Another Ventilation Question

G

grreen

Member
I am currently building a 3ft x 3ft x 6ft grow box and running a 400 watt hps in it.

Would a 400++ cfm duct fan be enough to bring the temperature down to room temp? The following is the duct fan I am intending to buy:

http://www.vent-axia.com/products/commercial/acp.asp

Lastly are intake fans necessary? Can I just cut some 4 inch holes and mount a 90" pipe to block out the light.:confused:
 
Hairy Bob

Hairy Bob

Well-Known Member
That fan looks good to me, should easily keep a 54 cubic ft room in temp ranges, but you might wanna watch the humidity, don't let it get too low as it can cause stress. Until the last couple of weeks 50-60% is ideal but if it stays above 30 you should be ok. In the last two weeks of flower you want it low to increase resin production.
It might be a good idea to have a fan speed controller, or a thermostat so the fan either runs at less than full speed, or only comes on when the temp gets above x degrees. Fwiw I do both. Wire a speed controller in parallel with a thermostat, and it will run at the reduced speed until the temperature rises and kicks the 'stat in, then the fan runs at full speed until the temp drops again.
Intake fans are a complete waste of time, money and energy. If you have a decent exhaust fan (which every growroom should) then it will lower the pressure in the growroom, forcing air in from outside, and keeping all the smells from leaking out.
The best an intake fan can do is move the same amount of air as would flow in freely, wasting energy. If an intake is too small, it can restrict the flow of air into the room, too large and it can raise the pressure inside the room creating odour leaks or, if the room is sealed, raising the temperature.
 
G

grreen

Member
Hairy Bob said:
That fan looks good to me, should easily keep a 54 cubic ft room in temp ranges, but you might wanna watch the humidity, don't let it get too low as it can cause stress. Until the last couple of weeks 50-60% is ideal but if it stays above 30 you should be ok. In the last two weeks of flower you want it low to increase resin production.
It might be a good idea to have a fan speed controller, or a thermostat so the fan either runs at less than full speed, or only comes on when the temp gets above x degrees. Fwiw I do both. Wire a speed controller in parallel with a thermostat, and it will run at the reduced speed until the temperature rises and kicks the 'stat in, then the fan runs at full speed until the temp drops again.
Intake fans are a complete waste of time, money and energy. If you have a decent exhaust fan (which every growroom should) then it will lower the pressure in the growroom, forcing air in from outside, and keeping all the smells from leaking out.
The best an intake fan can do is move the same amount of air as would flow in freely, wasting energy. If an intake is too small, it can restrict the flow of air into the room, too large and it can raise the pressure inside the room creating odour leaks or, if the room is sealed, raising the temperature.
Click to expand...
I guess its better to err on the safer side by having a smaller passive intake hole? What size do you suggest will a 4 inch hole be enough?:confused:
 
Hairy Bob

Hairy Bob

Well-Known Member
You do want it slightly smaller, yes. Are you getting the 6" fan? If so a 4" hole won't be enough unless your box is leaky. The area of a circle with diameter 4" is about 12.5sq in, 6" diameter is about 28sq in. Two would be ok, or one hole about 5 1/2"
 
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