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Should I Make A Hole in the Foundation to Dry A Small Crawl Space

Should I Make a Hole in the Foundation Wall to Dry a Small Crawl Space add-on that was built and make sure the space is properly ventilated? I have a small 11x14 foot crawl space that is sealed and unvented. The crawl space is separated by a foundation wall from the larger crawl space. I am laying vapor barrier in the small crawl space and believe I need a dehumidifier for that space as well. I am wondering if you think it best to:

  1. Punch a hole in the foundation and run a duct kit from the current larger crawl space dehumidifier into the smaller one?
  2. Get a separate smaller dehumidifier to keep the small crawl space dry?
  3. Other suggestions?

If you suggest a separate smaller crawl space dehumidifier, do you recommend a make or model for a 250 square feet area?

Q: Punch Hole in Foundation and Run Duct Kit

A: This is a great idea if you are wanting to move dry air from one part of your crawl space to another. Make sure if you decide to punch a hole in the foundation wall you do not destroy the walls integrity. The ducting of the whisper fan is 4-inches and can be easier to install. Making a hole for this type of ducting can be accomplished with a 4.25"x11" masonry drill bit hole saw. Drilling a hole is much easier than cutting a square in my opinion to push dry air from the crawl space dehumidifier.

The drawback you need to prepare for is the fan is running continuously so choose an energy efficient model. The fan will need to push moist air from the small crawl space to the larger area where the dehumidifier is located. You may need to drill a secondary hole for the air to move from the small to larger crawl space. If there is no pressure release from the fan blowing into the small crawl space it's like you blowing into a 2-liter soda bottle. Pressure builds and no more air can enter.

Q: Install a Smaller Crawl Space Dehumidifier

A: This is a great option as well but maintaining two dehumidifiers can be a little more work than one dehumidifier and an exhaust fan. The small crawl space may also need an exhaust fan with a small dehumidifier if there is a chance for harmful soil gases to build up. Then you have another dehumidifier and foundation vent fan. If you are looking for a small crawl space dehumidifier that does about 250 square feet your choices are limited to cheaper units. You will also need a condensate pump built-in or have an exterior one to drain into. Many online dehumidifiers are not very energy efficient and are rather tall for small crawl spaces.

Q: Any Other Recommendations

A: Another option is to install a foundation vent fan in the small crawl space exterior wall and blow air out. You will also need to make a hole in the interior wall between the small and large crawl space. If you use the Lomanco PCV-1 style fan you will need no ducting. The Lomanco fan is very energy efficient. It will remove soil gases as it draws dry air from the large crawl space. No matter which route you take, I recommend a humidity reader to monitor the small crawl space.

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About Michael Church

Michael Church has been involved with indoor air quality since 2005 and feels the unhealthy crawl space is one of the major problems causing poor indoor air quality.


  1. Lee shay on May 5, 2023 at 1:56 pm

    I need your help. We hired a. Reputable company do install an drain system, a second sump pump and encapsulation. We paid $22,000. We were please except for the strong fumes coming into our living area. They used Butyl caulking. It has been 11 days we have been inhaling these fumes. They advice they are not toxic but I read they are. Today they have installed an exhaust fan. Why are these fumes so strong? Should we be concerned about the continual inhalation? Thank you

    • Michael Church on May 19, 2023 at 9:05 pm

      You may want to find out what type of caulk they used and contact the manufacturer or get them to supply you with the SDS. We make SDS available for our products.

  2. James on August 7, 2023 at 7:59 pm

    Do you sell the crawl space.jacks for support.

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