Ventilation: Air in and Air out question.

[Gazza2001au]

As Indy suggested it is always good to have more air movement than needed and back off the fan speed, all sorts of things happen especially if u build your room in winter or the cooler months and plan on growing year round u end up running into complications when it warms up

 

i have in winter used 2x 120mm Sunon fans one for intake one for extraction but i was only running a 175w MH than the weather warmed up and i found it very difficult to control temps but back than i was on a very limited budget and fans cost a lot of money in those days

 

mould is the biggest problem with picking the right ventilation fan, adding a intake fan will increase your air exchanges by a lot more than just running a passive intake with one exhaust fan

 

don't forget if your in a room a pedestal fan can redirect all your heat from hid lights as does a tower fan in a tent but without either the air your exhaust fan sucks thru passively will take the less resistance path so u may have hot pockets of air,think like the wind use a long piece of hair or piece of sewing cotton string than start up your ventilation and walk around the room holding the string by one end u should see the air movement in the room moving the string it will give u a indication where u will possibly have stagnant air in the room it will also show u the path your air is going thru the room if u don't have string or long hair use something light and thin like that crinkly shit u use for kids easter hat parades

 

but u could just buy a air conditioner and a humidifier,a window air con only draws 500-750watts

[joe.citizen]

Thanks Gazz, I'll take that on board mate.  The heat shouldn't be too much of a prob as it doesn't get super hot where I am, and the CMH lights don't produce any where near what MH and HPS lights do so should be all fairly managable - more concerned with the CO2 replenishment and humidity control.

[Gazza2001au]

Joe u need around a 1000m3 per hour fan thats sufficent to exchange the air in a 3x2x2.4m room once every minute than u just need to focus on humidity

[joe.citizen]

Also, I usually have flyscreen on my intakes for obvious reasons, and if you have dusty conditions in your area those screens can block up quite a lot and restrict the flow noticeably. Usually cleaned the screens every 10-14 days. Use to run the fan 24/7.

Any advice on how much passive intake I’ll need for 300mm max-fan? Would 2X 200 mm intakes be sufficient? Cheers!

[Indycar]

Last time I ran a 300mm centrifugal fan. I had it drawing 1x150mm in a veg cabinet, and the flower cab was drawing through 2x200mm intakes. That seemed to have worked just fine, but I did have some bends in the ducting which does reduce flow, having that sort of worked to my advantage.

 

But say if you're drawing 2x200mm intakes in a tent through a 300mm centrifugal fan with little resistance with the ducting. That passive intake might be inefficient, may require 3x200's which might be closer to optimum. Though if you had a fan speed controller, I'd reckon you'd be able to dial it down to what you require.