ventilation for closet?

How should i vent 2.5 x 1.6 4ft tall.

Very good idea to vent. If you can vent through your ceiling into the attic, use a 4" hole-saw bit to make the hole, save the disc so you can glue it back in later to cover your tracks. If you can get into the attic, hang it up there and it will be nice and quiet. Fans work better pulling air than pushing air.

thanks for the idea, can u suggest a good fan i was thinking a cpu fan

Computer fans work fine. A 4" case fan moves a little more that 100cfm, which is more than plenty.

For the size of your grow area PC fans would work but.......

Do not assume that fan size has anything to do with CFM's and do not assume that because your fan is rated at 100 CFM's that it is actually going to move that much air from your cabinet. Axial propeller fans are pretty inefficient at moving air under resistance and combined with the fact that its still just a DC powered fan may make you want reconsider using them.

If you have the PC fans already then fine, use them. But if you don't already have them, then I would consider using a bathroom vent fan. It will most likely be quieter and stronger. I have a Delta that is rated at 134 CFM's in one box and in another box that is a little larger I have an 80 CFM bathroom fan that kicks the Deltas ass all day long.

If you decide to use PC fans then use one as an intake and another as an exhaust.

Good luck.

thank u both for your ideas, i haven't bought any fans yet but i think two 100mm cpu fans should work because with the fan i already have "off" the cabinet gets as hot as 95 degeres another question i had was, Is mylar needed at the top and bottom of the cabinet?

mylar will work but will increase your temps and its a pain in the arse, flat white paint will work fine.