probably work if you were to only use it during the summer and not drop it too low - no lower than 75, 76. He also mentioned a humidistat.

    After having 5 technicians out, the concensus is that the ideal solution is to add a separate unit upstairs. I can't afford to replace my downstairs and install a new unit upstairs but I could probably afford this solution if it would work. Thoughts? Or is this a terrible idea?

    I live in Savannah, Ga by the way.

  2. #2
    Its an awful idea.

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,320
    You will have humidity control problems with that much tonnage for 600 square feet.

    Reduce the heat gain to the upstairs portions of the house is the best long term approach to your problem. Radiant barrier, added attic insulation, airtight seal at the ceiling plane (I think ceilings should be respelled as "sealings")...you may want to consider an energy audit by a competent outfit so you can derive a long term blueprint for turning your comfort and energy problems around.
    • 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.

  4. #4
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,842
    Multi stage new heat pump and zone control for the system the way it is now?
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  5. #5
    Join Date
    Feb 2011
    Posts
    19
    So I guess this isn't an option. I've brought up zoning to everyone that has come out and pretty much all of them have said you could but it wouldn't be practical in this situation and have pretty much shot it down.

    My main issue is not enough air flow to the upstairs. I have well insulated attic. The suggestions (without adding separate unit) have been duct fan, modifying supply duct that runs to addition to start bigger (currently a 10 all the way), and upgrading main unit to 3.5 ton with some combination of the previous suggestions. There is probably 60 ft or more of duct from the unit to the upstairs supply vents along with sharp turns. I do have a return upstairs but that may need to be modified as well.

  6. #6
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,320
    To experience 20 degrees hotter upstairs than downstairs means you have some serious heat gain occurring in your house via some means. This is why I suggested an energy audit...your building shell isn't adequately protecting you from extremes in weather. When it does, your needs for heating and cooling go way down, almost to the point where ventilation and humidity control are more important than maintaining a comfortable room temperature (key word: almost).

    If the upstairs 600 square feet is fairly open, you might consider a mini-split a/c up there instead of trying to tap into your downstairs system (which is never an adequate solution - upstairs and downstairs in a multi-story house are two separate climates).
    • 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.

  7. #7
    Join Date
    Feb 2011
    Posts
    19
    Quote Originally Posted by shophound View Post
    To experience 20 degrees hotter upstairs than downstairs means you have some serious heat gain occurring in your house via some means. This is why I suggested an energy audit...your building shell isn't adequately protecting you from extremes in weather. When it does, your needs for heating and cooling go way down, almost to the point where ventilation and humidity control are more important than maintaining a comfortable room temperature (key word: almost).

    If the upstairs 600 square feet is fairly open, you might consider a mini-split a/c up there instead of trying to tap into your downstairs system (which is never an adequate solution - upstairs and downstairs in a multi-story house are two separate climates).
    Yes, I know it is not ideal to tap into downstairs but to buy a separate unit for one room upstairs just is not settling well with me. I also don't plan to live in this house for more than a couple years and do not think I'd get back what I'd put into adding a separate unit. I have brought up the minisplit and they all have said its possible but don't see a a great place to mount it. The upstairs bedroom has 6 windows - basically covering all of the exterior wall space.

    How do I go about setting up an energy audit and what would I do with the results?
    Thanks.

  8. #8
    Join Date
    Sep 2006
    Location
    Montana
    Posts
    983
    I would consider a ductless mini split heat pump, as was stated earlier. They do make cassette units that mount in the ceiling, instead of on the wall. I know LG makes one, I'm sure there are others that do as well. I know you don't want to add a seperate unit because you don't see yourself staying in the home too long. If you have the money to invest in a mini split, you'll accomplish two things. You'll be able to enjoy the space with comfort and it will make a great selling point to a potential buyer when you do sell.

  9. #9
    Join Date
    Mar 2011
    Location
    Jamestown,SC
    Posts
    45
    Replace the downstairs, and get a window unit for upstairs. Window units are cheap and if it seems to do the job, upgrade when possible to a mini split. First, get the energy audit. Check with your electric company, some will do this for free.

  10. #10
    Join Date
    Jul 2007
    Location
    Delaware
    Posts
    3,824
    Close the windows, install a reflective shield in attic and insulation. It's not the equipment size.
    Always here

  11. #11
    Join Date
    Feb 2011
    Posts
    19
    Quote Originally Posted by energy star View Post
    Close the windows, install a reflective shield in attic and insulation. It's not the equipment size.
    There is hardly any air whatsoever coming out of the upstairs supply vents when the AC is on.

  12. #12
    Join Date
    Jan 2011
    Location
    Scranton, PA
    Posts
    32
    Just get a heat pump you live in the perfect area for it.

  13. #13
    Join Date
    Feb 2011
    Posts
    19
    Quote Originally Posted by Rheem29 View Post
    Just get a heat pump you live in the perfect area for it.
    I've already decided to do that. What about cooling the upstairs? Any suggestions on that?

    Thanks for the advice - having GA Power come out to do a free energy audit.

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