Smell seeping out - Need better fan?

[ATrueBlackThu]

Gf says she can smell the pot even when I haven't opened the tent yet today so I need this fixed ASAP.

I currently have two fans in my tent, intake and exhaust. I believe they are both rated at 100 cfm. Could my problem be that the exhaust simply isnt strong enough to clear the tent before the smell seeps out the cracks? If so should I just get a 190cfm exhaust fan? Hopefully I don't need to upgrade to a bigger carbon filter too.

The tent is 48x24x72

 

[TWINTURBODOGO]

We have the same size tent and use an inline fan rated at 300cfm dialed back on a speed controller.
We also have a passive intake, we use the vents in the tent to bring in fresh air. The exhaust fan pulls in enough air to create a vacum.
I've seen odor neutralizing gell like stuff you can buy. Never used one though.

 

[TripleBeam]

A carbon filter will solve that problem. I was skeptical carbon filters did the job but I was happily surprised when I installed mine and the smell is GONE. I bought a 6 inch 440 cfm inline fan with the speed controller and a 4 inch carbon filter. Doing so allows me to keep the fan speed low and the noise while having plenty of air power to ensure the filter works properly. My tent is a 5x5x6.5.

 

[TheFertilizer]

Gf says she can smell the pot even when I haven't opened the tent yet today so I need this fixed ASAP.

I currently have two fans in my tent, intake and exhaust. I believe they are both rated at 100 cfm. Could my problem be that the exhaust simply isnt strong enough to clear the tent before the smell seeps out the cracks? If so should I just get a 190cfm exhaust fan? Hopefully I don't need to upgrade to a bigger carbon filter too.

The tent is 48x24x72

Get a slower intake fan or nix it all together. As twinturbo pointed out a strong exhaust fan will create a negative pressure inside the tent, not technically a vaccum, but you will visually be able to see the tent walls suck in and in that state there's more air flowing into the tent and then being scrubbed than there is any getting out. With your intake, it's blowing in enough air to make it more neutral and probably actually positive because the intake is rated the same as your exhaust but without a filter attached, so you're getting more intake more in than you're exhausting.

 

[ATrueBlackThu]

Get a slower intake fan or nix it all together. As twinturbo pointed out a strong exhaust fan will create a negative pressure inside the tent, not technically a vaccum, but you will visually be able to see the tent walls suck in and in that state there's more air flowing into the tent and then being scrubbed than there is any getting out. With your intake, it's blowing in enough air to make it more neutral and probably actually positive because the intake is rated the same as your exhaust but without a filter attached, so you're getting more intake more in than you're exhausting.

I did start without an intake fan but the smell was leaking out then as well, I thought adding an intake and closing the flaps would stop the smell but I was wrong. I guess ill just have to buy a stronger exhaust fan. Unfortunately the fans and filter are only 4" sothat really limits it for me

 

[Croatsan]

You can use the adapter from 4'' to 6''. No?

 

[TheFertilizer]

You can use the adapter from 4'' to 6''. No?

Yeah that's what I would do. They're called reducers, should be available at your local hardware store. It won't lower the air flow rate, but it will increase the pressure, which will probably cause more drag on the ducting and more noise but otherwise should be the same.

 

[TripleBeam]

which will probably cause more drag on the ducting and more noise but otherwise should be the same.

I found that the exhaust is very quiet. The reducer I bought was metal but didn't cause any additional noise. Using insulated ducting will also bring down noise. Don't forget the speed controller.

 

[Gorgar]

I currently have two fans in my tent, intake and exhaust. I believe they are both rated at 100 cfm. Could my problem be that the exhaust simply isnt strong enough to clear the tent before the smell seeps out the cracks? If so should I just get a 190cfm exhaust fan? Hopefully I don't need to upgrade to a bigger carbon filter too.

First, it sounds like you've been given some very good advice from TWINTURBODOGO and TheFertilizer about getting a better exhaust fan. As TheFertilizer mentioned, you will know that you're pulling enough air when your tent starts to suck in.

