Can a Coal Furnace & Propane Furnace Be Vented in the Same Chimney?

Problems

• Propane exhaust contains unburned methane that can ignite if it encounters a spark. If a coal furnace is vented into the same flue as a propane furnace, the methane from the propane exhaust could explode when it meets a spark emitted by the coal furnace. The only way to vent both furnaces into the same chimney is to install separate stainless steel chimney liners, one for each furnace.

Propane Venting

• The exhaust from a propane furnace has a lower temperature than a coal furnace exhaust, so clay-lined chimneys can’t be used with them unless an insulated liner material is installed. Although gas furnaces don’t produce visible soot, they do deposit acidic substances in the chimney that eventually cause corrosion. A certified chimneysweep must inspect a propane furnace chimney every year and clean it if necessary.

Coal Venting

• Coal furnaces can be hooked up to masonry chimney as long as the chimney is lined. They can also be vented to Type HT all-fuel factory chimneys specifically designed for airtight stoves. Ensure that any pipes you use can be used with a coal furnace. Emissions from coal furnaces include sulfur compounds that can corrode the chimney, so your chimney must be inspected by a certified chimneysweep every year and cleaned if needed.

Shared Flues

• A flue is a sealed pathway for venting the gases and particles released during combustion. It can be made out of metal flue pipe or clay flue tiles. Single chimneys can contain more than one flue as long as there’s enough spacing and sealant between them. However, when two furnaces share a single chimney, there is an increased risk of fire or carbon monoxide poisoning unless each furnace has a dedicated flue with a flue divider. Some jurisdictions don’t allow furnaces to share a flue. Check with your local building inspector to see if shared flues are allowed in your community before you install one.