First and foremost thanks ahead of time for everyone's help :)

I am in the process of finishing my basement and had some questions/concerns about "what to do with the air" in my crawlspace. In my basement I have access to a conditioned crawlspace:

  • No venting to the outside
  • Cemented floor
  • Insulation (where insulation can be used)
  • Spray foam (where foam could be used)

I added a picture which shows a top level view of my basement. (Note: the drywall is not up yet but will be as soon as I figure this out).

The idea is I want to drywall the opening to my crawlspace and have one door which acts as the only entry point.

The crawlspace is fully conditioned and has an HVAC duct running through it which feeds other areas in the home. My question is what do I do with the airflow in this crawlspace?

  • Do I add a small vent from my HVAC duct to supply air from the HVAC system to the crawlspace?
  • Should I add a dehumidifier to be safe?
  • Where I am putting my drywall up to block off the crawspace should I add vent holes or anything?
  • Does the crawlspace need a return?

Side notes:

  • My crawlspace is ~1500sqft
  • Its located in Virginia
  • It has a interior french drain/sump pump installed (if that makes any difference)

Thanks everyone - I am by no means a professional so apologies if my terminology is off or incorrect.


2 Answers 2


Sounds a lot like my son's new house.

Since you already have an HVAC duct that runs through the crawl space just add a register to that duct. My guess is that unless you're actually going to seal the crawl space and make it air tight relative to the rest of the basement, you'll have enough leakage around the access door so that no additional return is needed.

I don't think the dehumidifier is needed with the air from the HVAC system. In my son's house, the crawlspace is open to the rest of the house. To be honest, it's a bit more than just a crawlspace in that the height is ~5 ft, but still with a concrete floor and insulated and sealed walls.

  • That works and makes perfect sense thanks :)
    – Andrew
    Jan 5, 2020 at 17:13

In most cases, you would have both a supply and return in the crawl. If the crawl is properly air sealed/encapsulated, then the air in the crawl should be the "same" as what is circulated in the home, so no issue with a return in there.

If it's not properly encapsulated, then I would take the steps necessary to do so before adding a return as you may introduce elements into the home from the crawl that you don't want. A return "may" not be necessary if there is enough air exchange through the door/wall adjoining.

I agree that a dehumidifier is likely not needed if properly encapsulated.

  • Thanks and makes sense
    – Andrew
    Jan 20, 2020 at 22:37

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