Poor Air Quality

• The first danger that a plugged furnace filter poses is a reduction in the air quality in your home. As warm air circulates through each of the rooms you heat, it collects pollen from indoor plants, dander from pets, household dust and debris from pollution. All of this material collects in the filter, where a buildup can cause it to recirculate and aggravate allergies.
  
  

Fire

• Furnace filters that become plugged with flammable debris, including dust, hair and fibers, pose a threat of fire. Heat from the furnace can ignite material plugging the filter, causing it to burn at a high temperature that may ignite nearby objects or other parts of your home. Even a small furnace filter fire will circulate smoke throughout your home, posing a health danger and requiring a messy cleanup.
  
  

Poor Efficiency

• As a furnace filter becomes more and more plugged, it will reduce the efficiency of your entire heating system. To keep your home warm based on your thermostat settings, the furnace will burn additional fuel. This increases your energy consumption and, in turn, your home heating bill. A clean filter allows the furnace to function at its advertised efficiency settings, keeping your heating bills under control and placing less strain on the furnace.
  
  

Carbon Monoxide

• In extreme cases, a clogged furnace filter can cause the furnace to vent dangerous carbon monoxide fumes into your home. Carbon monoxide is the colorless, odorless byproduct of burning natural gas to produce heat. A furnace that vents carbon monoxide into the home instead of outdoors can cause illness and asphyxiation. A clean filter and a carbon monoxide detector will ensure that the air you breathe indoors is safe.