Gas Furnace Venting Into Chimney

Taking care of the vent on your gas furnace is extremely important but working improperly and damaging your vent can have catastrophic results.

Gas furnace venting into chimney.

For gas venting appliances the chimney flue venting rules are more complex simply because of the variety of products on the market. A gas stove can be vented through an existing chimney whether it is a manufactured or masonry 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. This structure generally uses the furnace vent pipe through roofbecause the b venting pipe is designed in vertical manner.

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. The vent pipe or flue is a vital component of the furnace that transmits emissions from the combustion process out of the building. The area around the flue piping should be sealed where it enters the chimney. When the furnace exhausts into the chimney the gases quickly cool off before exiting to the outdoors.

To aid in removing the vent pipe a thimble or slip joint may be used. 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. Refer to figure 2. 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.

When the vent is withdrawing air from the house it expels the gas outside through the vent. The vent pipe must be firmly attached and sealed where it enters the chimney in order to prevent it from falling out to prevent air leaks into the chimney reducing the effective draft and to prevent flue gas leaks out of the chimney. When venting two appliances separately into a common chimney always install the smaller flue pipe appliance with lowest gph input at a higher point into the chimney than the larger flue pipe for the appliance with the largest gph input. A conventional natural gas furnace will vent the dangerous combustion gases through a simple vertical exhaust system that is attached to the furnace.

This undermines the entire purpose of venting the furnace in the first place. Also known as the type b this vent is operating on the natural air convection. Furnaces that vent into chimneys can be hazardous but they don t have to be. For many homes a gas furnace is the preferred heating device it has proven to be an efficient and reliable way of meeting household heating needs over the years.

To ensure proper venting however a liner must first be installed in the chimney.