Space heaters are designed to keep a small area warm and are much more affordable than keeping the furnace on during the night. However, leaving your space heater on increases the carbon monoxide levels in a room, raising a person’s risk of asphyxia. Space heaters are responsible for 79 percent of fatal home heating fires. You need proper ventilation in your room when sleeping with a space heater on to prevent it from overheating, as well, and igniting nearby furniture or clothing. If you want to heat your room at night, it’s best to leave it on while you’re awake and then shut it off when you sleep.