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How to add a whole house dehumidifier to a ductless minisplit setup?

Mixed_Beans | Posted in Mechanicals on

I am planning out a new home build and we are thinking that it might be best to go with ductless mini splits for the heating and cooling needs. While I know many mini splits can dehumidify it seems it would be much more effect, for whole house de-humidification, to have a stand alone dehumidifier. What I am trying to figure out is how you do this? I believe dehumidifiers are usually connected in-line with ducted heating and cooling but what do you do with ductless heating and cooling?

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  1. walta100 | | #1

    The title asks about humidifiers and the question is about dehumidifiers, that is confusing.

    Standalone dehumidifiers fall into one of two types portable units made of plastic that tend to fail just after the one-year warranty expires or large expensive units.

    The way I see it dehumidifiers are super-efficient space heaters with a COP over 1.

    In most locations a correctly sized AC unit will remove enough moisture to make your home comfortable.

    If you live in a swamp and the outdoor temp is relatively close to your indoor set point much of the time and your AC unit is oversized then dehumidifiers would make sense.

    Matt Risinger on YouTube seems to live in a place where dehumidifiers are necessary and you may find what he has to say interesting.


    1. Mixed_Beans | | #2

      My mistake. I fixed the title.

      You referenced AC systems. I assume you mean central air. This won't be a central air situation but instead a number of ductless minisplits. While the do dehumidify it doesn't make sense to be running them all the time to keep the humidity down. Then there is the question what you do in the Winter? You won't be running AC but still need to handle any humidity created by daily living (showers, cooking, breathing, etc). I suppose the ERV could handle some of this but can it handle all of it?

      I'll rewatch Matt's video. I don't recall ever seeing a ductless build of his. Usually he has some type of air handler with the dehumidifcation inline but maybe I missed this video.

  2. walta100 | | #3

    High indoor winter humidity is generally not a problem unless the house is crazy tight and then you have an ERV power venting the house expelling moist air and bringing in dry air.

    Moisture tends to distribute its self pretty evenly so long as the temp is pretty much the same, so I dont see the minis as a problem.

    Note Matt must have a dozen or more dehumidifier videos.


  3. tim_in_nc | | #4

    We installed a whole-house dehumidifier (Santa Fe UltraAire 70H) this past winter after a few years of experiencing high indoor humidity during shoulder seasons in our house, when it was humid outside but not hot enough to run the AC constantly. Worked like a charm.

    I was also really struggling about where/how to install it, and ended up putting the unit itself sitting on the floor in a closet, running a small length of insulated flex duct to a new exhaust register running out through one of the closet walls into our living room, and then putting a Tamarack return air pathway in another of the closet walls to pull in fresh air from a different room. I was worried about maybe needing more ducting , but like Walta says, humidity distributes itself pretty quickly throughout a house, so that's been fine. We have it on an ESPHome minicontroller I built that triggers it on or off based on the whole-house average dewpoint, which is something you'd have to DIY. Just having the unit inside a closet is enough to mitigate the noise. And our cats love to nap right in the path of the exhaust when it's blowing out warm air.

    For a new build, you might think about just leaving space in a closet or basement area to install a unit, making sure you can run an intake and exhaust duct into the conditioned space of the house and have a drain pipe close enough that you can run a line from the dehumidifier condensate pump. That will allow you to see whether you actually need the extra dehumidification.

    1. Mixed_Beans | | #5

      Ok. Sounds like we wouldn't need a lot of duct work then for a 3 floor house. If we don't put one in right away maybe it is worth to at least get ducts in planning for it. Of course this depends on whether or not we need it. The house is being built pretty tight minus a potential pivot front door.

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