The answer to 'dehumidifier smells bad' is that a smelly dehumidifier is often caused by mold or bacterial growth inside the unit. This can happen if the dehumidifier is not cleaned regularly or if it's used in a very humid environment. The smell is usually a sign that the dehumidifier needs to be cleaned and disinfected.
Some common causes of a smelly dehumidifier include letting the water tank overflow, not changing the air filter, and storing the unit in a damp basement or crawl space. The solution is to unplug the dehumidifier, empty the tank, and clean the interior surfaces with a mild bleach solution or vinegar. You may also need to replace the air filter if it's dirty or clogged. If the smell persists after cleaning, it's best to call a professional HVAC technician to inspect the unit.