If you put a shield on the stove back like a Grandma III you will have hotter intake air. Shield the bottom with opening in front, under ash fender, and up the back, open at top. (shown in VI manual) Your intake won't mix as much cooler room air.
Another way I've toyed with is a double baffle plate, (1/2 inch apart) hollow inside with air holes drilled in rows through the bottom plate. The entire baffle is a preheat chamber. (the hottest part of the stove) Pipe flanges on the top plate with 3/4 pipe going up the stack about 2 feet and out the side of pipe preheats it very well without drilling holes or modifying the stove itself. (the more intake pipes, the more surface heating area, and the slower the flow and longer duration time heating air in pipes. You can also add a twisted steel spiral inside the intake pipe to rotate air against inner pipe walls and increase "dwell time" to increase air temperature - corkscrew fashion)
I didn't comment last year when you started this thread since I never operated a factory built secondary stove to compare my results. I thought mine was poor until the experience I had last winter with a neighbors new Lopi.
Yes, it burned cleaner and less wood. With less heat over an 8 hour duration. For me that = cold house. As my only heat source, I don't have time to babysit it to keep the secondaries burning. I need to load and have 8 hour cycles hot enough to keep the house between 68 and 72. Could be I didn't play with it enough, but as my only heat, and being away 4 to 6 hours, I'd rather burn more wood and come home to a warm house. Plus it makes it more of a space heater with no cooking ability. (the stove was a Mama Bear in the middle of kitchen and convenient to save propane from using range)
Since then we went to the large Kitchen Queen with so much mass and water heating capability we have a very steady house temp. Plus it adds an oven always ready to go. This time of year we wait for the inside temp to drop to about 66 before starting it for night burns. We wake up to about 70* and my 24 hour recording thermometer (in bedroom away from stove) shows a high of 72 overnight. As it gets colder and we burn 24/7 we can keep it within a couple degrees night and day. (I did add a thermostat to the firebox) Adding secondaries to what I've got would certainly ruin the cooktop ability and cause us to use premium wood - take more frequent loading, and end up with more temperature spikes. I guess I'm not a secondary burn kind of guy.
At my second house, my neighbor bought a new Lopi last year much larger than the log home requires. He claims he has the stove figured out, but is adding some electric heat this year. They were cold when it was frigid last winter. I checked it out, secondaries light easily for a couple hours, and it cools with coals until there is room for reloading. Same cycle I experienced with the retrofit Fisher. So I don't think it was me. This is across the street from my log cabin identical to his brought from Finland in kit form in 1972. I put in the same Mama Bear I fitted with the same type Smoke Shelf Baffle as supplied with the later double door stoves (with half the chimney as his) and I don't have electric there for any back up. The reason I didn't go with a Baby Bear for the less than 1000 s.f. area is mine isn't lived in, so it's cold when I get there. Plus it gives me a larger cook top than Baby since it's also my only cook stove and water heater there. I have no use for secondary burn tubes there either.
No kidding!
