I work in a foundry, and this is what I’ve experienced. During a heat wave the building is hot the first day, hotter the second day regardless of difference in temp, then hotter the next day. It then levels out pretty much, because the extreme heat is fighting to change not the air temp, but the building materials temp, in this case concrete and steel. It takes longer for the materials to heat than the air but once it starts going, the building materials continue to warm, because they also cool slower. Then even at night, it doesn’t really cool off because it takes a long time for concrete and steel to release heat. Honestly the furnaces don’t make much of a difference unless you’re right up on them.