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What Type Of Cooling Fans?


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I think you will be fine with just air circulation a 400 watt lamp stays pretty kool so just go to walmart and buy a $15 oscillating table fan and convert it to a wall mount by putting a screw through the base and flipping it upside down .




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use a canfan 6in and the speedster 4 variable speed :sword:


Not a bad setup...if he is planning on tripling his grow size! lol. Putting a 6" inline in a setup that size is like buying a Ferrari to commute to your job. Sure, it would work great, but it is a bit of overkill...


Really, it isn't like you can have too much circulation, butI tend to agree with the poster who said you'd be good enough with just an oscillating fan. IMHO, for a grow this size, you'd be much better off to take the money you'd spend on an inline fan and invest it in other areas, like lights and nutrients. At the very least you'd get more bang for your buck.

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Howdy, I have a 36"x30"x60" grow box and i will be using a 400 watt bulb, what fans for cooling that space would you say to use...and how many cfm does a 120mm computer fan have? thanx, migreen


Can't say based on info given. Depends on vent system (if any)? Door? Closed in ? Left open? Where is the room? etc.


If it's all closed in on a second floor with poor air supply/vent, a 400 in that little space will be too hot, fan or not.



If it's a basement, different solution.

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well, the box is in the basement, 65 to 68 degrees, no holes cut yet, open to suggestions...36x2.5x60= 37.5 cubic ft..according to some here i need at lease that in cfm to replace the air once in 5 min i think and 112.5 cfm to replace the air 3 time every 5 min...my question is what type of fans for top and bottom do i use..or can i guess drill holes in the bottom side for the intake and dump the heat out from the topwith some type of fan pos a pc 120mm

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I found this post on another site. Pretty accurate and helpful.





There are many calculations on the web for sizing a fan for ventilating grow rooms; however, what these calculations fail to take into consideration is the friction loss on carbon filters, increased temperatures from HID lights and CO2, etc. The following calculation can be used as a guide for sizing an exhaust fan for a growing area (keep in mind that this calculation will give you the lowest required CFM required to ventilate the grow room):




Step 1 – Room Volume


First the volume of the room needs to be calculated. To calculate multiply length x width x height of growing area e.g. A room that is 8' x 8' x 8' will have a volume of 512 cubic feet.


Step 2 – CFM Required


The fan should be able to adequately exchange the air in a grow room once every three minutes. Therefore, 512 cubic feet/3 minutes = 171 cfm. This will be the absolute minimum cfm for exchanging the air in a grow room.


Step 3 – Additional factors


Unfortunately, the minimum cfm needed to ventilate a grow room is never quite that simple. Once the grower has calculated the minimum cfm required for their grow room the following additional factors need to be considered:


1. Number of HID lights – add 5% per air cooled light or 10-15% per non-air cooled light.


2. CO2 – add 5% for rooms with CO2 enrichment


3. Filters – if a carbon filter is to be used with the exhaust system then add 20%


4. Ambient temperature – for hot climates (such as Southern California) add 25%, for hot and humid climates (such as Florida) add up to 40%.



Inline duct fan 800 cfm


Example 1:


In our 8’ x 8’ room we have 2 x 1000w air cooled lights, and we plan to use a carbon filter. We also plan to use CO2 in this room. The ambient temperature is 90°F, however, we will be using air from another room that is air-conditioned.


Minimum Required CFM to ventilate room:


(CFM required for room – step 2) + (CFM required for room – step 2 x 10% (2 air cooled lights)) + (CFM required for room – step 2 x 5% (CO2)) + (CFM required for room – step 2 x 20% (Carbon Filter)) + (Ambient Temperature 0 (Air coming from air-conditioned room)).


= (171cfm) + (171cfm x 10%) +

(171cfm x 5%) + (171cfm x 20%) + ( 0 )


= 231cfm – this is the absolute minimum cfm required to ventilate your room.




The next step would be to match the closest fan to this CFM. As we are using a carbon filter we will need to match the fan with the filter so that the fan that will neatly fit onto the filter. The filter that we will use is a Dutch Breeze Carbon Filter - DFS4. The DFS4 has a 6" flange. Our options for 6" fans are as follows:


- Eco Plus 6” – 440cfm


- Fantech 6” – 252cfm


- Fantech 6” XL – 392cfm


- Elicient 150B – 309cfm


The DFS4 filter has a cfm rating of 255-309, so the fan that we will choose for our room will be the Elicient 6” fan. This will be an ideal fan for this room and carbon filter, since the extra cfm will help compensate for the small amount of ducting we may have to run.


If only step one and two was used (the calculation that is most commonly displayed on garden websites) then the grower would have chosen a 4” fan and a 4” carbon filter; the grower would have soon found out that this fan and carbon filter would have been inadequate for their grow room.




Example 2:


If all the variables are kept the same and we changed the room size from 8’ x 8’ to a 12’ x 12’ then the minimum required CFM would be 519 cfm, thus the fan would be Fantech 8” XL, Elicient 8” or EcoPlus 8” and the DFS5 or DFS6 Dutch Breeze carbon filter.


The Really Simple Method:


If you want to keep things really simple, just remember that you want to replace the air in your grow room every one to three minutes. If you're in a hot area, exchange it every minute; if you're in a cooler area, you can take up to three minutes.


