The direction of connector pipe installation for solid fuel-burning appliances can be crucial for ensuring safe and efficient operation. Common industry practice is to install the connector pipe with the male (crimped) end pointing downward toward the appliance. This orientation allows any creosote or condensate to flow back into the appliance, reducing the risk of leaks at the joints and minimizing the potential for creosote buildup, which can lead to chimney fires.
What Do the Codes Say?
NFPA 211
The NFPA 211 does not specifically prescribe the orientation of connector pipes, though it talks a lot about proper installation and decrement of sections.
IRC
The IRC states:
“M1803.3 Installation. Vent and chimney connectors shall be installed in accordance with the manufacturer’s instructions and within the space where the appliance is located.”
It does not specifically prescribe the orientation of connector pipes.
However, we also find:
“M1801.3.2 Flue passageways. The flue gas passageway shall be free of obstructions and combustible deposits and shall be cleaned if previously used for venting a solid or liquid fuel-burning appliance or fireplace. The flue liner, chimney inner wall, or vent inner wall shall be continuous and free of cracks, gaps, perforations, or other damage or deterioration that would allow the escape of combustion products, including gases, moisture, and creosote.”
The Risks of Improper Installation
In this case, a connector pipe installed upside down would allow the escape of combustion byproducts during sweeping, and during a chimney fire, potentially creosote as well. Creosote could also flow down the outside of the pipe during normal use, without a chimney fire, because as creosote heats up it can flow down the inside of the chimney slowly and re-harden when heat is removed. If sufficient heat is not present to ignite it but to allow it to flow, this is a real possibility and one I have seen many times, where creosote has hardened in flowing lines on the outside of the connector pipe.
What Do Manufacturers Recommend?
Manufacturers of both connector piping and manufacturers of solid-fuel appliances may also specify the orientation of their pipes. On connector piping, there is often a sticker on the pipe (if included) showing an arrow pointing in the direction of exhaust flow that will indicate that the male end of the piping points downward and the female side upward. Nearly all single or double wall piping, as well as all Class A piping that I know of for natural draft solid-fuel appliances, are manufactured with the male end pointing downward toward the appliance. To properly connect single and double wall piping to chimneys at the ceiling or wall would require installing them with the seams in the proper direction. Otherwise, the connection would be backwards as well.
How We Document This in Our Reports
CONNECTOR PIPING INSTALLED UPSIDE DOWN: Connector piping must be installed with the male pipe ends pointing down. This aligns the pipe seams in such a way as to prevent migration of soot and creosote out of the pipe. During the inspection, it was noted that the connector pipe was installed partially or completely with male pipe sections pointed up instead of down. As such, the seams are inverted and every time the chimney is swept, materials such as soot and hardened creosote inside the pipe can migrate to the outside of the pipe. Additionally, in the event of a chimney fire, flaming liquid creosote—which flows down the inside of the pipe—upon reaching these reversed seams, can exit the flue and enter the home. This is a fire hazard and may result in soot entering the home, overheating and ignition of nearby combustibles, or the entry of open flame from the flue into the home. This and all other deficiencies should be properly resolved prior to continued use of the system.
