Well, luckily I live in the Scandinavia so outside temps are currently 5-10°c and my flat is at the second floor so it's easy to keep a window open for a while whenever. I don't need to keep it open much if any albeit when these girls are on late bloom in june, temps will probably raise a degree or two. And then it won't be useful to keep the window open since this building is made of fat stone/concrete at the 60's, also my flat is in the middle and facing sunset so basically no heat reflecting towards it. Stays really cool. A little small, can fit only 3x3 and a 2.5x2.5. But hey, things could be worse...easy appartment to grow with 450W. The rent is a bargain...