Thanks for the reply....
If I use CO2 then no need to vent the room?
Its a bedroom...Any need to vent it if the heat is controlled?
There are 3 parts to the air handling system for your grow room, one you mentioned, air cooling for the lights. It would be possible to vent all 3 of the ones you mention with one system if it doesn't have to many bends in it. It would be better to pull air from lower and exhaust it higher, do not just dump it in the attic, vent ot to the outside , it will be more efficient.
The second part of your air handling system is your intake ane exhaust. The reason is your plants are going to need 'fresh air'. Our air does contain CO2, not enough for a room full of CO2 eating monster plants, so every 3-5 minutes you need to replace the 'stale' CO2 depleted air with ' fresh air'. You would size your exhaust fan based on the cubic feet of the room, if you have 8' ceilings you have about 800 cuft. Keep in mind that the fans rating is based on not haviong any flow restrictions, no bends, no 'T's, they are flow restrictors, and if you intend to use carbon filtering oversize your fan, get the good one for that system, usually a CanFan. Your intake can be passive unless smell is a concern. If you do use a carboin filter, you will need an intake fan slighly smaller than the exhaust fans capacity, creating a slight negative pressure.
The third part is the easy part, an ocsillating fan or two to keep the air moving around, keep the air under the canopy 'fresh', and strengthens the plants stems.
What you need to do is put yourself in the place of your plants. If you are baking in the hot sun, with no breeze........and you have an attic to work with....no excuses, do it right. VV