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Thread: Adding AC to existing baseboard heated home

  1. #1
    DIY Junior Member martyd's Avatar
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    Default Adding AC to existing baseboard heated home

    We are starting to investigate adding AC to our home in CT. I'm learning as we go along about this type of installation with compressor on the ground and air handler in the attic. One of the companies said they do not install an outlet in the bathrooms due to mold problems. It kind of makes sense since the system will be off for about 8 months and I suppose moisture could leak into the cold duct. He assured me that enough cool air would be present in the baths.
    Any comments on this? Is it a common practice? Thanks, Marty

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Depending on the layout of the house, instead of trying to retrofit ductwork, you might want to look into minisplit systems. Those come in many different configurations, some of which allow ducting to spaces you may not want a head in (like a bathroom), and, many of them are quite efficient. Second benefit, all of them are available as a heat pump, and can serve as a heat source, too, for not much more cost than an a/c only version. They would provide zoning, which may be harder to obtain with a ducted system, and other benefits as well. There has been a lot of discussion on this topic, so you might want to read a few of those threads, then come back for more specific questions to your situation.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    In the trades Dana's Avatar
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    What Jim said.

    Putting ducts & air handler in the attic is a common practice, but i'ts an actively BAD idea even in warmer climates, but in CT punching a bunch of large holes in the ceiling is an air-sealing nightmare, and you end up with more wintertime air infiltration resulting in higher moisture levels in the attic, and bigger heating bills to boot. And when operating the air handler drives pressure differences between rooms that increase infiltration rates orders of magnitude beyond natural stack-effect leakage, and even if you had perfectly balances perfectly sealed ducts the direct heat gain of being located in the attic typically adds a full ton to the peak cooling load.

    Ductless heat pumps only make holes in walls/ceilings big enough to run the refrigerant lines & control/power cabling and condensate drain through- it's typically done with a single 3" conduit through the wall that can be readily air-sealed. The ductless head takes and delivers air only from the room where it is location, with effectively zero infiltration drive, and the hottest environment the refrigerant lines see is the outdoor air, not a 130F attic.

    And they're fully modulating systems with a 3:1 or better turn down ratio- making them quieter than any ducted solution, with much stabler air temps.

    In heating mode better-class mini-splits hit geothermal heat pump type efficiency in a CT climate, and guaranteed to be cheaper than heating with oil or propane at any efficiency, and comparable to heating with mid-efficiency gas boilers. But during the shoulder seasons when it's over 40F outside it's cheaper than heating with condensing gas.

    But all cooling or heating solutions start with calculating the loads at the 1% and 99% outside design temperatures. Any HVAC contractor that doesn't provide the room-by-room load calculations isn't worth considering (unless YOU do the math, and are directing THEM, which is what I've had to resort to.)

    [edited to add]

    If you're going for a ducted solution, putting the ducts in a basement is always going to have fewer issues than putting them in an attic. While you get better mixing of the cooling air with the room air with ceiling-mounted ducts than with floor mounted ducts (due to the higher density cool air seeking the floor), that doesn't make up for the shortcomings of installing them in an unconditioned unsealed attic.
    Last edited by Dana; 10-24-2013 at 10:04 AM.

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