Set your basement dehumidifier to about 50 percent relative humidity. The EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent. A setting near 50 keeps most basements dry without running the machine nonstop. Then check the real number with a separate hygrometer to make sure it is keeping up.
By September, a lot of Ann Arbor basement dehumidifiers have been running hard for months. The bucket fills faster than you expected, the machine hums along in the corner, and you might not have looked at the setting since you plugged it in back in June.
The end of summer is a good time to check in on it. Basements stay humid well after the hot days fade, and a dehumidifier that is set too high, tucked in the wrong spot or quietly falling behind can let moisture build up without you noticing. A few small adjustments now can help keep your basement dry through the fall.
What humidity level should my basement dehumidifier be set to?
For most homes, a setting around 50 percent is a good place to start. The EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent. The EPA also says the key to mold control is moisture control, and in a basement, the dehumidifier is often your main tool for that.
Here is how to think about the setting:
- Around 50 percent. A practical target for most basements. It keeps you inside the EPA's ideal range without asking the machine to run constantly.
- Around 45 percent. Worth trying if your basement still smells damp at 50, or if you store boxes, fabric or furniture down there.
- Lower than that. Usually not needed, and the machine may run almost nonstop trying to reach it.
- 60 percent or higher. Too high. That is above the EPA's recommended limit.
One thing to know: the dial or display on many dehumidifiers is not very precise. A setting of 50 might hold the room at 50, or it might hold it a bit higher. That is why a separate hygrometer matters, which we cover below.
Where should I put my dehumidifier in the basement?
Placement makes a bigger difference than most people expect. A dehumidifier pulls in the air around it, so it works best where air can reach it from the rest of the space.
- Near the middle of the damp area. If the whole basement is open, a central spot lets it draw air from all sides.
- Away from walls and clutter. Leave open space around the intake and the exhaust. Check your owner's manual for the recommended clearance, since it varies by model.
- Close to where moisture shows up. If one corner always smells damp or one wall feels cool and clammy, put the unit closer to that side.
- Near a floor drain if you plan to use a hose. This makes continuous draining much easier.
- Off the floor in a damp spot if needed. A sturdy, level surface keeps the unit out of any small puddles and makes hose draining work better by gravity.
Keep interior doors to closed-off basement rooms open if you want the dehumidifier to cover them. A unit in the main room cannot do much for a storage room with the door shut. Also keep basement windows closed while it runs, so you are not pulling in humid outside air.
Should I empty the bucket or use a drain hose?
Both work. The right choice depends on your setup and how often you want to think about it.
- Bucket. Simple and works anywhere. The downside is that the machine shuts off when the bucket is full, and it stays off until someone empties it. In a humid stretch, that can happen more than once a day.
- Gravity drain hose. Many units have a fitting for a garden hose or a small drain tube. Run it to a floor drain or utility sink and the machine can keep running without stopping. The hose has to slope downhill the whole way.
- Built-in pump. Some models include a pump that pushes water up and over to a sink or out of the basement. This helps when no floor drain is nearby.
If you use the bucket, empty it as soon as it is full and give it a quick rinse with detergent and water now and then so it does not get slimy. If you use a hose, check it every so often for kinks, sags that hold water and a clear outlet at the drain.
How do I know my dehumidifier is actually working?
Get a hygrometer. It is a small, inexpensive gauge that reads humidity, and it gives you a second opinion on what the dehumidifier says.
- Place it away from the dehumidifier. Put it across the room or in the part of the basement that feels dampest, at about waist height. A reading right next to the machine will look better than the room really is.
- Give it a day. Let it settle in, then check it at different times of day.
- Compare the numbers. If the hygrometer reads close to your setting, the machine is keeping up. If it reads well above it, the dehumidifier is falling behind.
- Check after rain. Look again after a stormy day. That is when basements tend to get their most humid.
- Keep an eye on it into fall. Glance at it each week as the weather shifts so you can adjust the setting if needed.
What are the signs my dehumidifier is not keeping up?
