What Intake?

If blowers are preffered for Exhaust, then what would I use for intake?? And do I install them on the inside or outside with duct pipe going into the hut?

Yes, I'm using a hydrohut mini...

CFM?? W' x L' x H' right?

If you exhaust the air from a space, then the air pressure will have to equalize and air will be pulled in through every opening. It's like Science. That's called a passive intake, meaning you aren't actively pushing air in. You must provide enough openings for the air to come in, tho.

The LxWxH is how you figure cubic feet of your area. Your fan is rated in Cubic Feet per Minute it will move. You should get a fan that will change the air in your space at least once every 3-5 minutes.

HTH

To add to potroast's data, I find that an effective passive intake should be around double the area of the exhaust fan ducting, i.e. 2x 10" dia passive intakes per 10" dia exhaust fan.

For better scent control, powered intakes should be slightly smaller than the exhaust. If the intake fan and exhaust are identical, the intake can be run on a speed controller to 90% normal speed. This runs the room at a slightly negative pressure compared to atmosphere. If you have lined a room tightly with plastic film, it will blouse inward slightly. All air exiting a room at negative pressure goes via the exhaust blower, where it can be effectively scent treated with a carbon filter or ioniser.

If there is more intake air capacity than exhaust, various air leaks will exit wherever they can find a path. Much harder to control scent from a bunch of small leaks.

ok, i have two carbon scrubbers with fans attached approx. 200 cfm each.. what should i buy for an intake fan? 265 cfm? 469cfm? 100cfm?

dreamorigami said:

ok, i have two carbon scrubbers with fans attached approx. 200 cfm each.. what should i buy for an intake fan? 265 cfm? 469cfm? 100cfm?

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Your 2 exhaust fans move 400CFM. The carbon filters will reduce the exhaust rate a bit. The intake should be about 10-15% less than the 400CFM figure.

i found a 60cfm Hydrofarm cooling exhaust blower fan... could that work for my intake? what i want know is can i use the ecoinline fans? they mention exhaust in their descriptions and that's throwing me off. i'm trying to buy the right thing so i don't waste my time or money. thanks

potroast said:

If you exhaust the air from a space, then the air pressure will have to equalize and air will be pulled in through every opening. It's like Science. That's called a passive intake, meaning you aren't actively pushing air in. You must provide enough openings for the air to come in, tho.

The LxWxH is how you figure cubic feet of your area. Your fan is rated in Cubic Feet per Minute it will move. You should get a fan that will change the air in your space at least once every 3-5 minutes.

HTH

Click to expand...

That's exactly what I'm building right now. Actually I'm cutting a hole in the ceiling and running duct work through the roof. Then on the door of my closet up cutting a hole towards the bottom with a curved vent so you can't see the light. 80 cfm fan with a can 9000 carbon filter. I only have a 200 cubic foot area I'm clearing....every 2.5 minutes.

SmokerE said:

80 cfm fan with a can 9000 carbon filter. I only have a 200 cubic foot area I'm clearing....every 2.5 minutes.

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Your fan will be underpowered for that size volume grow room.

Optimally you should exchange the air in your growspace about once every 3 minutes. 200/3 = 66.6cfm. You need to add at least 20% for a carbon filter, 66.6 x 20% = 13.3+66.6 = 79.9 cfm + allowances for ducting kinks and air resistance add 20%, plus allowances for un-air-cooled hoods add 10-15% per non-air cooled hood, add 25% for hot climates and 40% for hot and humid climates.

Not hard to see how under-powered your 80cfm exhaust fan is going to be. My space is 6 ft by 2.5 ft by 1.5ft = 22.5 cubic feet, I run a 110cfm exhaust fan in there at 50% speed most of the time and I find it keeps my temperatures nicely under control.

You, are going to need to get yourself a somewhat larger fan.

I'm sorry my math was off. I did have it figured out right when I purchased it. 7 ft. X 3.5 ft X 3.5 ft. Roughly 85 cubic ft.

Alright someone told me passive was the way to go and explained how to do it.. just stick 2 feet of duct into my hydro hut and that's it.. i don't need a fan

hey babygrow,

what kind of fan are you using. also what kind of filter? I am currently building a box and could use a little help.

LERecords said:

hey babygrow,

what kind of fan are you using. also what kind of filter? I am currently building a box and could use a little help.

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Systemair RVK100 4 inch 175m3 an hour inline fan.
Carbon filter is a standard carbon filter designed to work with the airflow of the fan I'm using.

What kind of help do you need?

dreamorigami said:

they mention exhaust in their descriptions and that's throwing me off.

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There's no difference between a fan used for intake or one used for exhaust, other than what you call it due to where you're using it.

You do have to get the flow capacities correct for your room's size- that's all.

Exhaust fans get mounted up high in the room as warm air rises. Intakes are mounted near the floor and as far away from the exhaust as possible.

babygro said:

You need to add at least 20% for a carbon filter, 66.6 x 20% = 13.3+66.6 = 79.9 cfm + allowances for ducting kinks and air resistance add 20%, plus allowances for un-air-cooled hoods add 10-15% per non-air cooled hood, add 25% for hot climates and 40% for hot and humid climates.

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Great detail, bg.

If one has to push air through a long duct, through 90 degree bends or carbon filters, it's better to select a centrifugal blower rather than an axial (typical fan blade) type.


Centrifugals have smaller gaps between the impeller blades and the fan housing and can develop some good pressure on the outlet.


When axial fans encounter backpressure, the pressure leaks backward through the gaps between the fan blades. However, axials are perfectly suitable for most ventilation applications where backpressure or flow restriction isn't a problem.

was just looking to see what fans you were using.. thanks