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  1. #1

    Talking Fix For Oversized Units?

    Hi all,

    I am a newbie who has helped installers troubleshoot electrical problems for over 30 years. I have read the rules and hope I am compliant!

    About 8 years a contractor installed a 3 ton 2 stage Armstrong furnace and matching ac unit, replacing a 2 1/2 unit from Janitrol. He apparently did not figure the new windows and added blown in attic insulation into the load calculations, and yep, I have cold clammy air, because the ac does not run long enough.

    I have a 3" pvc pipe bringing in outside air for combustion. May I cap that (only in the summer) to lower my indoor humidity a little?

    As I am a tech, I can wire the two speed fan motor to stay on low, but should I do this? Will it increase line pressures excessively?

    I am very vigilant about routine procedures like cleaning the condensing coil and keeping clean filters installed. Because of numerous layoffs, installing a 2 1/2 condensing unit (if it would work) is no longer in the budget. I would appreciate some input and I assure you I do not sue people; I can't afford a lawyer anyway!

  2. #2
    Join Date
    Jun 2006
    Location
    Omaha, Nebraska
    Posts
    861
    Easy fix: Install any digital thermostat which allows you to set the cycles per hour.

    I have a 5 Ton system serving 1200 square feet in my condo. Yes, it's oversized. Right now the rH is 50% because the cycles run about 10 minutes. The CPH (Cycles Per Hour) is set to 1. It does cycle more than once per hour; CPH = 1 is apparently just an arbitrary calculation used in the algorithm. I use a Honeywell Pro4000 (THD4110D1007) Tstat, but many others have this feature.

    I'm guessing your furnace is 2-stage, not a 2-stage A/C. I don't think Armstrong made a 2-stage A/C 8 years ago, but I could be wrong.

  3. #3

    Red face Thanks-sound like an idea!

    Funny how I completely missed the idea of using a thermostat. BUT, won't it just make the house colder before cycling off? I am married, and you know that THAT means, don't you?

  4. #4
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    This DIY advise here is not going to be allowed to go much further

    Should you have the qualifications, you can apply for Pro after 15 posts and get additional information in the Pro sections of the site

  5. #5

    Red face

    Quote Originally Posted by Chris_Worthington View Post
    This DIY advise here is not going to be allowed to go much further

    Should you have the qualifications, you can apply for Pro after 15 posts and get additional information in the Pro sections of the site
    busted.......and still sweaty

  6. #6
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Quote Originally Posted by boogeyman36 View Post
    busted.......and still sweaty
    Being that your in the trade, why consider contacting one of your co-workers?

    The rules in the open sections of the site are what they are, sorry.

  7. #7
    Join Date
    Jun 2006
    Location
    Omaha, Nebraska
    Posts
    861
    Let me rephrase that: call a contractor to install said thermostat.

  8. #8
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,562
    Who really knows about your situation. We aren't there. But are you sure you don't have other issues at play here. Such as leaky ductwork and leaky house. Just because you had new shiny windows and insulation put in. Doesn't really mean anything if your house isn't sealed up. While an oversized system will create excessive humidity. Make sure you exhaust all other possibilities as well.
    I like DIY'ers. They pay better to fix.

  9. #9
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,455
    Quote Originally Posted by boogeyman36 View Post
    Hi all,

    I am a newbie who has helped installers troubleshoot electrical problems for over 30 years. I have read the rules and hope I am compliant!

    About 8 years a contractor installed a 3 ton 2 stage Armstrong furnace and matching ac unit, replacing a 2 1/2 unit from Janitrol. He apparently did not figure the new windows and added blown in attic insulation into the load calculations, and yep, I have cold clammy air, because the ac does not run long enough.

    I have a 3" pvc pipe bringing in outside air for combustion. May I cap that (only in the summer) to lower my indoor humidity a little?

    As I am a tech, I can wire the two speed fan motor to stay on low, but should I do this? Will it increase line pressures excessively?

    I am very vigilant about routine procedures like cleaning the condensing coil and keeping clean filters installed. Because of numerous layoffs, installing a 2 1/2 condensing unit (if it would work) is no longer in the budget. I would appreciate some input and I assure you I do not sue people; I can't afford a lawyer anyway!
    Get to a coil temp that is 25^F colder than you return air temp. Colder ok but must not freeze-up and your supply ducts should not sweat. Lengthen the cooling cycle to as long as possible. Dry coil take approx. 30 mins. to get some water down the drain. Blower in the "Auto" mode best to avoid re-evaporating moisture back to space. But moisture will evaporate back to the home in hour without fan "on".
    At high cooling loads even an over-sized a/c should remove enough moisture to maintain <50%RH. Avoiding excess fresh is good. Not having an air change in 5-6 hours is not healthy. This is the minimum recommended by all indoor air quality experts. A CO2 meter will indicate inadequate or excess fresh air levels. Two occupants in the a 2,500 sqft home should be about 700-750 ppm CO2.
    A/c are not able to maintain <50%RH during low/no cooling load conditions. Supplemental dehumidification is need for low cooling loads with outdoor dew points of +60^F dew points.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  10. #10
    Join Date
    Jun 2011
    Location
    Wake Forest, NC
    Posts
    352
    Unless you have some real $$ to spend on installing a properly sized unit after a new load calc is done then I would buy a small dehumidifier or two and roll with it bro.

  11. #11

    Dump IT

    I would dump ? tons into the attic so the unit has longer run time. quick fix:}

  12. #12
    Join Date
    Jun 2006
    Location
    Omaha, Nebraska
    Posts
    861
    I seriously doubt that the unit being oversized has anything to do with your feeling clammy. My first home was 950 square feet above ground, cooled by a 3 Ton 10 SEER York system (not my doing). The humidity was usually 40% or less due to the undersized ductwork and thus cold coil temp. Check for leaks in the house.

  13. #13
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Thumbs down NOT Even a pun

    Quote Originally Posted by liggett66 View Post
    I would dump ? tons into the attic so the unit has longer run time. quick fix:}
    stUpity BEYOND Bounds ! !! !!! !!!!

    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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