Wet Crawl Spaces and Your Air Conditioner

Summer is quickly approaching and you will be turning on your air conditioning very soon if you haven’t already. We love our conditioned spaces but many people don’t consider how conditioning the living space affects the crawl space. In fact, most people don’t even consider the crawl space part of their home even though it has been proven the air in your crawl space is shared with your living space by up to 50%.

Crawl Space Mold and Soil Gases

If your crawl space is vented, like most are in America, the air inside the crawl space is affected by outside conditions like humidity, pollen and mold spores. When the crawl space takes on mold spores like stachybotrys or aspergillus, it can land on wood and other porous materials waiting for the right moisture levels to help it grow out of control. Wood rot fungus also likes to hang around until the right conditions are introduced. So what are the right conditions?

Mold Loves Moisture and Darkness

Crawl spaces are damp and dark so molds do very well in them. High humidity entering the vents in the foundation walls is a great way for mold to get a foothold on joists and sub-floors. Cardboard is another great food source and many homeowners like to store lawn mowers with grass clippings built up on the deck of the mower. Many harmful molds actually come from the soil so lawn mowers are great sources for toxic molds according to moldpedia.com. So what does this have to do with your home’s air conditioning unit in the summer?

Does My A/C Unit Make My Crawl Space Damp?

I have had many conversations with homeowners that claim to never have a mold problem and then all of a sudden, bam! One reason is upgrading from a very inefficient heat and air unit to a very efficient one may be the cause of increased humidity in a vented crawl space.

If you live in a home built 20 years ago and you go from a 10 to 20 year old HVAC unit to a 14 SEER system that blows cold air way more effectively than before, that cold air can affect the crawl space. We have seen homes where they upgraded the HVAC unit but not the ducts due to expense or maybe they were in good shape.

Ductwork Lifespan

Ducts installed 20 years ago have a different R value of insulation than today but even the R value installed today may not be effective at creating a thermal barrier between the warm summer crawl space air and the cold HVAC air. When a cold duct meets warm moist crawl space air, it’s like a cold glass of tea on a hot summer day. Sweating occurs on the ducts and that sweat evaporates and is absorbed by the surround insulation and wood.

Another reason we see crawl spaces explode with high humidity is if you take two identical homes and one home is kept on 74 degrees and the other is on 68 degrees, the home that is kept colder will condensate more in the crawl space if the HVAC ducts run through the crawl space. This is a shock to many homeowners. The best way to correct this is to install a dehumidifier to lower the dew point.

How To Stop The HVAC From Making Crawl Space Wet

The solution to fixing this problem is to control humidity which we would recommend a Hybrid Crawl Space Encapsulation System. Our solution does so much more than just control humidity.

Schedule Your Free Crawl Space Encapsulation Consultation

If you are looking for a worry free crawl space solution that addresses crawl space insulation, crawl space standing water, crawl space mold, crawl space humidity, crawl space vapor retarder and crawl space ventilation; ask about our proprietary Hybrid Crawl Space Encapsulation System.

Contact our team today!

8 thoughts on “Wet Crawl Spaces and Your Air Conditioner”

  1. My question is when this is completely done without any ducts or air conditioning under house should I be safe from mold forming ?

    1. Mold can form anywhere there is moisture or high humidity. Not having ducts does not limit mold from forming. Engineers in North Carolina did a study of crawl spaces with duct-work and mold was present. Hope that helps.

  2. I have a 14 seer ac installed. I’m having high humidity in the summer under the crawlspace…no ducting under there. It looks like the moisture is underneath where the return air is coming. My theory is the cold air swooshing over the wood floors into the registers is forming moisture on the subfloor. Is that possible?
    The rest of the house isn’t affected with cupping floors, just the rooms with the return air.
    Thinking of encapsulation or insulation.

    1. Hi Russ, there is a good chance the return duct is condensating and leaching moisture into the surrounding wood. I believe encapsulation with a dehumidifier to control the dew point would correct this. Hope that helps.

  3. Hi Michael
    I sure could use some help in determining the best way to spend my limited budget on resolving an indoor air quality issue. Since buying this home a year ago I’ve had sever allergy issues. I had an environmental company do a indoor air quality test and found elevated levels of Aspergillus. There’s no sign of mold on walls, ceiling etc so we believe it may be coming from HVAC / ducts which are located in the crawl space. Previous owners had it encapsulated but it’s not conditioned. There’s a dehumidifier down there as well. I’ve been told the encapsulation is a 5 out of 10 with workmanship. You can see daylight on one of the exterior vents. They cut a hole in the ductwork so it’s letting air in the crawlspace but it’s technically not conditioned. There’s signs of mold on the ductwork, insulation and the air handler. The “return” vent is running between the main floor joists and isn’t completely sealed so it’s bringing crawl space air into the system. I’ve never owned a home with a crawl space so I’m at a lost with what to do. I’ve had it “fogged” to kill the mold but I don’t think it was effective.
    Please help!!

    1. Hi Regina, I would recommend plugging all holes in ductwork that can be leaking or drawing air from the crawl space to the living space, get the mold on the outside of ducts and in crawl space removed and treated properly, and get the ducts and living space cleaned and sanitized if the high levels of aspergillus were found in the living space. Unfortunately none of what I described will be inexpensive and I don’t know of an inexpensive solution to addressing mold properly. Many people I speak with that choose less expensive options normally hire “professionals” that don’t know about mold remediation or the sequence in which to address the mold when located different parts of the home. The outcome is usually the same, they make the problem worse and even more expensive to correct. Hope that helps.

  4. Just installed an aprilaire E100 in crawl space.. will this help get rid of the musty, mildew odor coming from the vents into the house? Also, is it necessary to put vapor barrier down even with a dehumidifier?

    1. Most of the time it will not get rid of odors if the source of the odor is still present. Since musty odors come from mold and dehumidifiers don’t kill mold, it may still have an odor. A vapor barrier will help the dehumidifier run less.

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