When heat is able to escape from an outdoor wood boiler through a leak in its combustion chamber, or fuel-burning container, the end result is lower efficiency: the boiler must burn more wood to produce the heat your home requires. While outdoor wood boilers typically have efficiency ratings in the 60- or 70-percent range when burning cord wood, this efficiency rating can drop significantly as a result of heat leaks. One of the major culprits of heat leaking from an outdoor wood boiler is a poorly insulated combustion chamber door.
Creosote is a dark brown, foul-smelling oil that can form when the gases from burning wood condense inside a wood boiler’s combustion chamber. As with heat leaks, creosote leaks are often attributed to problems with combustion chamber doors. However, instead of resulting from poor door insulation, the leaks typically result from a door not being airtight. Outdoor wood boilers that leak creosote are dangerous, because creosote is highly combustible.
Water leaks in outdoor wood boilers tend to form as a result of structural issues with the actual boiler unit, the container that holds water for heating. Most boilers consist of metals such as steel or stainless steel, which are entirely waterproof, but which over time can succumb to corrosion and develop cracks. The welded seams on a boiler are particularly susceptible to leaks. An outdoor wood boiler may also leak water from the transfer pipes that are connected to the boiler unit.
Preventing and Repairing Leaks
One remedy for a boiler that is leaking heat is to replace the existing combustion chamber door with a door that offers superior insulation, such as a water-jacked door, a thick cast iron door, or a water-cooled door; the water-cooled door is the most efficient. For best results, always choose combustion chamber doors that have at least four inches of exterior insulation. To prevent or repair creosote leaks, cover the combustion chamber’s door gasket with a silicone seal. For preventing water leaks, you can mix antifreeze into the boiler’s water to inhibit rust and help prevent corrosion. However, the antifreeze will also make the boiler less efficient. To remedy existing leaks, weld a metal plate over the hole or crack. When faced with a leaking pipe, trace the leak back to its source, turn off the water supply, drain the boiler and repair the piping connection where the leak originates.