while 81 or 83 is perfectly fine would be starting to attempt to do something when temps got up to around 85 to keep them from going any higher and while plants may still grow at 90 degrees they do not do not grow their best at that temperature.
there is no reason to use a closed circuit unless you are using co2 in wich case you would probably need a/c to keep the room cool in the summer.
in an open system you just need a good sized intake that will pull cool air into the room and if the one in the floor is your coolest source of air that should be your intake to pull cool air into the grow room if you can make it large enough for an intake you shouldnt need any other blower or fan if you are restricted in size to just a 6 or 8 inch hole you will probably need a blower or fan to pull enough air in to make a difference.
bejay Reviewed by bejay on . Question about intake? Got a few cycles under my belt, but I am for the first time running into some temperature problems. Right now it's 81 in the room, trying to keep things down. As of now I only have an open circuit that is taking warm air out of the room, through the lights, and into the attic via my Vortex fan. There is also a hole in the floor that would be perfect for pulling cold air in... is this the passive intake? In a nut shell I am proposing that I attach some ducting to the whole in the floor Rating: 5