There are a lot of unknown factors in your question including the size of your room, whether or not you are also using the fan to vent the room, how many angles in the ducting, type of ducting, addition of a carbon scrubber, and on.

It's easy to figure out. Follow the formula here:

http://boards.cannabis.com/indoor-gr...ml#post1634834
bigsby Reviewed by bigsby on . 2 x 1000w HPS Ventilation Question In the process of setting up my new room and just had a quick question. Plan on running 2 air cooled 1000w HPS in a row with one fan. Both hoods will be Magnum XXXL with 8" flanges. Will a 8" Max Fan rated at 667 CFM be enough to cool both of the hoods? The ducting run will be minimal, under 10' total. Plan to use sheet metal ducting for everything. From what I've been reading it should be plenty, but just wanted to get a few more opinions from people running a similar setup before Rating: 5