Retailer saying I need a bigger fan

Check out this video (maybe jump to 16 minute mark - the beads are a cool visual as to why a bigger fan is nice too..) https://youtu.be/JwtkHxv_3pU

Retailer is spot on.

Hello. I would go with the bigger fan. I've got a 8" fan on a 6" line. When I hooked it up the first time it was too strong. I put a dimmer switch (like in some dinning rooms, to dim the lights) Ask about a controller or hook up the dimmer switch. I have it on about 2/3 in the summer and close to off when its freezing out. Good luck. Chuck.

For a tent of that size, an 8' fan and filter would probably be the best bet. The last thing you want to do is have everything set up and then realize your fan isn't powerful enough to extract the stagnant air inside your tent properly. I'd say go with the 8" to be safe and ensure that you won't have any issues with air flow!