As Smokey alluded to, maybe the heat is going up (is that a bad thing?). In the past when I have run stoves in the basement it takes a little time to warm things up. Concrete floors etc. I do like my 6041 but it took me a bit of tinkering to get it to run to my satisfaction. Setting #1 is not going to roast you out anyway. I like the way mine burns on #3. I seldom have run it on #4. At #1 you more than likely won't get more than 9000 or 10,000 btu's maybe a tad more, which isn't that much. Once you feel safe enough running it maybe you can bump it up a bit when you are there to watch it. There are a few things that I learned about this stove, it needs a little tinkering but once I got the hang of it the damned thing will burn anything but rocks and it is possible to get great heat out of it. After all that being said, if the 12' horizontal run is hindering air flow you wont get the heat out that you want. It has to breath out before it can breath in.