Reddit mentions of Hurricane Inline Centrifugal Fan, High Performance, Commercial-Grade for Ventilation, 745 CFM - ETL Listed, 8-Inch, Black

Based off of the quantity you have, IF you pipe them all together I would do at least an 8in for main ducting. You could connect 4” or even 6” to the main 8” or larger and then supplement the airflow with an in-line air duct fan. For ~$100 u can get an in-line fan that does 745CFM on an 8” duct. IF you are not connecting them all together and they are each separately exhausting, a 6in will be the minimum IMO.

Hurricane Inline Fan - 8 Inch | 745 CFM | High Performance, Commercial Grade Inline Fans, Quiet Operation - Ventilation Fan - ETL Listed https://www.amazon.com/dp/B006Z1JLN0/ref=cm_sw_r_cp_api_GC7QAbPKKCK20

up to a good start...

If you dont use a carbon filter and you dont have a long run for the exhaust maybe this could be helpfull.

I used a 6'' vivosun inline booster fan for my 5x5 with a 400w hps and it sucked the air out quite fast, a bit noisy should be more than enough for any hps and was pretty cheap compare to the usual inline fan.

and you can buy a speed controller for cheap on amazon too because its almost pulling too much...

https://www.amazon.ca/VIVOSUN-Inline-Booster-Noise-Grounded/dp/B01C82SZRM/ref=pd_lpo_vtph_86_bs_t_1?_encoding=UTF8&refRID=93CSGQER4PC5V7Q26864&th=1

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but if you plan on running long tubing for the exhaust or have 2 or 3 lights together get a bigger inline fan

https://www.amazon.com/Hurricane-Inline-Fan-Performance-Ventilation/dp/B006Z1JLN0

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have an 8 inch (around 800cfm) for a 5 x 10 and with the filter and long ducting run and its borderline. If you have straight and short ducting... you can get away with a smaller fan . The filter will reduce the pull of the fan .

You need to do some math to figure out the temperate that all those watts would be giving off.

Once you have that temperature, you then are going to need to figure out how many times you need to replace the air in the tent via your output fans.

For making this easy I think you should just be concerened about the output fans and let the intake be passive through the grow texts vent holes.

For instance a 4x4x7 tent has 112 cubic feet.
The measurement of exhaust (output) fans are in cfm. ( cubic feet per minute ).

So if you were to get this fan. Which is rated for 740 cfm.

Hurricane Inline Fan - 8 Inch | 745 CFM | High Performance, Commercial Grade Inline Fans, Quiet Operation - Ventilation Fan - ETL Listed https://www.amazon.com/dp/B006Z1JLN0/ref=cm_sw_r_cp_api_wrPSAbZ1FFYQK

And do some quick math.

740 x 60mins = 44,400 cubic feet of air moves per hour.


44400 / volume of room (112) = 396.5 times within that hour, that the grow room air is sucked out through the attic - and intaking the air in the room passively.

An important part to this scenario is that the air needs to be completely vented outside of the room.

This also assumes that you have this fan on at all times, and at full speed. These types of fans comes with fan controllers to lower cfms. You can also put a timer on the power to the fan to control how often you need it on.

Your solution to getting the heat out of the room lies within this information I’ve shared with you.

Also - all these calculations are rated for 8inch ducting. If you lower the width of your ducting, it can’t move as much air and all your calculations need to be factored by that.

I went with a 60W eBay chinese special like this is a nice starting option because it does include absolutely everything you need (except a water reservoir, I use a Coleman cooler) at a reasonable price. You can get it delivered to your doorstep and stay within your $2500 budget.

That being said, there were several initial pitfalls (like blowing fuses and melting switches) that were caused by some exceedingly poor documentation (and a little laser cutting inexperience on my part.) Once I worked out those initial problems, its been cutting reliably for us for the last 6 months with almost daily usage.

The only real upgrades we've done have been a water cooler (we grabbed a water refigeration unit for a large aquarium for $275) and an upgraded exhaust fan (the included unit was very loud).

Next on the list would be an adjustable air assist with a more consistent flow, but what the included air pump is works well enough.