Flues can be dangerous when clogged with snow, so be sure to keep an eye on them. If you live in a mobile home, keep snow away from the furnace vent on the top of your trailer.
A furnace malfunction can lead to carbon monoxide build-up in your home. And that can cause heart and lung failure, brain damage and death.
If you're experiencing flu-like symptoms, firefighters advise you to check the carbon monoxide levels in your house. They say detectors should be in all homes with gas-operated appliances.
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Steps to Reduce Carbon Monoxide Exposure
Source: http://www.epa.gov/(United States Environmental Protection Agency Web Site)