Central humidifiers are built right into the heating and air conditioning system. They are designed to humidify the entire house by emitting a fine water vapor. But beware! Humidifiers are very useful but if not properly maintained, they can make you sick.
They can ease dry sinuses, bloody noses, dry skin and other symptoms related to respiratory conditions. If not properly cleaned, dirty humidifiers can breed mold or bacteria. You should always consult with your doctor before installing or using a central humidifier if you have allergies or asthma.
Always follow the manufacturer’s guidelines for setting humidity levels and for cleaning the system properly. Your HVAC professional can also help with proper usage and maintenance. Here are a few tips for maintaining the cleanliness of your humidifier which is so essential to good health:

• Clean the drum and tray once a month. Make sure you shut off the water supply first!
• Check the float assembly for scale. Scale on the float can cause leaks. Clean or replace.
• Check the area around your system for wetness caused by leaks.
• Clean or replace any sponges or filters.
• Always turn off the water supply in the summer and clean and drain the drum and tray. If you
  have air conditioning, there could be a metal knob on the humidifier to block air flow.

Over time, all humidifiers can build up deposits that are very difficult to clean or remove. This can encourage growth of bacteria. Consider replacing older humidifiers.