Carbon Monoxide is the silent killer - its colourless, odourless, and tasteless. When fossil fuels like natural gas, fuel oil, propane, kerosene, wood, or charcoal are burned in appliances such as water heaters, furnaces, stoves and space heaters that are used improperly or in a state of disrepair, CO levels can become dangerous or even deadly. The IBC says that 88% of all homes have something that creates a CO threat. With the heating season now upon us, homeowners should ensure their service technicians check CO levels with every servicing of their fuel-burning appliances, which is recommended at least once a year, and should place mandatory CO detectors near fuel-burning appliances. CO poisoning symptoms to watch for include: headache, dizziness, shortness of breath, fatigue, and nausea.