How to Check a Dehumidifier After Winter Storage

Why a post-storage check matters

Dehumidifiers spend months idle in attics, basements, or closets. During that time, dust settles on the coils, the filter can collect debris, and moisture may accumulate inside the unit. Mold can grow wherever there is moisture, and the EPA notes that mold can begin growing on damp surfaces. Checking the unit before you plug it in helps you avoid pushing mold spores into your living space and ensures the dehumidifier works efficiently.

If you stored the unit with water left in the bucket or drain pan, there is a higher chance of microbial growth. The CDC recommends keeping indoor humidity below 50% to prevent mold. A thorough inspection is the first step to keeping your home dry and healthy. For guidance on avoiding storage mistakes, see our seasonal storage advice.

Inspect the coils

The coils are where moisture condenses. Over time, dust and grime can coat the fins and reduce airflow. Look at the evaporator coil (the one that gets cold) and the condenser coil. If you see frost or ice, let the unit thaw completely before cleaning. Use a soft brush or a vacuum with a brush attachment to remove loose dust. For stubborn dirt, follow the manufacturer's instructions or use a coil cleaner that is safe for the finish. Avoid bending the fins.

Check for any signs of corrosion or refrigerant leaks, such as oily spots or a hissing sound. If you notice bent fins, a fin comb can straighten them, but do it carefully. For a deeper clean, see our guide on cleaning evaporator coils without removing them.

Check and clean the filter

A clean filter is essential for proper airflow. A clogged filter makes the unit work harder and removes less moisture. Remove the filter according to the manual. If it is washable, rinse it under warm water and let it dry completely before reinstalling. If it is disposable, replace it with the same type. While the filter is out, wipe the surrounding area to remove dust.

The filter is the first line of defense against particles that can coat the coils. If you are unsure whether your filter is reusable, check our guide on washable vs. replaceable filters.

Inspect hoses and the drain system

If you use a continuous drain hose, inspect it for cracks, kinks, or blockages. The hose should slope continuously downward to allow water to flow by gravity. Disconnect the hose and blow through it or run water to clear any obstructions. Check all fittings for leaks. If the unit has a pump, inspect the pump inlet and outlet for any debris. Also, check the bucket and the float switch that signals when the bucket is full. Clean the bucket with mild soap and water to remove any residue.

A blocked drain is a common cause of leaks and overflow. For step-by-step help, see our hose clog clearing guide and our drain hose leak test. If you need to refresh the bucket, follow our bucket cleaning and odor removal routine.

Check controls and do a test run

Before committing to a full season, plug the unit in and run a short test. Set the humidity toggle to the recommended level, usually between 30% and 50% for comfort and mold prevention. Listen for unusual noises and make sure the fan and compressor come on. After a few hours, confirm that the bucket or drain is collecting water. If the display shows an error code or the unit does not start, consult the manual or contact the manufacturer.

Also consider the operating temperature. The ENERGY STAR site notes that some dehumidifiers are not designed to work efficiently below 65 degrees Fahrenheit, so if the room is colder, you may need to wait or use a low-temperature model. Review our first-run guide and troubleshooting for a unit that won't turn on if you encounter problems.

Clean away mold and musty odors

If you spot mold on the exterior, bucket, or drain pan, clean it before running the unit. The CDC recommends a bleach solution of no more than 1 cup of household bleach in 1 gallon of water for hard surfaces. Wear rubber gloves and eye protection, and never mix bleach with ammonia. For the interior, use a damp cloth with a mild detergent. Allow all surfaces to dry completely before reassembling. If the unit smells musty even after cleaning, check the filter and coils again.

The University of Minnesota Extension also suggests scrubbing moldy surfaces with a stiff brush, hot water, and a soap that does not contain ammonia, then following with a bleach disinfection step. For a complete cleaning routine, see our disinfecting and mold removal guide.

Prepare for the first run

After moving the unit from storage, let it stand upright for at least a few hours. This allows the refrigerant to settle and prevents compressor strain. Inspect the power cord for damage and make sure the plug is clean. Place the dehumidifier on a level surface with at least a foot of clearance on all sides for airflow. If you have a pump model, prime the pump according to the manual before starting. Also, ensure the humidity sensor is not blocked; a dusty sensor can give false readings.

For placement guidance, see our placement tips. If your unit has a condensate pump, follow the pump priming steps to avoid air locks. Once the unit is running, you can monitor performance using a hygrometer and adjust as needed.

What to pick for your use

Questions

How often should I check my dehumidifier after storage?

At minimum, perform the inspection before the first use of the season. If the unit sits unused for several months, a quick look at the filter and coils can prevent performance problems.

What should I do if I see mold inside the unit?

Clean the affected surfaces with a mild detergent or a bleach solution as described in the CDC guidelines. Wear protective gear, and never mix bleach with ammonia. Dry everything thoroughly before reassembling.

Can I use bleach on the coils?

It is safer to use a mild detergent or a dedicated coil cleaner. Bleach can damage the coil finish and may void the warranty. Follow the manufacturer's instructions.

How long should I let the unit sit before turning it on after moving it?

Allow at least a few hours for the refrigerant to settle. Some manufacturers recommend up to 24 hours for models with compressors. Check the manual for specific guidance.

Is it safe to use a dehumidifier that was stored in a cold garage?

If the unit was exposed to freezing temperatures, inspect it for ice and let it warm up to room temperature before running. The ENERGY STAR site notes that some units are not designed for temperatures below 65°F, so check your model's specifications.