what is the death of an OWB?

warno said:

There is steel in contact with water in each type. So on the corrosion topic alone is a gasifier be there than a standard owb? I know the gasifiers are much more efficient but I'm just wondering about keeping corrosion to a minimum. Will a standard unit rot out faster then a gasifier?

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Typically gasifiers are closed and pressurized, so no oxygen can enter the system if the system stays sealed. Once the oxygen in the fill water is used up by converting some iron to iron oxides, there is no more corrosion. If water leaks out continuously and is being replaced by makeup water, then that's another story, but easily avoided. (The system fill water needs to have proper pH and so forth.)

Typically OWBs are not closed and pressurized, and require water chemistry management, which can be done and can be done well, but it's not as easy-peasy as a closed and pressurized gasifier. So OWBs won't necessarily rot out faster on the water side if water chemistry is maintained properly. (And they won't necessarily rot out faster from the fire side if operated correctly with dry wood, return temperature protection, and a clean dry off-season firebox.)

But there are a couple non-pressurized gasifiers that are not closed and pressurized, most notably Garns and the P&M gasifiers, which are therefore gasifiers that require water chemistry management.

And I believe Hardy OWBs are sealed with an atmospheric pressure bladder type expansion device, so they might qualify as a closed OWB that would require less water chemistry management.

Also consider the installed cost of an owb vs indoor. That 1 1/4 pex, trenching, hx, and spray foam is pretty expensive. I picked up my biomass used. I replaced the nozzle and refractory and it's pretty much new again

davem3261 said:

Also consider the installed cost of an owb vs indoor. That 1 1/4 pex, trenching, hx, and spray foam is pretty expensive. I picked up my biomass used. I replaced the nozzle and refractory and it's pretty much new again

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To me it was priceless to get it out of the house. Best decision I ever made was to put my biomass in a shed outside the house. No mess, no worries about a house fire, etc, etc, etc...

I have to agree, the heat lost due to having it outside is worth the sacrifice for the other advantages., I'd do it again also. Best to put storage inside if you have the room though.

Having owned an OWB for more than 24 years I have some experience with this. I have also done some research. I will answer the second question first:
What is the number one killer of the boiler itself? Burning garbage is a good way to ruin the firebox quickly. Plastic and rubber when burned with wood will create chloride and sulfurous gases and when mixed with moisture from the wood combustion results in sulfuric and hydrochloric acid! This will result in catastrophic corrosion failure normally worse above the ash line. Maintenance of the firebox while operating is important. Leaving ashes packed and undisturbed in the bottom will result in moisture trapped beneath the ash and corrosion will occur below the ash line. Large dry, chunky combustion byproduct deposits on the inside surfaces allowed to remain for long periods of time will result in corrosion under the deposits. Next filling the water jacket with water whether it is a pressurized system or not without using a good corrosion inhibitor is certain to immediately start the corrosion cycle in the water jacket. This effects every part of the firebox and water jacket and if left untreated will result in corrosion failures that are not reasonable to repair economically. Ferritic stainless, 400 series, 409 etc, corrode quite well with most water conditions if not inhibited. Some of the austenitic stainless, 300 series, 304 etc will take very little chloride in the water supply to cause failures.

Now, how to make them last a long time.

Burn only untreated wood! Use a heavy rod or poker to loosen the ash bed every day or two when refueling, paying attention to corners. Scrape any large dry chunks off the walls and inside corners every few days with a metal hoe. I have never seen corrosion caused by the shiny creosote on the walls. Always be sure to use the manufacturers water conditioner/inhibitor and be sure to maintain to the correct level. If you have a leak in your system from fittings be sure to repair the leak so you don't frequently add water diluting the inhibitor. Carefully inspect the inside of the firebox each year after the heating season to identify whether or not you have been neglecting any areas that can be showing corrosion as a result. This is all very simple maintenance and it can save your furnace from certain failure if you choose not to maintain properly.

My first furnace where I now live was 12 years old before I traded up to an EPA Phase 2 furnace. The inside of that 16 year old furnace was almost perfect condition because I took care of it well. My first furnace I owned at my previous home was not quite so nice inside because I had not understood the importance of those few maintenance needs.

Carbon Steel or Stainless 400 series need the same maintenance attention and both will last as long as you choose to maintain properly. My father experimented with numerous stainless projects in his hobby involving steam engines. He was surprised how stainless can corrode under numerous conditions. All the steam engines he fired were many many years old and they were carbon steel.

Always burn seasoned wood. It does not remove the importance of maintaining correctly but it will burn cleaner and much more efficiently than green or unseasoned wood. A cord of seasoned oak contains about 160 less gallons water than a cord of unseasoned oak. Not very hard to understand the importance of using seasoned wood.

I hope this information and sharing of my experience helps.