Mt Bob
Minister of Fire
HI,don't really know boyle's law,but less pressure at higher alt.,same as high pressure for divers and mine workers.Appliance adapter may still be attached to the back of the Accentra. For our termination cap, we have a "turbo" cap which is conical in shape and has an interior screen that keeps out most critters. You may want to think about a solid cap for when you are not using the stove - especially if your away for periods of time in cold weather. Amazing what people have found that had crawled in the venting!
We have Biovent - has the silicone gasket between sections and only requires 3 screws on joints. A bit more expensive but no hassles to assemble/disassemble. Gaskets are replaceable. http://www.woodmanspartsplus.com/764374/products/Bio-Vent-Wall-Vent-Kit.html?d_id=50465 Not sure if they carry an adapter for Harman...
Too many years living with a commercial diver where the pressure is always increased Is it Boyle's law, pressure and volume inversely related?