Debating Grow Tent Size & If I should go CFM Overkill

[McStrats]

I went overkill because it cannot stink. There's zero option for smell. A 6" would work fine but I'd have to run it faster then half speed. A 4" would be too small on full blast.

Going overkill on CFM is counter-productive in that the carbon needs lower CFM to be effective. Less = more.

 

[OldMedUser]

I can't speak from personal experience as my grow room is in an underground concrete bunker basically where it never gets over 65F in the summer and gets down to near freezing in the winter. I need my HID lights to keep the room warm enough so the heater isn't running while the lights are on wasting power on something that doesn't grow the plants.

I've often seen guys with 4x4 tents having heat issues even with LEDs when they use a 4" fan and scrubber and have to upgrade to 6" leaving a 4" fan and scrubber to collect dust somewhere.

Try searching the forums for heat issues and maybe read a few other threads about it to help you decide.

If you are getting a complete kit with tent, light fan etc online then overall price might make you pick one or the other. Mine is all a piece here and a piece there with a lot of DIY tossed in for good measure over the last 16 years. The only major new piece of grow equipment I've bought in all that time is the 6' Light Rail I got in Aug last year. Glad I did. Also got a TrimPro Unplugged and glad I did that too.

Choose wisely grasshopper.

 

[McStrats]

Do you guys think I should go with the 4" 190cfm fan for a 39x39x78 tent? It is much cheaper getting a 4" fan and filter, which is desirable, but I thought I could work the fan less by having a 6" and having it turned down low, instead of having a 4" turned at high 24/7.

It seems like the 4" would be plenty efficient for this size tent...I just don't want to underwhelm things. I'd rather buy right the first time and do everything proper from the beginning, that's why i was leaning towards the 6".

Again, I'm using led's, so heat from the lamps shouldn't be much of an issue. I will have a carbon filter attached

A 4" wide open will give you 165 ach which is beyond overkill. It will also render activated carbon useless as it needs "dwell time". Get a fan speed controller with the 4" motor/fan and run it on the low setting. Hold a sheet of printer paper at the exhaust. If you see a slight ripple you more than likely have enough ach.

 

[McStrats]

I've often seen guys with 4x4 tents having heat issues even with LEDs when they use a 4" fan and scrubber and have to upgrade to 6" leaving a 4" fan and scrubber to collect dust somewhere.

An exhaust fan doesn't really help all that much with heat. It will to a point but thats not what it is there for.

 

[SouthCross]

Going overkill on CFM is counter-productive in that the carbon needs lower CFM to be effective. Less = more.

Yes Sir, However, the filter is within manufacturer specifications. Lowest speed with corresponding 8" carbon. With a 6", the fan speed would pushing more air through a 6" filter. Scenario as you described and would be worse with a 4".

I also have a back up 6" filter with a 6" Vortex blower. Just in case...

 

[OldMedUser]

Going overkill on CFM is counter-productive in that the carbon needs lower CFM to be effective. Less = more.

That depends on the filter too. Many cheap ones use lower grade carbon that is less than half as effective as something like Australian carbon like used in Phresh filters. The cheap ones are what you get in those kits unless otherwise stated. The cheaper ones also use a thinner layer of carbon that's only about an inch thick and that has a lot to do with how well it removes odors.

An exhaust fan doesn't really help all that much with heat. It will to a point but thats not what it is there for.

How do you figure that? If the air you are pulling in is cooler than the air in the tent it damn sure helps with the heat. Heat and humidity control along with bringing in fresh air to replenish the CO2 are the exhaust fan's job.

Fans rarely move as much air as they are rated for. The rating is made with the bare fan blowing air without tubing or filter attached. The CFM drops off dramatically with real world use and your confusing calculations aren't taking that into account.

 

[McStrats]

That depends on the filter too. Many cheap ones use lower grade carbon that is less than half as effective as something like Australian carbon like used in Phresh filters. The cheap ones are what you get in those kits unless otherwise stated. The cheaper ones also use a thinner layer of carbon that's only about an inch thick and that has a lot to do with how well it removes odors.



How do you figure that? If the air you are pulling in is cooler than the air in the tent it damn sure helps with the heat. Heat and humidity control along with bringing in fresh air to replenish the CO2 are the exhaust fan's job.

Fans rarely move as much air as they are rated for. The rating is made with the bare fan blowing air without tubing or filter attached. The CFM drops off dramatically with real world use and your confusing calculations aren't taking that into account.

If the temps outside the tent are cooler then you will see a drop inside when you exhange air. If outside and inside are equal it won't change temps all that much.

 

[McStrats]

The CFM drops off dramatically with real world use and your confusing calculations aren't taking that into account.

The calculations are based on real world use..where else do you think they come from?

 

[McStrats]

That depends on the filter too. Many cheap ones use lower grade carbon that is less than half as effective as something like Australian carbon like used in Phresh filters. The cheap ones are what you get in those kits unless otherwise stated.

I am not familiar with Phresh. I use various kinds of activated carbon for plastic extrusion exhaust systems (stinky) and other industrial applications. Virgin coconut is one you can source from General Carbon...or Grainger if GC won't sell to you. It is very good for cannabis. The cheap inline carbon cannisters on amazon are adequate but you could make your own in about 20 mins and it would be far far better. There are several good tutorials online showing how.

 

[MonkeyPickAss]

If the temps outside the tent are cooler then you will see a drop inside when you exhange air. If outside and inside are equal it won't change temps all that much.

