The answer to 'humidifier smells bad' is that a smelly humidifier is often caused by bacterial growth or mineral buildup. This can happen when the humidifier is not cleaned and maintained properly. Symptoms include a foul, musty odor coming from the unit. The solution is to clean and disinfect the humidifier regularly following the manufacturer's instructions. This usually involves soaking the tank and other components in a vinegar or bleach solution to kill bacteria and remove mineral deposits.
If the smell persists after cleaning, it may indicate a more serious issue like mold growth or a mechanical problem. In those cases, it's best to call a professional HVAC technician to inspect and repair the humidifier.