The level of ash in the outdoor wood furnace should never be deeper than THREE INCHES.
A deep layer of ash causes two main problems:
- Deep ash reduces the efficiency of your outdoor wood boiler.
- Ash can be highly corrosive and it can eat holes in your outdoor wood boiler’s firebox steel.
During the summer months, ALL ash should be removed, and the firebox of your outdoor wood boiler should be completely scraped clean.
EFFICIENCY: The heat from your burning wood transfers into the outdoor wood furnace water through the outdoor wood furnace walls. If the level of ash is too thick in the firebox, it does not allow for efficient heat transfer to the water in the water jacket of the outdoor wood furnace.
It is sometimes funny for us to see poorly maintained outdoor wood furnaces with more than 18 inches of deep ash! You could put your hand into the deep ash and feel the cool ash because it is so deep (do NOT do this!). And a significant portion of the firebox steel is buried in ash so that a large portion of the steel surface area is covered and unavailable to transfer heat.
CAUSTIC PASTE: If the ash becomes wet it is corrosive to the metal of the outdoor wood furnace. All wood contains moisture. That moisture should leave the outdoor wood furnace in the form of steam.However, deep layers of ash can absorb that moisture and form a CAUSTIC paste that can eat holes in your outdoor wood furnace firebox. It is NEVER good to have deep ash, no matter what you have been told in the past. But if you keep the ash layer less than three inches, the ash remains dry and powder-like. Ash is harmless in its powdery state.