# Starting to look at fans

Cleared room for the 4x8 tent, but now I’m concerned about ventilation. Bought a 4" fan & filter for the 2x2 tent but I want to be sure to get enough fan for the 4x8. Is there a rule of thumb for ventilation - like 50 watts psf for lights? A T80 looks nice, but will that be strong enough when pushing exhaust thru a filter?

### How to choose the exhaust/intake fan that best suits your grow room

Here is a simple calculation used by many growers:

Exhaust fan: Potential volumetric capacity of the fan (m³/h) = Volume of the active growing space (m³) x Air exchange time (hours) x Loss of efficacy.*

• Length by width by height of the grow room containing the equipment and the plants

As an example, let’s take a basic set up of 1.20 x 2.40 x 2.5 m (7,20 m3) with two 600 W HPS lamps .

Once you have calculated the volume of the growing area you just have to multiply it by the circulating air volume per hour . In indoor set-ups that are not air conditioned or CO2 -enriched, where one inch equals 1/minute, this is calculated by multiplying the volume of the growing space by 60 (minutes) .

Consider that if you are using a carbon active filter, this will cause a loss of efficiency of about 25 per cent of the potential capacity of the fan. Obviously, this will vary according to the diameter and the condition of the filter as well as to the length of the duct, but in any case 25 per cent is a fairly safe margin. The only thing you need to do is multiply the result by 1.25.

Potential volumetric capacity of the fan (m³/h) = (Volume of the active growing space (m³) x 60) x 1.25 , which gives you the minimum volumetric capacity required.

Minimum volumetric capacity required = ((1.2 x 2.4 x 2.5) x 60) x 1.25= 540 m3/h.

The above result is the minimum exhaust capacity of the fan in m3/hour, in this case 540 m3/h. That said, remember that, where possible, it is best to opt for higher performing models .

i use volume (in cubic feet) x 3 or 4 (magic fan factors) = ___ cfm.

assuming your 4x8 is 7’ tall…
4x8x7= 224 cu ft x 3 or 4 = 672 or 896 cfm of centrifugal or mixed flow fan needed.!
either one 8" or 10" or 2x 6" or 8"
what ever size u use put it on a speed controller.!!

I use (ft x ft x ft)/27 = approx m^3 to use above so if the tent is 6ft you would get (4x8x6)/27=~7.1 m^3 so you need a fan that can pump 532m3/hr (7.1 x 60 x 1.25) or 14364 cubic feet/hr

@jim44 I have this one, and highly recommend it. Extremely efficient, and extremely quiet. I had it in my 4x8 but downgraded to a 4x4, and it still kicks ass.

AC Infinity CLOUDLINE T6, Quiet 6” Inline Duct Fan with Temperature Humidity Controller - Ventilation Exhaust Fan for Heating Cooling Booster, Grow Tents, Hydroponics

https://www.amazon.com/dp/B074XBXFPD/ref=cm_sw_r_cp_api_i_g.hECb2YEFJ74

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