intake/exaust/smell question...experienced just need a little help

Ok so my room is going to be 5'L x 3'W x 3'H and i will be using two 400W MH lights. To control the heat that would be put on the plants i am going to insert a piece of glass underneath the lights to completely cut them off from the plants. Im going to use high-temperature kaulk all around the glass to make sure theres nothing leaking through at all.... this is the part that i know will work well...

My questions are:
1. since my exaust point is going to be inside the glass casing (heat chamber) there should be no smell coming from the exaust since theres no connection to the room... right?

2. Intake is a very important part because the plants need fresh air... if i use two fans to bring fresh air in will smell leak out from the intake holes into the room?

3. Is there anything im missing or overlooking?

I appreciate it... Im gonna go smoke and i hope theres plenty of responses when i come back

1. If you seal off the top than no there will not be any smell coming through
2. Yes smell will get out if you use two intake fans under the glass. That is going to create a positive pressure in the room forcing stinky air out of any hole or crack it can find

My question for you is...where is smell supposed to go? You need to have negative air pressure and a filter to cut out smell (at the least). Good rule of thumb is your intake air should be 1/4 of your exhaust. This gives great negative pressure and makes sure there are no leaks.

So 100 CFM's for intake would mean 400 CFM's for your exhaust/filter.

ok i think i get what your saying.... so i will need a sepreate exaust inside the box to nuetrualize the smell and create the right air flow.... that makes a little more sense..... and if my intake is 1/4 of my exaust no smell will leak out through the intake holes?

Dutchman24 said:

ok i think i get what your saying.... so i will need a sepreate exaust inside the box to nuetrualize the smell and create the right air flow.... that makes a little more sense..... and if my intake is 1/4 of my exaust no smell will leak out through the intake holes?

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I believe AlBfuct once wrote in a thread You simply just need to cut a hole a certain size in the wall of the room and the negative pressure created by the exhuast fan will simply suck fresh air inside the room. There was a formula to figure out the size of the hole need to be cut that he posted.. i believe you needed you exhaust fans actual CFM and room size. If you seach through his thread( I know it long) you can find the formula... hope that helps

Right, I am so used to larger spaces. The 4x4 I am in now is even small for me compared to what I am used to (few plants in an open space). As long as your exhaust fan can replace the air in your room every 5 minutes you should be fine. I would think that you would want the intake hole to be the same size as the hole you are exhausting through. So if you have a 6 inch filter/exhaust, the hole in the other side (intake) should also be 6 inches in diameter.

That's just a guess on my part however. You should probably hunt through the aforementioned thread.

Wouldn't the exhaust have to be on 24/7 this way though? I mean, if it shuts off for any amount of time you have a hole in the side of your box that will allow smells to leak out, no?

To figure out how many CFM's you need for exhaust, you would figure out the cubic feet of your grow space. That's how much air you need to move. So if you have 400 cubic feet of grow space, you need a fan thats rated for 150 CFM's or so.

Yea i was just looking around and one guy posted this.....
The correct volume of air to move will be 1/3-1/2 of the room volume per minute. Proper air exchange should be able to take place in 3 mins. My room is a bit over 800ft3 and I use a 400cfm (dialed down to about 300cfm)fan. Perfect.


And as for the size of the holes:

Your intake needs to be equal size or larger by 50%. This will still keep you under negative pressure, allow proper mixing of the air before exhausting. It would actually be impossible to move more air through the exhaust than the intake can bring in because if the fan is 435cfm, then you move 435cfm or less (depending on quality of fan). It could be done by using an intake fan but that is not going to keep you under negative pressure and it will pressurize the room, leaking smells all over.
Thanks for all the help... that just helped me out hugee

My room is 45 cubic feet and my fan is rated for 80 cfm... would having to much air movement hurt the plants


and what about placement of the exaust/intake... would it be better to have the exaust directly above the intake hole or have them at opposite sides of the room

Dutchman24 said:

My room is 45 cubic feet and my fan is rated for 80 cfm... would having to much air movement hurt the plants


and what about placement of the exhaust/intake... would it be better to have the exhaust directly above the intake hole or have them at opposite sides of the room

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More air flow shouldn't hurt them as long as it is not ridiculous, or blowing straight on them (get wind burn). One thing you will find is that your plants will transpire (sweat pretty much) a lot faster with more air flow...resulting in you needing to water more often. No biggie.

As far as placement of intake/exhaust goes. I would have the intake low to bring in colder air (below plant level ideally) and the exhaust in the upper (above plant level) opposite side of the box. That way air moves across the room and over/through your plants.

Ever Hear of Gonzo. Its a bag of crystals that are charged by (none other than) LIGHT. so when the lights come on they kill more skunk smell and they stay charged for 24 hours killing smells even after the lights go out.. bought mine at the depot

Thanks i was thinkin the same thing i think i'll put them at opposite sides of the room..... and yea ive used gonzo before it def works good... using a filter with gonzo in the room and theres no problem with smell.

Any thoughts on the best way to stop light from escaping and coming in the ventilation holes?

Medical User said:

Ever Hear of Gonzo. Its a bag of crystals that are charged by (none other than) LIGHT. so when the lights come on they kill more skunk smell and they stay charged for 24 hours killing smells even after the lights go out.. bought mine at the depot

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I have a buddy of mine that self dubbed his grow a "ghetto grow." He has had some odor issues, I think I may have to tell him about these.

Dutchman24 said:

Thanks i was thinkin the same thing i think i'll put them at opposite sides of the room..... and yea ive used gonzo before it def works good... using a filter with gonzo in the room and theres no problem with smell.

Any thoughts on the best way to stop light from escaping and coming in the ventilation holes?

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Ducting! You can just get the right sized ducting for your intake, and then run a few feet so that light etc has to at least go around a corner or two. May reduce air flow a bit, but your fan is a little large anyway right?

Yea so far all ive really seen is using some duct and spray painting the inside black.... the overpowered fan should still be able to pull the right amount of air though if i manage to only make 1 or 2 bends

Make sure to put some kind of cheese cloth, or screen of some sort over your intake duct. Keeps little nasty crawly things out....as well as dust bunnies.

statik said:

Make sure to put some kind of cheese cloth, or screen of some sort over your intake duct. Keeps little nasty crawly things out....as well as dust bunnies.

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Black panty hose work well too because they keep some light out as well

tom__420 said:

Black panty hose work well too because they keep some light out as well

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Not only that, but they also grip the ducting great..and sexy to boot!

I am actually using an old pair of my wifes panty hose on my intake....not black though.

nordowell said:

get a cooltube.

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Dude, I see where you are going with that I think. He would be able to help eliminate heat by pulling air over the bulb. Connect the fan to the reflector, and the filter to the fan on the outside (assuming you dont have room for it inside).

That way you are using one fan for cooling your light, intake, and exhaust/filter. Would also mean no reason to have that extra glass/caulking (heat chamber).

Wouldnt be hard to do at all actually. Just have to upgrade the fan. Prolly would have to do that anyway actually. Adding a filter is going to reduce air flow for sure.