well its 8 foot by 4.2 foot across by 1.2 foot
how many cfm u think i would need im geting into atic tomarrow see what kind area i got to work with i was going to do some form of exh fan and add atic fan to drop vent outside with some from carbin fliter on there
Just multiply length x width x height. Almost any fan would have that capacity. Let me tell you about my exhaust. At the time, I could not afford a canfan and carbon filter. I knew it was important, just couldn't afford it. I do have an attic space over my house, so I cut a hole in the ceiling and bought a diffuser, about $10.00 at the big box stores, attached about 20' of 8" duct line, I used the insulated flexible duct, and installed a 8" in-line duct booster I bought at Menards for less than $30.00. Shoved the open end in one of the roof hats, they are there to vent your attic. The 8" DuctBooster is rated at 500cfm, across that length it is probably about 3/5 of that or a convineint 300cfm. My room is 10 x 8 x 14, a little over 1100 cuft. and I want the air exchanged every 3 to 5 minutes.
See, there are not many people walking around sniffing the air at the peak of my roof, so I can use a cheap fan, larger diameter is better, and exhaust it were no one can smell it anyway.
The intake and exhaust do not have as much to do with temperature as some folks think though, whatever the 'ambient' air temperature is will be the temperature of the air you intake. When its 80 degrees out, the air I am in-taking is already 80 degrees, that is before you add the lights. As you have pointed out even floros can change that by as much as 20 degrees. That is why I posted this thread about air cooling the lights.
There are no short cuts, you must have all of the parts of a good air handling system, whether it is a box or a house, seal it up so you have a 'controlled environment', then install the system necessary to keep your controlled environment ideal for what you put in the environment.
The only difference between what your plants need, and what you need is you breath oxygen, and they breath carbon dioxide, and they can't move. If it was 80 degrees or more, with 70% relative humidity and no breeze, would you stay in the room??
VV