Exhaust Question

I have 4ft x 8ft x 7 ft grow area, and im wondering what size exhaust fan to get. As now with just a T5 its around 85 , and it has gone higher. Any help is appreciated .

Any air you exhaust has to be replaced by something. If the Air you are replacing it with is 95* you will have problems.. If it is 40* you will have problems..

Hopefully you are removing hot air and replacing it with cold air. The difference (split) is where your exhaust fan will come in. The greater the split the less fan you need.

The temp outside the grow is around 70.

hot, cold or indifferent.......you want to exchange your air several times a day. a six inch in-line fan, with a controller, would be my pic. passive intake.

What kind of CFM s would i need?

ohhhhhhhh no. i'm not doing your math.........nice try

how do you calculate it...

does 224 cubic feet to a room that size sound right?

sure......and put it on a controller, for the dark cycle, so it doesn't get too cool, if that is a possibility. avoid big swings

Thanks for the help