I think that you said that you have two 4" fans. They sound like those duct booster fans to me based on your indicated flow rates, but I don't know. That type of fan has its' limitations and really does not make a good exhaust fan, especially when you have to pull air through a filter. So the suggestions to get a better exhaust fan are solid.

But...and this is a big but...it could be worth a try to get a 4 inch 'Y' connector from HD (it looks to me like they carry them in-store) and using your existing two fans to pull the air through the filter. You might need some duct tape or something because it uses crimped ends (like metal ducting does). That way you'd have two exhaust fans and use the passive air intake(s).

I'm not really recommending this approach, but for 11 bucks it might be worth a try. Good luck!

 

[TheFertilizer]

First, it sounds like you've been given some very good advice from TWINTURBODOGO and TheFertilizer about getting a better exhaust fan. As TheFertilizer mentioned, you will know that you're pulling enough air when your tent starts to suck in.

I think that you said that you have two 4" fans. They sound like those duct booster fans to me based on your indicated flow rates, but I don't know. That type of fan has its' limitations and really does not make a good exhaust fan, especially when you have to pull air through a filter. So the suggestions to get a better exhaust fan are solid.

But...and this is a big but...it could be worth a try to get a 4 inch 'Y' connector from HD (it looks to me like they carry them in-store) and using your existing two fans to pull the air through the filter. You might need some duct tape or something because it uses crimped ends (like metal ducting does). That way you'd have two exhaust fans and use the passive air intake(s).

I'm not really recommending this approach, but for 11 bucks it might be worth a try. Good luck!

That actually sounds like a really good idea to me. I didn't notice the 100 CFM rating quote either I thought he had two 190 CFM fans.

Yeah those booster fans, the thing about those is the CFM rating they're advertise as having is actually rated as if they were operating in line with another fan. That's why they're called "booster" fans. The actual CFM rating of them could be a lot less, and on top of that they don't really handle pressure very well so drawing through your carbon filter is a big job for them. If you hooked them both up side by side in a Y connector they MIGHT do a better job. It's really up to you if you wanna gamble the 11 bucks.

I'm pretty confident one 190 CFM fan would do the trick in a tent that size. My 4x4 is about twice that size, maybe a little more since I'm pretty sure it's taller than 72 inches but otherwise half sounds about right, and at 400 CFM my fan creates a significant negative pressure in there. At half the speed it still does so I would expect that at that volume that 190 CFM would be fine.

 

[ATrueBlackThu]

Ill just go ahead and buy a better fan. I really liked the idea of using a y pipe but I still prefer having an intake because it would be easier controlling the light that way. And its only a $4 difference between the 4" and 6" so might as well just go all out i guess.

When first buying this stuff I just never thought about the negative pressure

 

[TorturedSoul]

I agree with others about nixing the intake fan. That could be half (or more) of your problem. Install an EXHAUST fan that is capable of exchanging your tent's volume 3x/minute (which would equate to 144 cubic feet per minute) under load. Higher if you wish to use a speed-controller. Centrifugal fans are not, as a rule, meant to move air against/through restrictions such as carbon filters (if you find one that is rated for this, it'll be clearly stated - both in the specifications and the price, lol) and, therefore, the actual CFM would be appreciably less than the rating.

Potential reasons for "stink" are: Your carbon filter is undersized. The carbon material needs refreshed/changed. Exhaust fan is not capable of sufficient CFM. You installed an intake fan, which is interfering with the common sense approach of having a negative pressure environment inside your tent, which is causing air to be forced out through any pinholes, seams, and other non-airtight areas of your tent (such as unused ports, vents, et cetera) along with any gaps/etc. in your exhaust "after the filter but before it exits the tent."

