There always been a bug on heat ventilation, try by yourself : do a flame sweep (costs 15), wait, sometimes the heat will go like 15 ; 11 ; 6 ; 1 ; 0 instead of 15 ; 10 ; 5 ; 0.
Seems like they changed how alacrity works in 4.0 as before 4.0 1.58% alac were enough to fix that, that's not the case anymore.