Basement Moisture: Everything Homeowners Need to Know
Part 5: Dehumidifiers — Do They Help or Hurt?
Just to get this out, I'm a pretty firm believer in dehumidifiers for basement health and comfort — when they are used correctly.
If you have a reasonably dry basement that is conditioned by your HVAC, I recommend using one in warmer months. That said, I do recommend some restraint in their use. Setting a unit to auto 40-50% humidity is reasonable. Setting your unit much below 40% humidity is not reasonable or recommended. A dehumidifier with an auto setting is a must, leaving a dehumidifier running non-stop 24 hrs a day is not recommended.
A major goal of dehumidifying a space is to prevent mold, fungus, and mildew growth. Let’s dig a little deeper into mold, for example. Ideal mold growth occurs at 70-90°F, but a space with poor airflow above 60°F with 50% humidity can slowly grow mold over time. Because most open areas in a basement generally maintain a temperature 70°F, targeting a humidity level of 40-50% can prevent most mold growth.
A common home dehumidifier.
When to use a dehumidifier.
In a space that is free of liquid water, over 60°F, and conditioned by your HVAC, it makes sense to use a dehumidifier. Consider, for example, an average height, 1800 sq. ft. basement at 70°F and 60% humidity. In these conditions, the air holds about 10 pounds of water. To get that under 50% humidity, you need to remove about 1 pound of water, or about 2 cups. A dehumidifier can increase home health and help prevent mold, fungus, and mildew growth, in a situation like this.
When NOT to use a dehumidifier.
You should not use a dehumidifier if your basement is regularly wet (as in standing or flowing water is common), if your basement is cooler than 60°F, or if it is winter (dry outside air). In these scenarios, the dehumidifier will have little noticeable impact. You will just be wasting energy. An unfinished basement can present many of these conditions and a common dehumidifier will do little to bring the relative humidity to a healthy level. It’s better to invest your resources in a solution that reduces the amount of moisture coming in.
Other Considerations
Down sides to dehumidifier usage include the following:
They will increase your electric bill with use.
They will produce a bit of heat (dehumidifiers use a condenser and refrigerant much like an AC).
They will need to be emptied daily (unless you set up a drain line from the unit to a suitable drain).
All things considered, I am a firm believer in the ability of dehumidfiers to add to the health and comfort of your home, given the right conditions.