Even a running dehumidifier can fall behind. Watch for these:
- The hygrometer stays above 60 percent most of the time, even with the machine set lower.
- The machine runs almost constantly and never seems to cycle off.
- The basement still smells musty after several days of steady running.
- Condensation shows up on cold water pipes, the inside of basement windows or the walls.
- The coils frost over. Some units ice up when the basement is cool, which stops them from pulling moisture. Many have a defrost mode, but frost that keeps coming back is a sign to check the manual or the unit.
- Stored items feel damp or cardboard boxes go soft at the bottom.
When a dehumidifier cannot keep up, the cause is often more water coming in than the machine can handle. The EPA advises that water seepage into basements should be stopped quickly so mold will not grow. Look for wet spots on walls or the floor, and make sure downspouts and grading are sending water away from the house. Also check your clothes dryer. The EPA recommends venting moisture-generating appliances like dryers to the outside, because an improperly vented dryer raises room humidity and may lead to mold growth.
Should I keep running my dehumidifier in the fall?
In many Ann Arbor homes, yes, at least into early fall. Basements stay cool and damp after summer, and fall storms can bring fresh moisture through foundation walls and floors. Turning the dehumidifier off on the first cool night can let humidity creep back up.
Let the hygrometer guide you. If the basement holds below 50 percent with the machine off for a few days, you can likely shut it down for the season. If the number climbs back toward 60, turn it back on.
A few fall tips:
- Clean the filter. Most dehumidifiers have a washable filter behind a front or side panel. Clean it with mild soap and water and let it dry fully before putting it back.
- Wipe down the bucket and housing. Use detergent and water, then dry.
- Watch for cold-weather icing. As the basement cools, some units struggle. Check the manual for the lowest temperature your model is designed to run in.
- Store it dry. If you put it away for winter, empty it, let it dry out completely and store it upright.
Basement dehumidifiers: myth vs. fact
Myth: Lower is always better, so set it as low as it goes.
Fact: The EPA's ideal range is 30 to 50 percent. A setting around 50 keeps most basements dry, and going much lower mostly makes the machine work harder.
Myth: If the bucket is filling up, everything is fine.
Fact: A full bucket means the machine is pulling water out, but it does not tell you if it is pulling enough. A hygrometer reading tells you if the room is actually dry.
Myth: A dehumidifier can fix a leaky basement.
Fact: It can lower humidity in the air, but it cannot keep up with water seeping through walls or floors. Stop the water first, then let the dehumidifier handle the air.
Myth: You only need a dehumidifier in the middle of summer.
Fact: Basements often stay humid into fall. Let a hygrometer, not the calendar, tell you when it is safe to shut it off.
Frequently asked questions
What humidity should a basement be?
The EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent. That applies to the basement too.
Should my dehumidifier run all the time?
It should cycle on and off once the room reaches the setting. If it runs nonstop for days, it may be undersized, set too low or dealing with a water source it cannot keep up with.
Is 55 percent humidity OK for a basement?
It is under the EPA's 60 percent limit, but above the ideal range of 30 to 50 percent. Lowering the setting a little is a good idea, especially if you store belongings down there.
What should I do if I find mold in the basement?
Fix the moisture first. The EPA notes that areas under about 10 square feet can usually be handled by the homeowner by scrubbing hard surfaces with detergent and water and drying completely. Porous items like carpet or ceiling tiles may need to be thrown away if they become moldy.
How Mold Medics Ann Arbor can help
If your dehumidifier is running all the time and your basement still smells damp, or you have found spots on walls, stored items or framing, we start with a free visual mold inspection. Using a thermal imaging camera and a moisture meter, we look for damp areas you cannot see and help you understand where the moisture is coming from. When remediation is needed, our 6 Steps to Victory process (Assess, Contain, Remove, Vacuum with HEPA equipment, Wipe Down and Anti-Microbial Application) handles the affected area, with HEPA air scrubbers running inside containment and anti-microbial applied with an electrostatic sprayer. If your basement is staying damp heading into fall, book a free visual mold inspection with Mold Medics Ann Arbor.
