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  1. #1
    Join Date
    Aug 2011
    Location
    San Diego, CA
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    Question Mini Ducts added to existing HVAC system

    System does not have enough vents to properly heat and cool home. Want to add mini-ducts to existing duct work-without adding the high velocity air handler. Two story town-home about 1300 square feet. New heating system was installed in 2007. Purchased home in 2008 and added air-conditioning + whole home air purifier to central air system. I am told by the company that installed the air conditioning that the existing furnace and blower are more than powerful enough for the size of our home. Vaulted ceiling in the living room with only one vent, which is at the end of the duct work. Main supply duct has one register immediately above the unit with a register about 6 inches off of the main duct(which blows out an insane amount of air). It then continues up into the attic space and has 3 branches off of it, bathroom, guest bedroom and master bedroom- in that order, finally reaches living room vent. So largest room in house gets the least amount of air. Guest bedroom seems to get more air than master bedroom. Want to add more vents to system by adding mini ducts(to reduce the amount of remodeling work needed), but do not want to purchase the air handler for the system just the mini ducts. Was hoping to remove the main kitchen vent and install mini vents off of a branched 7 inch duct into the kitchen. Is this possible or do the mini ducts only function properly when used with the high velocity air handler?

  2. #2
    Join Date
    Jul 2009
    Location
    Northeast
    Posts
    661

    Default Re: Mini Ducts added to existing HVAC system

    Mini ducts are designed for high velocity systems because they are just that, high velocity which means they can push a lot of air through the mini ducts. I wouldn't try to use them on a conventional system because you would very little air from them.

    You don't say the size of your main trunk or the size of all your supplies, also the size of your return ,the tonnage of your A/C and BTU's of your furnace and blower size which is also measured in tonnage. All you say is your Town Home is 1300 sq ft. Way to little info.

  3. #3
    Join Date
    Jul 2010
    Location
    SoCal
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    5,438

    Default Re: Mini Ducts added to existing HVAC system

    You may have a sufficient A/C unit, with a poorly designed venting system. You mentioned that you have way too much air near the main, and too little far from the it. Ask the installer to redesign/replace the vents, ducts and registers to change that.

  4. #4
    Join Date
    Jul 2009
    Location
    Northeast
    Posts
    661

    Default Re: Mini Ducts added to existing HVAC system

    Before you pay good money to have your system redesigned try to damper down the supplies that are giving to much air while keeping the ones that aren't getting enough wide open. Most of the time it's just a poorly balanced system, Good Luck

  5. #5
    Join Date
    May 2011
    Posts
    251

    Default Re: Mini Ducts added to existing HVAC system

    Quote Originally Posted by dj1 View Post
    You may have a sufficient A/C unit, with a poorly designed venting system. You mentioned that you have way too much air near the main, and too little far from the it. Ask the installer to redesign/replace the vents, ducts and registers to change that.
    +1.

    It sounds like the ductwork wasn't properly sized and the duct balanced. It's a lost art. Companies just slap this stuff in, or many techs don't think doing the proper calculation (as recommended in their formal training) are nessesary.

    It would be like a carpenter refusing to use a pencil and tape measure and just eye balling everything.


    I might be possible just to add dampers and rebalance it. OR you could have the one branch to the end of the house enlarged.

    It's amazing what a couple dampers can do to rebalance a system.

    Worse, it's also possible your system is oversized. The more oversized a system is the worse the temperature imbalances will be. Bigger is never better in HVAC, it's always worse... and causes problems. I don;t know if yours is oversized, but it's estimated that over 50% of systems out there are oversized.

    My upstairs furnace is 2X the size it needs to be since it was likely sized using square footage, or the boiler size and & of radiators, rather than an actual load calculation.
    1925 Two-Story Stucco Beaux Arts Neoclassical

  6. #6
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    5,438

    Default Re: Mini Ducts added to existing HVAC system

    motoguy,

    You're right about the oversized a/c units.

    Kind like cars with 300+ HP - you can't afford getting caught over speed limit anyway, so why have the extra HP?

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