Gas Furnace Venting Into Chimney

Gas and oil appliance venting.

Gas furnace venting into chimney. The exhaust system typically uses metal venting often routed into a chimney stack to exhaust the combustion gases created in the furnace fire chamber. A chimney is an architectural ventilation structure made of masonry clay or metal that isolates hot toxic exhaust gases or smoke produced by a boiler stove furnace incinerator or fireplace from human living areas. The different types of venting. For instance a 100 000 btu furnace venting into an interior chimney with a 38 square inch liner would not be allowed regardless of chimney height.

I ve never seen one that recent not being lined up to the top so it got me thinking. When did it become dis allowed to vent a furance and or water heater directly into a chimney or is it ever totally dis allowed. There are a few rules to mention. But many don t realize that a gas heating appliance whether it is a furnace boiler or even a water heater relies on the chimney for proper venting of the exhaust.

A conventional natural gas furnace will vent the dangerous combustion gases through a simple vertical exhaust system that is attached to the furnace. Chimneys are usually vertical or as near as possible to vertical to ensure that the gases flow smoothly drawing air into the combustion in what is known as the stack or. To ensure proper venting however a liner must first be installed in the chimney. Well making sure that you choose the right venting style will protect them.

The rules apply to listed appliances. For gas venting appliances the chimney flue venting rules are more complex simply because of the variety of products on the market. The height of the chimney the area of the liner and the input of the appliance all play a role in the use of the chimney. However using an interior chimney is extremely limited.

The manufacturer s listing and instructions will preclude attaching any other appliances to it. A gas stove can be vented through an existing chimney whether it is a manufactured or masonry chimney. Multiple gas or oil furnaces or boilers as well as hot water heaters can be vented into one flue. This chimney rule can be applied to wood burning fireplaces heating stoves and any oil fueled appliances but remember that manufacturer requirements have to be incorporated into it.

I ran across a permitted 2003 installation today of an 80 furance water heater venting into a clay lined masonry chimney. Furnaces that vent into chimneys can be hazardous but they don t have to be. When the furnace exhausts into the chimney the gases quickly cool off before exiting to the outdoors. They can t all rise to the top of the chimney so some of them backdraft through the vent pipe itself and enter the home s crawlspace.