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Dehumidifier Smells Musty? Clean the Bucket, Coils, and Filter

Standing water and a damp filter grow mildew inside a dehumidifier. A vinegar wash clears it, and cleaning tablets help keep it from coming back.

By Jamilur Rahman Updated November 5, 2026 · 6 min read

Time
30 min, plus drying
Cost
Under $20
Difficulty
Easy
A portable dehumidifier on a basement floor with its water bucket pulled out beside it, next to a soft brush and a bottle of white vinegar
In this guide
  1. Quick answer
  2. Free vs. permanent fix
  3. What you'll need
  4. Why it happens
  5. Try this first (free)
  6. When free fixes aren't enough
  7. Buy the fix
  8. Put it away clean at the end of the season
  9. What to skip
  10. FAQ
  11. Related problems

Quick answer

When a dehumidifier smells musty, mold and mildew are growing on the water bucket, the filter or the coils, usually because water sat in it. Unplug it, wash the bucket with soap, soak it in half vinegar and half water, rinse and dry the filter, and brush dust off the coils. Cleaning tablets in the bucket help keep the smell from returning between cleans. They are a helper for people who would rather not scrub every two weeks.

Free fix vs. permanent fix

Free fix · 30 minutes, plus drying

Wash the bucket, filter and coils

  • Unplug the unit and empty the bucket
  • Wash the bucket with soap, then soak it in half vinegar and half water
  • Rinse the filter and let it dry fully
  • Dust the coils with a soft brush or vacuum

How long it lasts: Clears the smell right away. It comes back in a few weeks if water sits in the bucket or the filter stays damp.

Most readers choose Permanent fix
Dehumidifier cleaning tablets (illustration)
Illustration

Dehumidifier cleaning tablets

Tablets made for dehumidifier buckets and drain pans dissolve in the water the machine collects and slow the growth of slime and mildew. The wash clears today's smell. The tablets help stop it coming back, which is the step most people skip.

How long it lasts: Used as the label says, they help keep slime and mildew from forming between cleans. They do not replace the wash.

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As an Amazon Associate I earn from qualifying purchases.

What you'll need

  • Soft brush or old toothbrush

    For the bucket corners and the coils

    You have it

  • White vinegar

    Mixed half and half with water

    You have it

  • Vacuum with brush attachment

    For dust on the filter and coils

    You have it

  • Garden hose or drain hose

    Continuous drain means no standing water in the bucket

    You have it
  • Our pick
    Dehumidifier cleaning tablets (illustration)
    Illustration

    Dehumidifier cleaning tablets

    Drop one in the bucket as the label says

    Check price
  • Replacement filter for your model (illustration)
    Illustration

    Replacement filter for your model

    Only if the filter is stained, brittle or still smells after cleaning

    Check price

Why it happens

1

Water sitting in the bucket

Standing water is where mildew and slime grow. A bucket left full or damp for days can smell within a week or two in a warm room.

2

A damp, dusty filter

The filter catches dust, and the moist air passing through keeps it damp. Dust plus damp grows mildew, which blows musty air back into the room.

3

Dust and film on the coils

The coils get cold and wet as they pull moisture from the air. Dust on them turns into a damp film where mold grows.

4

A kinked or slimy drain hose

If you use a hose for continuous drain, a kink or a slimy buildup can leave water standing inside it.

5

The smell is in the room

A dehumidifier pulls in the air of a damp room. If the basement smells musty, the machine can seem to smell the same. Clean the machine first, then fix the damp.

Try this first (free)

Do these in order, starting with the simplest.

  1. Unplug and empty it

    Unplug the dehumidifier and pour out the bucket. Take out the bucket and the filter. Your manual shows how.

  2. Wash the bucket

    Tool used: White vinegar

    Scrub the bucket with warm water and dish soap, including the corners and the float. Then fill it a quarter full with equal parts white vinegar and water, slosh it around and leave it 15 to 30 minutes. Rinse well. Never mix vinegar with bleach.

  3. Clean the filter

    Tool used: Vacuum with brush attachment

    Vacuum the dust off the filter, or rinse it under the tap if the manual says it is washable. Some filters cannot be washed. Let it dry completely before you put it back, since a damp filter regrows mildew.

  4. Brush the coils

    Tool used: Soft brush or old toothbrush

    With the unit unplugged, brush dust off the coils gently. The fins are thin and bend easily, so brush with the fins, not across them. Wipe the inside of the housing with a cloth dampened with the vinegar mix.

  5. Dry everything, then put it back

    Let every part air dry for an hour, put the unit back together and run it. The air should smell neutral within a day.

  6. Stop water from sitting

    Tool used: Dehumidifier cleaning tablets

    Empty the bucket daily, or run a hose for continuous drain. Add a cleaning tablet to the bucket as the label says, so slime does not rebuild.

    Dehumidifier cleaning tablets (illustration)
    Illustration

    Tool for this step

    Dehumidifier cleaning tablets · Drop one in the bucket as the label says

    Check price on Amazon

When free fixes aren't enough

If the smell survives a full clean, check the room. Musty air from a damp basement passes through the machine, so the real fix is finding the leak or damp source. Mold growing on walls or other surfaces beyond about 10 square feet is a job for professional help, according to EPA guidance. If you smell burning, hot plastic or an electrical odor, unplug the unit and stop using it. Cleaning tablets earn their place for people who run the machine all season and do not want to scrub every two weeks. A replacement filter is worth it if the filter is stained or brittle.

Buy the fix

Still stuck after the free fixes? These are the products we would look at.

Best pick
Dehumidifier cleaning tablets (illustration)
Illustration

Dehumidifier cleaning tablets

Fixes: slime and mildew growth in the bucket between cleans

Look for: A label that names dehumidifier buckets, tanks or drain pans; Clear dosing for your bucket size; Unscented or a light scent.

Who it's for
Anyone who runs a dehumidifier all season, or who skips the scrub.
Honest downside
Your manual forbids additives in the bucket, or you drain through a hose with no standing water. Check first.
Check price on Amazon

As an Amazon Associate I earn from qualifying purchases. We don't show prices because they change, so use the button to see today's price.

How we picked: How we picked: this page is based on dehumidifier manuals and care guides, EPA mold guidance, and the problems and fixes people report in reviews. We do not test products by hand.

Put it away clean at the end of the season

  • Empty, wash and dry the bucket, filter and housing.
  • Store the unit upright with the bucket out so air can circulate.
  • Cover it loosely with a breathable bag, not sealed plastic.
  • Check the filter and replace it if it is stained or brittle.

What to skip

Bleach and air fresheners

Bleach can damage plastic and metal parts, and mixing it with vinegar makes toxic fumes. Air fresheners hide the smell for an hour and leave the mildew in place. Clean the parts instead.

Frequently asked questions

Why does my dehumidifier smell like mildew?
Water sits in the bucket, and moist air keeps the filter and coils damp. Mildew grows on them and blows into the room. Cleaning all three removes the smell.
Why does my dehumidifier smell bad?
Mildew is the usual cause, but a burning, hot-plastic or electrical smell is different. Unplug the unit and call the maker or a repair shop.
How to stop dehumidifier mold?
Empty the bucket daily or use a drain hose, dry the filter fully, wash the bucket weekly and keep the unit a few inches from walls for airflow. Cleaning tablets in the bucket slow regrowth.
How often should I clean a dehumidifier?
Every two weeks in heavy use, monthly otherwise. Do a deep clean at the start and end of the season.

As an Amazon Associate I earn from qualifying purchases. Affiliate disclosure

Dehumidifier cleaning tablets (illustration)
Illustration

Our pick: Dehumidifier cleaning tablets

Check price