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Actively condition the encapsulated crawl or just run a humidifier?

StevenNC8b | Posted in General Questions on

My HVAC sub advised against any part of my system venting into the crawl. I have heard that some have vents into their crawl. I do plan on having a dehumidifier. What are your thoughts about the HVAC? And if it is or isn’t vented into the crawl… What are your thoughts about whole house humidifiers/dehumidifiers built into the HVAC system itself?


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  1. Expert Member


    The ways we are allowed to deal with sealed crawlspaces here are:

    1. Connect the space with the house above with vents, the size of which is determined by the area of the crawlspace. You might call this a passive approach. It is simple, but means you share air with what is never that clean a space, and it encourages the stack effect.
    2. Install an exhaust fan to outdoors, and have a floor vent from the house above as supply air. This has the advantage of creating some negative pressure, keeping crawlspace air out of the house above, and providing heat.
    3. Integrate the crawlspace into the mechanical ventilation of the house as just another room. I can only see a problem with this approach if it is connected with your heating system, and some return air would go back into the house. If you were using a dedicated ventilation system - say an ERV - I don't see any negatives.

    I don't think a whole house dehumidifier would be a good idea, as it would rely on recycling the crawlspace air.

    Whether you rely on a dehumidifier, or ventilation to control excess moisture, you are going to need a heat source down there too.

  2. user-5946022 | | #2

    So many things factor into this.
    How much, if any, of your crawl is below grade?
    - If 1/2 or more of your crawl is below grade, the crawl will be more apt to maintain an appropriate temp.
    Where is your HVAC equipment?
    - If your HVAC equipment is in the crawl, even if it is tightly sealed, it will leak sufficiently to condition the crawl.
    What part of the country are you in?
    - In some areas, such as the SE, you probably need a dehumidifier. In other areas it may not be needed.
    Even if you have a dehumidifier, you probably need to actively move air around the crawl. Thus, a dedicated dehumidifier ducted throughout the crawl will help you move air around. Based on experience, duct it to near the perimeter of the crawl

  3. StevenNC8b | | #3

    I am located near Charlotte NC Almost all of the front of the crawl is below grade but the back is kind of like a walk out basement with 8 foot wood framed walls. It is tall enough that I was able to put a normal exterior door as the access. HVAC equipment will be located in the crawl.

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