Lose the intake fan. Install an adequate exhaust fan. OPEN your tent's intake vents... You want just enough airflow through them that they keep your tent from being "collapsed" by the exhaust fan, yet still show evidence of a slight negative pressure (walls will suck in slightly). A 6" fan, filter, and duct run is less restrictive than 4". A four-inch can work, but you would want to allow for the extra restriction when sizing it; you may have to adjust your intake vent(s) in order to achieve this. The proper way to overcome restrictions is NOT by adding an intake fan and using it to try to "push" air through the system, lol - as you have discovered, this is folly, and air (like most everything else) will take the path of least resistance.

 

[Gorgar]

Lose the intake fan.

 

[TheFertilizer]

I agree with others about nixing the intake fan. That could be half (or more) of your problem. Install an EXHAUST fan that is capable of exchanging your tent's volume 3x/minute (which would equate to 144 cubic feet per minute) under load. Higher if you wish to use a speed-controller. Centrifugal fans are not, as a rule, meant to move air against/through restrictions such as carbon filters (if you find one that is rated for this, it'll be clearly stated - both in the specifications and the price, lol) and, therefore, the actual CFM would be appreciably less than the rating.

Potential reasons for "stink" are: Your carbon filter is undersized. The carbon material needs refreshed/changed. Exhaust fan is not capable of sufficient CFM. You installed an intake fan, which is interfering with the common sense approach of having a negative pressure environment inside your tent, which is causing air to be forced out through any pinholes, seams, and other non-airtight areas of your tent (such as unused ports, vents, et cetera) along with any gaps/etc. in your exhaust "after the filter but before it exits the tent."

Lose the intake fan. Install an adequate exhaust fan. OPEN your tent's intake vents... You want just enough airflow through them that they keep your tent from being "collapsed" by the exhaust fan, yet still show evidence of a slight negative pressure (walls will suck in slightly). A 6" fan, filter, and duct run is less restrictive than 4". A four-inch can work, but you would want to allow for the extra restriction when sizing it; you may have to adjust your intake vent(s) in order to achieve this. The proper way to overcome restrictions is NOT by adding an intake fan and using it to try to "push" air through the system, lol - as you have discovered, this is folly, and air (like most everything else) will take the path of least resistance.

Curious about how "slight" you're talking for the walls to come in, I have always been surprised by how much mine sink in. If you were to measure the deepest point of the wall it would be 3 inches deep from the sides where the poles are. Makes the tent look less like a cube and more like a... Well some kind of weird polygon lol

I put cut to fit filters on my tent's vents so I think that might be way my air flow in is so reduced, but it sucked the walls in quite a bit even without the filters attached. I think a lot of it will depend on what material the tent uses and how much slack there is in general, because if it's flimsy it will get sucked in by the same negative pressure more than a thicker fabric would.

 

[TorturedSoul]

Curious about how "slight" you're talking for the walls to come in, I have always been surprised by how much mine sink in. If you were to measure the deepest point of the wall it would be 3 inches deep from the sides where the poles are.

I would think any visible sign would denote a negative pressure. Err... You can have the stinkiest bowel movement in the history of the universe and, if the window is open with a fan sitting in it blowing out, you probably won't be vomiting from the smell whilst standing in the hallway outside the bathroom afterwards, because air is moving past you into the bathroom.

Okay, it's not quite that simple. But as long as your exhaust fan is moving enough fresh air through your tent to exchange the air 3x/minute, even a slight negative distension of the tent's walls signifies that air is moving through your tent's intake vents is going into your tent instead of out, and that odor - and heat - will NOT be exiting via the intake vents.

Many folks would add in a degree of overkill, since odor control is important. I guess I would agree with that .

In case it has not already been mentioned in this thread, adding a UPS (uninterpretable power supply) device to one's exhaust fan seems like a common sense thing to do. On average, fans don't consume an extreme amount of electricity, so a UPS that is properly sized for it shouldn't be all that expensive (the poor person in me yells, "But that's a relative statement," lol) - and certainly cheaper than a lawyer's services.

