It’s starting to look like the diesel heaters have a maximum exhaust pipe length somewhere between 5 and 10 feet. They seem to be doing fine now with good air filters after cleaning and running without the exhaust extensions and WMO for a couple weeks. I’ll get back to the WMO at some point if they stay good until spring like this. We’ll call this the (O)perational (A)cceptace (T)est phase.
Overall tho, I cannot recommend these things. The Chinese build quality is just horrible, resulting in numerous pitfalls. They can be installed and run safely and reliably by a competent handyman. But the potential safety issues overrule this system for most people, IMHO.
The are a few different ways these things can kill you with carbon monoxide, fuel leaks and resultant asphyxiation and fire. The worst problem I found was a loose plug in the injector chamber. Don’t know where it went or exactly when it fell out, probably the 1st time I cleaned it. You could easily have a fire on your hands if that let go running.
Under the best conditions, like other portable heaters or anything of this nature, they should never be run un-attended. Long-term longevity seems doable, being the simple device it is. Fan and pump are the only moving parts. If you can get them setup and running right and follow some simple safety precautions, they should be good. That setup part is going to be a challenge for many people – it was, for me.