The answer to 'why is my humidifier blowing cold air' is that your humidifier may be malfunctioning or not working properly. This can happen if the humidifier is set to the wrong temperature setting, if there is a problem with the heating element, or if the humidifier is not properly maintained.
Some common causes of a humidifier blowing cold air include a faulty thermostat, clogged filters, mineral buildup, or issues with the water supply. In some cases, the humidifier may simply be too old and in need of replacement. If you've checked these basic troubleshooting steps and the problem persists, it's best to call in a professional HVAC technician to diagnose and repair the issue.