Outdoor Furnace Ash Removal - Don't Make This FATAL Mistake!

Ash Removal - Don't Make
This FATAL Mistake!

(Ultimate Summer Shutdown Checklist Part 8 of 10)

I visited a customer's home last summer to help him with a modification of his outdoor wood furnace system, and when I opened his firebox to look inside, I found that his firebox was half full of ASH!! PLEASE DO NOT make this fatal mistake!!! Ash will eat through steel! 

The level of ash in an outdoor wood burning boiler should never be deeper than THREE INCHES.


A deep layer of ash causes two main problems:

1. Deep ash reduces efficiency

2. Ash can be highly corrosive and it can eat holes in your firebox steel.


During the summer months, ALL ash should be removed, and the firebox should be completely scraped clean.


EFFICIENCY: The heat from your burning wood transfers into the outdoor wood burner water through the 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 furnace.


It is sometimes funny for us to see poorly maintained 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 (DON'T 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 stove. All wood contains moisture. That moisture should leave the outdoor wood boiler in the form of steam.


However, deep layers of ash can absorb that moisture and form an acidic paste that can eat holes in your furnace firebox. It is NEVER funny for us to see this. 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.

Coming Soon - Part 9! "Filter Kit - Why Needed for ALL Outdoor Boilers"



How do I Clean the Lower Ash Chamber?

  • Use caution. Only open the lower back door when the furnace is switched to the off position. Using the provided cleaning/scraping tool, remove ash from the lower chamber as necessary, at least every week. Always remove ash into a covered, non-combustible container.


Why is water treatment important?

  • The chemical (water treatment) coats the inside of the furnace to reduce the effects of corrosion on the metal.


What do you mean by proper ash management?

  • If the ash becomes wet it is corrosive to the metal of the furnace. If the level of ash is too thick in the water box it does not allow for efficient heat transfer to the water in the water jacket of your outdoor wood burner. The temperature of the water in the jacket is used to heat your house.


May I buy outdoor wood boiler parts directly from OutdoorBoiler.com?

  • YES, of course! To order outdoor wood furnace parts, visit our online store at OutdoorBoiler.com by clicking HERE, or call our office at (231) 861-8200, or (888) Log-Burn.


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One of the most important steps in prolonging the life of your outdoor boiler is to ensure that the water in your boiler is not corroding the steel. Water starts to eat holes in steel immediately upon contact (through rust corrosion) unless properly treated. We test your outdoor boiler water for free! Learn more.