The answer to 'why is my humidifier blowing hot air' is that your humidifier is likely not functioning properly and may need repair or replacement. Humidifiers are designed to add moisture to the air, not heat it. If your humidifier is blowing hot air, it could be due to a malfunctioning heating element, thermostat, or other internal component.
Some common causes of a humidifier blowing hot air include a stuck or faulty humidistat, a clogged water line, or mineral buildup in the unit. If the humidifier is old, it may simply be time for a replacement. In some cases, the hot air could also be caused by a problem with your HVAC system, such as a malfunctioning furnace or ductwork issue.