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How do I Choose the Best Crawl Space Fan?

By Robert Partain
Updated May 17, 2024
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In order for to choose the best crawl space fan, you will need to do a bit of work before ordering the appropriate unit. You will need to make a visual inspection of the crawl space, measure the size of the area and determine what crawl space hardware will be needed to complete the job. Crawl space ventilation fans can be used in structures that have block, brick or concrete foundations. It will be important to choose the best unit that is designed for the type of foundation used in the home.

To complete the visual inspection, you will need to get under the house, with a flashlight, and look at the area. If the soil is damp, a moisture barrier of plastic sheeting should be applied as part of your project. Inspect the floor joist above your head to see whether water droplets are present. If they are, you have a severe moisture problem that can lead to rotting of the wood, mold and sagging floors if not corrected.

To choose the best crawl space fan, you will need to make an important calculation called cubic feet per minute (CFM) or cubic meters per minute (CMM). This is a measurement of how much air can flow in a predetermined amount of time. For crawl space fans, the time is 15 minutes, so it will measure how much air is moved during a 15-minute time period. To calculate the CFM or CMM that your crawl space fan will need, use the measurements of the crawl space to determine its cubic volume, then divide by 15. A fan with the correct CFM rating will be able to fill the crawl space with air in 15 minutes, or you might need purchase and install more than one crawl space ventilation fan in order to meet the minimum CFM or CMM rating.

In order the choose the best crawl space fan, you will also need to know what type of crawl space hardware will be needed to complete the job. These units can be either freestanding units or installed units. Freestanding units need no hardware other than an electrical outlet. Installed units should be used when the structure already has vent holes cut into the foundation.

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Discussion Comments

By Sporkasia — On Aug 30, 2014

Crawl space fans are like so many other things in life: It's better to have them and not need them than to need them and not have them. Having the fan is the best choice. Installing a crawl space fan is relatively simple and if nothing else, the fan will give you a sense of security.

In my opinion, the chance that a fan might keep my crawl space dry and keep termites from setting up their colonies is reason enough to invest in one.

By Drentel — On Aug 29, 2014

@Feryll - Good for you. You are lucky not to have had any serious moisture issues under your house. I'm guessing you live in a climate that has something to do with the lack of moisture. Still, don't make the mistake of assuming that because you don't have mold under the house everything is good.

This article mentions that sagging floors are sometimes a sign that you have a moisture problem, so you should keep an eye out for that. Moisture can also cause other problems. One of my neighbors has the exterminator out to his house regularly and the reason is that he has moisture under his house.

Insects and other bugs like dark damp places where they can hide and breed without worry. Crawl spaces are the perfect places in a lot of houses.

By Feryll — On Aug 29, 2014

Are crawl space fans needed for most homes? Am I wrong in thinking that most houses don't have crawl space fans and they do just fine without them? Our house is very old and when we had the crawl space inspected there were no problems with mold. The inspector actually said the ground was dry under there.

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