Amount of air circulation?

ive got a grow room 120 x 120 x 200 cm with an inducting fan with 250m3/hour specs (5inch)... any ideas how long this should be left on for? as im tryin to offset my electricity spike as much as possible!

im kinda workin it out as i type lol im guessing every 2 hours ( or just under ) it will move the whole of the iar in the tent... but how many times does the whole of the air in the tent need to be "refreshed" as per keepin the spike down id like to work to a minimum as raise specs as per growth results...

any info ie number of hours i should leave it on per day... i have a fan in there to stop it getting "stuffy" aswell, so this could be on when the ext fan isnt. actually this is on permanantly anyway ( direct on plants ) to keep heat stress down. As im having a bit of a test tryin to work out optimum distance of my 250 MH on my plants...

If I remember correctly you want to replace the air every hour. However, the fan is not going to be noticeable in power consumption.

Figure our square feet in the room, and then look at some fans and see what type of power you need to clear out your room.

Someone above said he read clean the air once an hour, I shoot a shit ton higher than that myself. I haven't done the math but I have an inch out and six inch in, and the room really isn't enormous. 7X10 or so

ive read somewhere (think it was jorge cervantes) that your supposed to replace the air of the room 3x every 5 minutes. i personally have a 180ish sq ft closet and i use a 172 cfm fan. i plan on getting another one (for odor control)