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Problems Using Dehumidifiers in Crawl Spaces

The Common Fallacies, Challenges, and Problems with Using Dehumidifiers in Crawl Spaces.


I did an inspection last week inside the crawlspace on the south side of Charlotte, NC where I discovered that the homeowner had sealed off all of his vents, and installed a commercial dehumidifier inside the space in an attempt to mitigate crawl space moisture. As it was a winter inspection, it was not surprising to find that the wood moisture content of the floor members inside the crawl space to be only 4%. This is extremely low. The ideal range is 12-14%.  The customer was complaining of cracks in his hardwoods, as well as minor sheet rock cracking above load bearing walls, stairwells, and doorways.

The dehumidifier was running at the time of the inspection. The dehumidifier is a relative humidity controlled device, and becomes less accurate in cooler temperatures. The unit was set at 50% RH with the temperature inside the crawl space at a mild temperature of 55°F. 4% wood moisture is way too dry. There is no doubt with these low moisture readings combined with the symptoms reported by the customer that there were no major structural deficiencies,  but in fact the result of the wood members becoming too dry from excessive dehumidification causing severe shrinkage of the wood members supporting the floor system.

During the inspection, the dehumidifier was reset to operate as efficiently as it can in a winter setting. This will save the customer $20 a month on the electric bill. There is no reason for a dehumidifier to be running in the winter time in most situations. Companies that install sealed crawl spaces and/or closed crawl space systems relying completely on a dehumidifier may be causing homeowners to have damage to their floor systems. Often technicians whom install the dehumidifier set the units to their driest settings with the agenda of running the unit harder so it will burn out and require replacement often just a few months after the manufacturer’s warranty has expired. Dehumidifiers are expensive and they use excess energy. Especially during the winter months when the moisture levels are lower and dehumidification is unnecessary.

Key Points for Crawl Space Dehumidifier Use

  • Dehumidifiers are not designed to run efficiently inside crawl spaces.
  • Dehumidifiers are energy hogs causing power bills to rise $20-40 per month.
  • Dehumidifiers are humidistat controlled devices that are ineffective during the winter months.
  • Dehumidifiers can cause the wood members inside the crawl space to get too dry causing shrinkage symptoms to be observed in the upper areas of the home.
  • Dehumidifiers need to be replaced often. Commercial units cost $1500.
  • Encapsulated or Closed Crawl Spaces combined with dehumidification cause the buildup of stale air creating poor crawlspace air quality for the entire whole house envelop. Odors and smells from the off gassing of construction materials, plastic liners, and the soil are often reported by customers.
  • HVAC Systems utilizing natural gas require expensive modifications to meet code requirements inside encapsulated crawl spaces.


These are just a few of the concerns that you should be aware of. The good news is there are alternatives to solving these challenges such as the integration of controlled ventilation systems that can often eliminate the need for dehumidifiers completely.  For more information on newer and more relevant technologies please don’t hesitate to reach out to us for more information….. Call Masserang Consulting at (704) 787-6972

Remember. Don’t Encapsulate! Ventilate!


I reached out to Michael for consultation services and he was one of the most helpful small business owners I have ever encountered. His subject matter knowledge was surpassed only by his willingness to help me solve my problems. I would highly recommend his company to anyone seeking help or services with their foundation, basement, or crawlspace – you dont come across good folks like him very often! Thanks, Michael.

S. Kelly
Google 5-Star Review

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