These are supposed to be the cheapest/quietest/best exhaust fans to get when it comes to keeping noise down so this is what I've decided to go with.

HVACQuick - S&P TD Series Inline Fans

Now all I need to know is which size fan should I go with for a DR60 tent having a 400wHPS inside of it?

I also haven't picked out a filter yet either so suggesting that as well would be appreciated. Thanks to all who help!

I know that the tent can reach up to 120*F with the 400w light running. Intense

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I think you are gonna need pretty good airflow with a 400w hps in a 60x60cm tent.

My area is about 120x110cm and I have a 600. I started without a air cooled hood, but the temps were way over 95f.

I got the vented hood and now use a 4" vortex (177cfm). This fan isnt really quiet, but it sucks out a lot of heat.

I'm not sure about those s&p fans, I researched vortex, canfan, and elicient (sp?).

I chose vortex cuz its made in canada and has a 10 year warranty.

decided to sell the 400w since it made temps rise way to much in such a small space. going to give the 250w a shot now

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I would have stayed with the 400w.
it cost a bit more to get setup correctly for that size of a tent, but well worth it if you want to cover the whole area with a respectable amount of light. Not to bash on 250W, but you won't get the same exact results or quantity that you would with the 400w.

you could have kept the 400 and given yourself a few more weeks to get the proper fan, since i assume you had to do the same with the 250. This would have allowed you to swap out the 250 w/ the 400 during flowering to really give them a boost.