 

[TheFertilizer]

I would think any visible sign would denote a negative pressure. Err... You can have the stinkiest bowel movement in the history of the universe and, if the window is open with a fan sitting in it blowing out, you probably won't be vomiting from the smell whilst standing in the hallway outside the bathroom afterwards, because air is moving past you into the bathroom.

Okay, it's not quite that simple. But as long as your exhaust fan is moving enough fresh air through your tent to exchange the air 3x/minute, even a slight negative distension of the tent's walls signifies that air is moving through your tent's intake vents is going into your tent instead of out, and that odor - and heat - will NOT be exiting via the intake vents.

Many folks would add in a degree of overkill, since odor control is important. I guess I would agree with that .

In case it has not already been mentioned in this thread, adding a UPS (uninterpretable power supply) device to one's exhaust fan seems like a common sense thing to do. On average, fans don't consume an extreme amount of electricity, so a UPS that is properly sized for it shouldn't be all that expensive (the poor person in me yells, "But that's a relative statement," lol) - and certainly cheaper than a lawyer's services.

I think I misinterpreted what you meant, I thought you meant if they were being sucked in too much that was a bad thing.

Man if I never bought a UPS to protect my hundreds of gigabytes of porn I ain't going to do it to keep my neighbors from smelling my flowers But it's different when you're legal, my main reason for wanting a filter is that some people are just nosy and complain about the smell, and you don't necessarily want to make yourself a target for robbery either.

Good idea to prevent light disruption though!

 

[Gorgar]

Okay, it's not quite that simple. But as long as your exhaust fan is moving enough fresh air through your tent to exchange the air 3x/minute, even a slight negative distension of the tent's walls signifies that air is moving through your tent's intake vents is going into your tent instead of out, and that odor - and heat - will NOT be exiting via the intake vents.

Many folks would add in a degree of overkill, since odor control is important. I guess I would agree with that .

Ha ha, I love these discussions about properly ventilating a tent. I don't think enough people take this into account when putting a grow tent together.

I neither agree nor disagree with the 3X air exchanges per minute and I've seen that number (and more) mentioned before and I've also seen a low turnover rate of 1x in 3 minutes. But I do agree that it is a good idea to max out at 3 or more per minute and throttle things down. It seems to me that the negative pressure is more important than how negative the pressure is.

I've got a 330 CFM (rated) fan hooked up to a Variac (had to) and it's probably throttled back to around half of that for a tent that is around 100 CF. It's nice to have the extra headroom if needed, but the biggest advantage to running it slower, although probably a little less efficient, is the reduced fan noise.

 

[TheFertilizer]

Ha ha, I love these discussions about properly ventilating a tent. I don't think enough people take this into account when putting a grow tent together.

I neither agree nor disagree with the 3X air exchanges per minute and I've seen that number (and more) mentioned before and I've also seen a low turnover rate of 1x in 3 minutes. But I do agree that it is a good idea to max out at 3 or more per minute and throttle things down. It seems to me that the negative pressure is more important than how negative the pressure is.

I've got a 330 CFM (rated) fan hooked up to a Variac (had to) and it's probably throttled back to around half of that for a tent that is around 100 CF. It's nice to have the extra headroom if needed, but the biggest advantage to running it slower, although probably a little less efficient, is the reduced fan noise.

I have found it gets hard to avoid low humidity with the fan at max output as well. Usually never an issue though, but one reason why a person might want to turn it down.

 

[Gorgar]

I have found it gets hard to avoid low humidity with the fan at max output as well. Usually never an issue though, but one reason why a person might want to turn it down.

Yea, when it's winter here the humidity is pretty low and I have to add a humidifier during veg. Even running the fan low dumped the added moisture out of the tent, so I put the fan on a short cycle timer. It bounced the humidity up and down a bit doing this, but it pretty much evened it out and worked.

 

[Croatsan]

I have found it gets hard to avoid low humidity with the fan at max output as well. Usually never an issue though, but one reason why a person might want to turn it down.

Nothing a few wet towels won't fix