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Flue Safety

By Tim Krof

A properly installed and functioning flue is essential for home safety. Carbon monoxide and other gases are lighter than air and will float up through a flue without the assistance of a blower. Flues need proper clearance from combustibles and should be properly vented to exterior.

In the process of venting the combustible gases from the furnace or water heater, the metal flue will heat up. These metal flues can be either single wall or double wall in thickness. A single wall flue requires 6” of clearance from combustible materials such as framing materials or drywall. A double wall flue requires only 1” of clearance, due to the decrease in heat created between 2 walls of separated metal. If you have ever accidentally touched a flue from a running furnace or water heater you know just how hot they can get! The heat that is emitted makes improper flue clearance a safety concern due to the potential fire concern.

Newer flues are made from galvanized metal and run directly to the exterior. In older homes that have an original masonry chimney, it is important that the metal pipe from the furnace or water heater is properly sealed at the penetration point. Missing mortar or improper material used for sealing can create safety concerns due to possible leaking of toxic and combustible gases back into the interior dwelling. With some attention to the correct installation and maintenance of flues we can ensure that the devices that keep us warm are venting properly and safely.