1. Carbon monoxide poisoning

If your furnace or a gas appliance malfunctions, your house could fill with odorless, colorless, carbon monoxide gas that can be fatal. The Centers for Disease Control estimates that carbon monoxide poisoning kills over 400 people annually.

Prevent it

  • Install $40 carbon monoxide detectors near the furnace and your bedrooms. Buy one recommended by Consumer Reports or one with an Underwriters Laboratory “UL” mark that also says “Single Station Carbon Monoxide Alarm” and has an audible alarm.
  • Get your HVAC and gas appliances serviced every year. Leaking natural gas can cause your house to explode.
  • Don’t run cars in the garage with the garage door shut — more people die from carbon monoxide poisoning from idling cars than from furnaces, the CDC says.