Does the Harman put out a low even heat throughout the whole burn with a full load or does it seem to release most of it's heat at the beginning of the burn cycle? This is what impressed me most from the Blaze King, it can throttle down and keep the outgassing to a minimum during the first part of the burn and seems to stretch it out over a good 20+ hours. So far it looks like the t-stat keeps things under control no matter what the draft conditions may be. The flexibility of reloading anywhere from 12 to 30 hours is also such a nice thing to have when your a 24/7 burner.
The TL300 has an extremely even burn time. While cat stoves do too, if you compare a graph of cat stoves to the TL300, the line is more even with the Harman (slightly higher at the beginnging and lower at the end of the burn for cat stoves). You can check out what I mean here: hearthnhome.com/downloads/brochures/
TL300.pdf
I'm the one that had an open tee in the chimney. We had an old Baker coal stove and decided we wanted to stop burning coal and go with wood. We bought the TL300 mainly because we are in a situation where we have to load it up in the morning and then are gone all day (so needed something with long burn times). Burn times of 12-16 hours are common with this stove (it depends a lot on the type/size of wood).
We had it installed and the company we bought it from never bothered to make sure our chimney was ok for a downdraft stove. We couldn't get that darn thing to heat even our family room, let alone the entire house. We had the company out to check the draft in the stove, check the moisture on the wood, etc. (BTW, Harman told us if the wood is too dry, the stove does not work as well.) The dealer just left us hanging.
It was only because of this forum that we figured out what the problem was. The company that had installed our new chimney for the coal stove left the entire system open -- no cap on the bottom and not joined properly where the pipe from the house met the chimney. We had a new liner put in and what a difference! The stove worked exactly the way the dealer and company said it should. It does take a nice bed of coals (we can usually go from cold start to secondary burn in about an hour) to run properly. But once that is established, you just pop the top open (the top load is awesome BTW), load it up, let things char for about 5-10 minutes, and close the damper. It hums along with a stove top temp of about 350 degrees and pumps out a whole lot of heat.
We had our chimney cleaned this past May after a year+ and there was nothing there. The sweep said whatever we were doing to keep doing it as things were super clean.
The low emissions, huge ash pan (we can get by dumping every two weeks), and long burn times (I have heard people say they've had hot coals after 24 hours) were the reason we chose the TL 300. The fact that it's easy to load, holds a lot of wood, and leaves us with a much larger wood pile at the end of the season are added bonuses.