Wow, I figured out how to disable email notifications this morning....every bit of gibberish posted here landed in my inbox this morning lol...!
Anyway, SBI got back to me....Claiming that every front end failure of the tundra was related to either over drafting or inadequate air through the unit. They see no reason that I shouldn't put my serial 1906 into service, and that the redesign was done in order to make the unit more resiliant to poor installation (operation?) conditions. In other words, the failures were our fault, not theirs, and they won't consider replacing my unit until it fails..
My response: (indentities concealed to, well, conceal identity)
Dear XX,
Thank you for your prompt reply. I fully understand that SBI is unable to control every aspect of installation or operation of their products once in the hands of the final user. Failures of any machine indicate how that product accepts its operating conditions within the limits of it's mechanical design. I fully intend to install and operate my furnace within the limits of that design, for reasons of safety and longevity. I selected the Tundra furnace based upon the reviews it gained online, as it is clearly an efficient, effective and easy to use design. Excellent customer service is also another factor.
As the heating system in my home is, with exception of the chimney, being designed from scratch, I have decided to hire a qualified HVAC contractor to design, test, and record the actual performance of the system, so as that it will meet the requirements of the furnace. I will also submit the design and measurements to you in order to ensure I am not overstressing the unit. My plan is to operate well within guidelines, essentially "babying" the furnace. I'd like to see maximum longevity from the furnace, and I refuse to comprmise on safety. It will be set up correctly.
I myself, am a journeyman machinist with a rather extensive welding background. Understanding stresses and thermal expansion of materials is a key component of my trade. This being said, with a basic understanding of the stoves function, the interaction of thermal stress between the front plate of the furnace, the heat exchanger, and the firebox does concern me. When the heat exchanger and the firebox are heated at different rates, thermal expansion of the components will be different. As a result, the two components are fighting each other through the front plate of the furnace. As the front plate is loaded in shear (and likely torsion at points) this proves to be the weak link where failure occurs. Even when operating under ideal circumstances, there is the possibility of several loading events during a normal burn cycle ie: during secondary burn, heat exchanger tubes are hottest, thus pressing forward at the top of the front of the stove. As the wood degasses, coal burn takes over, placing the majority of the heat in the firebox itself. The heat exchanger contracts, the firebox expands, and reverses the bending force on the front of the stove. This repeated stress may be causing failure, even without a discrete over-temperature event.
This theory is borne out in online reports that your updated model has free-floated the heat exchanger body from the front wall of the furnace.
You have assured me that the original design of the stove will survive normal usage under ideal installation situations. Again, I will satisfy the requirements set out in the manual, and have professional record to verify. In the event of failure of the unit, please assure me that the warranty will apply and that an updated unit or repair options will be available.
Best regards,
mcmac