Having a dehumidifier with a wrong setting can be just as useless as having no dehumidifier.
Even before you buy a dehumidifier, it makes sense to educate yourself about relative humidity levels. The basic idea is to keep indoor relative humidity between 30% and 50%.
However, when it comes to basement dehumidifier setting, we’re sometimes perplexed – should be set the dehumidifier to 30%, 40%, 50%, or even 60% relative humidity? This is especially important when figuring out the correct dehumidifier setting to prevent mold and mold growth.
Under ‘Mold Course Chapter 2’, in the 3rd Lesson – Humidity, EPA clearly states the following:
Sometimes, humidity or dampness (water vapor) in the air can supply enough moisture for mold growth. Indoor relative humidity (RH) should be kept below 60 percent — ideally between 30 percent and 50 percent, if possible. Low humidity may also discourage pests (such as cockroaches) and dust mites.
- Damp environment. Example: Basement with 80% relative humidity.
- Hot environment. The hotter the indoor is, the more likely it is for the mold to flourish.
That means that we have to be aware of the basement temperature and the relative humidity. In the end, you’ll find the commentary for 30%, 40%, 50%, and 60% relative humidity setting.
What Relative Humidity Dehumidifier Setting Is The Best For Mold Prevention?
- Below 65%. According to Portland State University’s article, citing Canada Mortgage Housing Corporation publication.
- Between 30% and 60%. According to Aspen Environmental Services.
- Below 75%. According to ‘Humidity Requirements for Mold Growth‘ article by S. S. Block, working at the Department of Chemical Engineering, University of Florida, in 1953.
In short, there is no clear answer.
Most HVAC engineers, however, agree that the most appropriate basement dehumidifier setting is 40%.
It might be that 50% would be enough. However, at higher temperatures such as 80°F or 90°F, the likelihood of mold growth is significantly increased. To negate this, it’s always safer to set a dehumidifier setting to 40% to prevent mold growth.
Obviously, the basement dehumidifier setting of 30% would be the safest but not the most energy-efficient. If the 40% basement relative air humidity can guarantee the absence of mold growth, all the electricity needed to bring relative humidity from 40% to 30% would be wasted (or would be of no consequence as far as mold growth is concerned).
Here is the full list of basement dehumidifier setting options with commentary:
- 60%. Too high; mold might grow.
- 50%. Not safe enough; at high temperatures, there might be a minimal change of mold growth (usually localized to a corner).
- 40%. Just perfect; very safe with no chance of mold growth.
- 30%. Needlesly low, you will waste energy to reduce humidity from 40% to 30% without increasing anti-mold safety.
What is “Unneedlessly Low” haha. Sorry, I just felt an unneedless desire to comment, because it made me laugh. But I understood the intended meaning! Thanks for the help!
Haha made us chuckle a bit as well. Fixed now 🙂
Thanks for the info! Here’s a couple of other things that may bring a chuckle or two.
Our old dehumidifier had a bucket that needed to be emptied daily, so either my wife or I would empty it when we noticed it wasn’t running. For over a month, both of us assumed the other had emptied it when in reality, it just wasn’t working – the bucket was bone dry and probably had been for weeks!
When I read on you site the recommendation of “most HVAC engineers,” I again had to laugh at myself. My son-in-law has been in the business for years and owns an HVAC company. I could have just asked him!
My grandson has a dehumidifier set on 90 in a really damp basement…is this set right…
Hello Veronica, 90% relative humidity is way too high. That’s close to 100% humidity. Try setting it to at least 60% or lower.
We recently purchased a dehumidifier for our basement and have been running it non-stop on the highest setting for several days now. However, for whatever reason the humidity never seems to drop below 50%. Is there a reason why this might be happening? Thank you!
Hello Trisha, the dehumidifier you have appears to be undersized a bit. It doesn’t seem to have enough pint capacity to handle all the moisture load in your basement.
What should I set my dehumidifier on in a crawl space winter an summer? Should i use the dehumidifier in winter?
Hello Darryl, anything below 60% should be ok. You can set it to 50% in a crawl space. If the humidity rises above 60%, it makes sense to use dehumidifier in a crawl space in the winter as well.
Many dehumidifiers do not have settings below 50 percent. I live in Southern Ontario. Generally on the humid side due to the Great Lakes. I have a finished basement and set my humidifier at 50 percent. Anything higher than 60 and you begin to smell must.