The Very Important and Often Overlooked Intake Port




It is very important to understand that you can't simply put an exhaust fan in a sealed room and expect to suck air out of it. You absolutely must have some kind of opening in the room to allow fresh air to replace the air you are exhausting. If you don't understand this concept, just put your finger over one end of a straw and try sucking out of the other end - you'll find that the walls of the straw collapse inward and that you can't suck any air out. If you were to poke a small hole somewhere in the straw, you will find that you can now suck air through it; the bigger the hole, the more air you can suck. Obviously, any fan you install in your grow room isn't going to be powerful enough to create enough negative pressure to suck the walls inward, but what will happen is that your fan will draw more energy, make more noise, run hotter, break down much sooner than it should, and finally, suck very little (if any) air out of the room. An intake port can be anything from a gap under the door to an open window - even a hole in the wall. The best place for an intake port is diagonally opposite from your exhaust fan; that way, air has to pass across the entire room - very efficient. You can put a piece of screen over the opening to keep insects and animals out, a piece of A/C filter to keep dust out, or a Louvered Shutter or Backdraft Damper that opens when the fan turns on and closes when it turns off. You can also use a Motorized Damper. This gets installed in-line with your ducting and is plugged into whatever device controls your exhaust fan. When your fan turns on, it allows air to pass. When your fan shuts off, it seals completely, preventing CO2, air, odor, etc. from passing. You can get creative with these devices and use one fan to control two rooms, etc.


One last note about intake ports - you will see much better results from your exhaust system if you install a second fan to create an active (as opposed to passive) intake system. Normally, when your exhaust fan sucks air out of your room, air is passively going to get sucked back into the room. By installing a second fan on the intake side, you will reduce the amount of negative pressure created in the grow room, thereby cutting down greatly on the amount of work the exhaust fan has to do and allowing much more air to pass. Ideally, the intake fan should be the same size as the exhaust fan, but it can be a little smaller if necessary. If you're not sure or you don't want to spend the money, start out with just an exhaust fan. If it's not performing as well as you thought it would, try adding an intake fan - you'll smile when you see the difference!


Fan and Carbon Filter Placement




If no carbon filter is being used then place the fan at the highest possible point in the room; the reason for this that hot air rises and it is the hot air that needs to be exhausted. Also, place the fan on the opposite side of your intake. The negative pressure that the fan creates in the room will pull air from the intake opening across the garden and towards the fan. This will bring the fresh air over the plants while displacing the old stale air.


If a carbon filter is being used then place the fan on top of the filter. There are two options that a grower can use with the carbon filter: 1) Suck through the filter or 2) Blow through the filter.


Sucking air through filter is the preferred method. Carbon filters should be placed on the floor standing upright or hung horizontally from the ceiling. Place the fan and filter in the room opposite the intake port. From the fan, attach ducting so as to exhaust the scrubbed air out the room. Keep the ducting as short as possible and avoid any bends in the ducting. Keeping the ducting as short and as straight as possible will reduce the friction loss and noise.


Blowing through the filter is a less commonly used method of exhausting. The benefit is that the fan can be placed at the highest point in the room and the hot air is sucked out of the room and forced through the filter. However, if you're using the fan/filter combination as part of your exhaust system (as opposed to just an odor scrubber), it will need to be placed outside of the growing area.


Before using a carbon filter for the first time always take the filter outside and then first suck, then blow through it before installing it in your growing area. This will blow out any carbon dust which is created in the filter during transport. During normal operation always keep the dust sock on the filter; this stops large dust particles from blocking the filter and will help prolong the life of the filter.


Air Circulation




Always provide your plants with adequate air movement and circulation in the grow room. Air circulation within the room eliminates stale spots and also reduces the formation of micro-climates within the leaf canopy. If air circulation in the grow room is poor then the micro-climate in between the plants increases in humidity and temperature. This can result in mildew and insect problems, as well as less deficiencies. For adequate air circulation use a wall mounted fan; 2-3 fans will provide sufficient air movement. Never switch these fans off unless you are spraying or fogging your room. Good Luck everyone!

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Ok so here's a diagram of what I'm thinking. Again, very new at this please don't rip me. As I thought about this closed system I read where leaves need to breath. I think it would be a great CO2 system but then again I'm not sure of other issues.




Now addressing the breathing issue. An open system at the bottom would work and is installed on most cabinets I have seen. I can't see CO2 working with this but I'm not going to be working with CO2 now anyway. Does this create other issues like smell coming from those vents? Is there a bigger problem controlling temperature this way? I have a feeling temperature is going to be an easier fix over the humidity. Would both senors be tied into each other so if the Humidity gets to 80-85% the fans kick on. When temperature falls to 70ish they turn off?




Please let me know if I'm missing a major or minor component. Thanks

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well, the box is in the basement, 65 to 68 degrees, no holes cut yet, open to suggestions...36x2.5x60= 37.5 cubic ft..according to some here i need at lease that in cfm to replace the air once in 5 min i think and 112.5 cfm to replace the air 3 time every 5 min...my question is what type of fans for top and bottom do i use..or can i guess drill holes in the bottom side for the intake and dump the heat out from the topwith some type of fan pos a pc 120mm


Basement is always good. Doesn't get too hot. Doesn't get too cold. The box is so small that you could probably get by without an exhaust fan. IF you are budget constrained, simply put a vent in the top and a small fan inside the box and leave the door open. Fresh air drifts in, heats up and rises out the top. You can regulate temp by how far you leave it open. This is OK for veg. and then you shut the door and close the vent when you are on the dark period for flower. Insulate it so the heats stays in and keeps temp at 65-70 during dark. That's the "on the cheap" way. Winter may bring an obstacle of low temp at dark periods, but if insulated, you can keep it warm with heat mats because it is so small. Cheap and easy, but requires monitoring.


Now if you don't have time to watch it and want it all automated and have some extra cash, then you stick a fan in the top hole, a fan in the bottom hole, put them on thermostats, leave the door closed, etc.


If are doing CO2, need outside air, need odor control, heater for winter, etc. then you add $$$, work time, and complexity.


It's so small, I wouldn't worry about CFM..blah blah blah. You want the SMALL ones.

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