I haven't actually measured on mine (it isn't super sealed), and It just allows the heated bed to warm that air. If I had to guess, it's probable bout 85-90 in there, but I only run the bed at 90 (not the 100 some use). I'll do a quick google run and see what I see.how warm do you want the enclosure to be?
v/r
James
edit to add: quick bit of research says passive heating (bed only) will bring the enclosure temp to ball park of 35-40 C (not far off my 85-90 F guess on mine). Serious optimizing seems to call for active heating, with ABS looking for around 60 to 80 C. But that brings in serious increase in design effort, and draft elimination.
simple version from my perspective; passive heating made a marked improvement in my ABS prints, but more gains can be made with more effort. YMMV.