Mine is the el-cheapo version 10x10 ($299 on sale, I think?) without the ridge vents. I just crack a "window" on either side of the tent to vent my buddy heater when I need it. Most nights I turn off the heater but when it dips below 25 or so, I leave it on low all night. When I get up in the morning and turn on the Coleman lantern then the stove to boil water, it gets downright toasty in that tent within 2-3 minutes. Even on the 13 degree morning last week, I was eating breakfast with just a shirt on.
I really like the way that tent handles the wind too. I don't bother using the awning, since I'm too tall for it (that awning is the only thing I've found so far that I don't like about the tent, but it's easy to roll up and forget about too). On a really windy week on the flats in NW Colorado last year, the awning poles fell out enough times that I just rolled it up and forgot about it. As I was leaving Colorado last Saturday afternoon, the winds were cranking about 20-25+ and I saw several small pop-up campers and tents just getting shredded.
Of all the investments I've made for my elk/mule deer camp over the past 5 years, I'd put that KC tent near or at the top.