Will a dehumidifier kill mold?

Mold Removal and Crawl Space dehumidifier Q&A


From: Fred

“I have a new addition to my home – about 1,900 sq ft of crawl space. The crawlspace is approximately 44″ high from the bottom of the floor joist to the top of the stone base floor. The crawl space is well vented with foundation vents and I have 6 mill visqueen plastic sheeting on the dirt floor covered with 4” of crushed gravel. I also have two sump pumps.

The problem is that during construction, the floor got wet and there is some white and black mold on the floor joist and the underside of the floor sheathing. My thought is to dry out the crawl space and the mold will go away before it gets too bad. Would a dehumidifier work for this problem or do I need to force some more air circulation under the house with fans?

Thanks for your help,”



Hi Fred,

Will a dehumidifier kill mold?

Getting the humidity under control will help your mold problem but not eliminate the mold all together. The mold will remain active as long as the humidity remains high usually 60% or higher.

Does a dehumidifier help with mold? Does mold die when it dries out?

If you lower the humidity with a dehumidifier to 50% and maintain it there, the mold will become inactive and not get any worse. However, it will not die, it will just be inactive and occasionally emit mold spores. For this reason, it would be beneficial to clean up the mold growth removal. There are several ways you can do this.

Does steam kill mold?

You can kill the mold with heat by using a vapor steam cleaner. It’d be best to use a dry vapor steam cleaner that heats at 180 to 220 degrees, which will kill most mold. Keep in mind, there are many different kinds of mold and some of them are heat resistant.

What are some non-chemical ways to kill mold?

There are three main options, first you can spray a solution of tea tree oil and water approximately 2 teaspoons to 2 cups of water. The only problem with this method is that the smell is very strong and tea tree oil is expensive but a little goes a long way.

Second, grapefruit seed extract or citrus seed extract and water can be used. You mix 20 drops of citrus seed extract with 2 cups of water and mix it in a spray bottle and spray on the problem areas. Do not rinse.

Or thirdly simply you can use straight vinegar in a spray bottle and apply it to the problem areas and do not rinse it. This is the cheapest method but like the tea tree oil the smell is very strong and might be around for a while.

US Steam White Tail US600 Vapor Steam Cleaner

I would caution you to be careful when doing mold growth removal. I recommend wearing a mask to prevent inhaling the airborne mold spores that will be present especially when you disrupt the mold. Also, you should isolate the area as much as possible so the mold spores cannot circulate to another area of the basement, where it could begin to develop in a new area.

In answering your question as to whether or not it is helpful to run fans, this is a good idea because when there is water in a liquid state, it will aid in the evaporation of the water; the increased humidity caused by the evaporation should be removed with a dehumidifier. In addition, mold likes a dark environment with no air movement, so circulating the air with fans is a great idea.

Keep in mind there are three things necessary for mold growth:

  • Mold spores — and there will always be a supply because it’s in the air outside and can easily infiltrate your home.
  • Porous surfaces for the mold to feed on like wood, wall board, etc. which we all have.
  • Moisture with humidity 60% and higher. (This is why eliminating and controlling moisture with a dehumidifier helps prevent the formation of mold. But do keep in mind that you’ll still need to remove any existing mold.)

Based on the dimensions you gave me, you would need to remove approximately 38 pints of moisture per day to maintain a relative humidity of 50%. You could consider the Pure & Dry HEPA 70 Dehumidifier and Air Purifier or the Frigidaire 70 Pint Dehumidifier.

Pure & Dry HEPA70 Dehumidifier and Air Purifier Combo

Besides a dehumidifier, another way to prevent mold from redeveloping would be to remove the mold spores that are airborne. This is normally next to impossible especially if there is mold already present in a particular area. However, assuming the mold in the area will be removed eventually this can be accomplished over a 4 week period through the use of an Airfree air sterilizer.

Airfree Onix 3000 Air Sterilizer
Airfree Onix 3000 Air Sterilizer
Read the reviews here!

The way it works is the mold spores enter the air sterilizer through convection where they go into a chamber where they are incinerated at 400 to 600 degrees. The air is then cooled and the sterilized air is emitted back into the room. Slowly over time the amount of mold spores in the air will be reduced down to zero and by leaving the unit running continuously, any new mold spores introduced into the air will be removed. The net result is if conditions arise to encourage the formation of mold like water or excessive humidity, mold will not develop because you have removed one of the three things necessary for mold to develop. In your case, you would need 2 of the Airfree air purifiers because one of these units will sterilize an area of 450 to 650  square feet with a ceiling height of 8 feet, which is 3600 to 5200 cubic feet. You have approximately 7600 cubic feet so 2 units would be recommended. The nice thing about the Airfree is it is completely quiet and there are no filters to change and zero maintenance. The electrical usage is like a light bulb so it might cost you a couple of dollars a month to run one of these.

One final note, I failed to mention to you that the most important thing to do when you have mold is to consider the source of the mold to begin with and make sure the reason for the mold occurring in the first place has been remedied. It sounds like you have already taken care of this based on the fact the mold was a result of water leaking during construction.

Our page about Mold Solutions can also provide additional information on mold removal.

Please feel free to contact me to discuss any of the products we offer from AllergyBuyersClub.com