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V5Farm | Posted in Energy Efficiency and Durability on

Got a question…if on average, the unfinished attic has higher humidity than the livable space, should I vent the dehumidifier into the attic, vs. ducting it into the supply of the HVAC?

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  1. Trevor_Lambert | | #1

    I'm confused by the terminology "vent into" and "duct into", and judging by the lack of responses to an otherwise simple question, I guess I'm not the only one.

    As far as I know, there's only two types of dehumidifier, one with with an inlet and outlet for ducting, and one that takes in ambient air and just spits it back out to the same space. For either one, the incoming and outgoing air have to be balanced. You can't pull air from the main house and vent it into an unconditioned attic, because you're depressurizing the house. I can't think of a reason why you'd want to in any case, because you'd also be raising the humidity inside the house (assuming it's humid outside, otherwise why have the dehumidifier at all?).

    So, by "unfinished" do you mean it's currently unfinished but is within the conditioned enveloped, or is outside the envelope? If it's the latter, you don't want to connect it in any way to the rest of the house.

  2. Jon_R | | #2

    Assuming humidity conditioned space - yes, you should attempt to apportion delivery of dehumidified air to where it is most needed. Also note that this can change significantly - imagine a home where an easterly wind is causing almost all of the infiltration to be on the east side. Then the wind switches to the west.

    Maybe someday homes will be designed to fully manage temperature, humidity and IAQ on a room-by-room basis.

  3. V5Farm | | #3

    Thanks Trevor and Jon, sorry for the brevity, was running late...but to further describe, yes the entire house is encapsulated with foam, and the upstairs is unfinished. “Vent and duct” I was using interchangeably. Currently I have an Ultra Aire XT105H with a dedicated return ducted from the livable space downstairs, and the dehumidified air ducted into the supply side of my central HVAC. My problem is that it seems to be fighting with my Trane variable speed HVAC, in that once the humidity set point has been exceeded the Dehumindifier kicks in and sends warm dry air into the supply, which is cold because of a cooling cycle, so then a humidity spike occurs send the humidity up about 8% and then the AC kicks in and in combination with the Dehumindifier eventually brings the humidity back down. So I thought since the upstairs/unfinished attic has on average about a 3-5% higher humidity, I would re-duct the Dehumindifier to send dehumidified air into the unfinished space?

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