The answer to 'why is my dehumidifier smells bad' is that a smelly dehumidifier is often caused by mold or bacteria growth inside the unit. This can happen if the dehumidifier is not cleaned regularly or if moisture gets trapped in the tank or coils. The musty odor is a sign that the dehumidifier needs to be cleaned and maintained properly.
Some common causes of a smelly dehumidifier include not emptying the water tank often enough, allowing water to sit stagnant, and not cleaning the air filter or coils on a regular basis. Over time, this can lead to the growth of mold and bacteria that produce unpleasant odors.