Laws of physics dictate that it would be impossible for the temps inside the tent to be the same as the temps outside. Of course the point of a fan is to remove heat that is literally it's job.

 

[McStrats]

Use a 4" fan and build a carbon filter and fill it with cocnut shell carbon.

 

[McStrats]

Laws of physics dictate that it would be impossible for the temps inside the tent to be the same as the temps outside.

No one is disputing this.

Of course the point of a fan is to remove heat that is literally it's job.

Not entirely. If your temp inside the tent is 98F there isn't a fan out there that will drop it to 85F. The primary job of the fan is to exchange fresh air.

 

[MonkeyPickAss]

No one is disputing this.



Not entirely. If your temp inside the tent is 98F there isn't a fan out there that will drop it to 85F. The primary job of the fan is to exchange fresh air.

What is the ambient temp in this hypothetical of yours? I feel like you are lacking some understanding of how this all works here.

 

[McStrats]

What is the ambient temp in this hypothetical of yours? I feel like you are lacking some understanding of how this all works here.

Silly.

 

[MonkeyPickAss]

Silly.

Gotcha! Makes much more sense now.

 

[OldMedUser]

If the temps outside the tent are cooler then you will see a drop inside when you exhange air. If outside and inside are equal it won't change temps all that much.

No Duh.

The calculations are based on real world use..where else do you think they come from?

I had just glanced at your calcs but looking them over now I see you aren't basing them on real world values but just the fans rated CFM and the space it's working in. If that fan is hooked up to a filter and say 10 feet of hose that has about 4 - 90 degree bends in it like with most installations and who knows how much hose on the outside of the tent to the actual exhaust point the CFM could be a 1/4 of it's rated output. I took a course in physical chemistry while getting my chem diploma and we had to factor in everything to be able to calculate what size pump or fan would be needed to do various jobs. The rough inner surface of flexible hose creates a lot of turbulence that causes a lot of air resistance too so the longer the hose the less the output.

The only way your calculations can be close to correct is if the fan is mounted without any hose on either side and if it's slightly sucking in the walls of the tent that means there is some resistance and the output goes down right there. Most people just have the fan plugged into their light timer with no other control at all and if the fan goes off in the dark then the RH goes way up until the lights come on again and the fan does too.

If you use a temp/RH controller, (like anyone interested in a stable environment for their plants should), the fan only comes on when ever the heat or RH reaches the set point to switch it on and then goes off once the temp or RH drops below that. In my grow room with a 1000W light like now the 6" fan at half speed comes on about every 20 min and runs for around 4 or 5. With a 4" fan it would be running full speed full time. I had 4" prior to getting the 6" so I do have experience with the difference it made in my room. With just 2 - 400W lights going it could barely keep up with the heat in the summer but I was getting some of the air from outdoors. Now all the air entering the room comes from the rest of the basement through filtered vents and is a lot cooler in the summer as previously stated in a past post.

I'm not using carbon for odor control. I have an ozone generator at the far end of 25' of 6" flex hose and it works better than the plugged up filter I got from my buddy. He used to run it at the end of his exhaust so the air was going into the middle of the can and exiting through the walls and dust cover. He lives in a dusty area with trucks going by his front door on a gravel road so all that dust is inside the filter rendering it useless. At full speed my wife could suck better than what my 400CFM fan could. Heat was going thru the roof using it as it wasn't moving much air. Now at half speed everyone is comfortable and my wife can use her sucking skills elsewhere.

 

[McStrats]

No Duh.



I had just glanced at your calcs but looking them over now I see you aren't basing them on real world values but just the fans rated CFM and the space it's working in. If that fan is hooked up to a filter and say 10 feet of hose that has about 4 - 90 degree bends in it like with most installations and who knows how much hose on the outside of the tent to the actual exhaust point the CFM could be a 1/4 of it's rated output. I took a course in physical chemistry while getting my chem diploma and we had to factor in everything to be able to calculate what size pump or fan would be needed to do various jobs. The rough inner surface of flexible hose creates a lot of turbulence that causes a lot of air resistance too so the longer the hose the less the output.

The only way your calculations can be close to correct is if the fan is mounted without any hose on either side and if it's slightly sucking in the walls of the tent that means there is some resistance and the output goes down right there. Most people just have the fan plugged into their light timer with no other control at all and if the fan goes off in the dark then the RH goes way up until the lights come on again and the fan does too.

If you use a temp/RH controller, (like anyone interested in a stable environment for their plants should), the fan only comes on when ever the heat or RH reaches the set point to switch it on and then goes off once the temp or RH drops below that. In my grow room with a 1000W light like now the 6" fan at half speed comes on about every 20 min and runs for around 4 or 5. With a 4" fan it would be running full speed full time. I had 4" prior to getting the 6" so I do have experience with the difference it made in my room. With just 2 - 400W lights going it could barely keep up with the heat in the summer but I was getting some of the air from outdoors. Now all the air entering the room comes from the rest of the basement through filtered vents and is a lot cooler in the summer as previously stated in a past post.

I'm not using carbon for odor control. I have an ozone generator at the far end of 25' of 6" flex hose and it works better than the plugged up filter I got from my buddy. He used to run it at the end of his exhaust so the air was going into the middle of the can and exiting through the walls and dust cover. He lives in a dusty area with trucks going by his front door on a gravel road so all that dust is inside the filter rendering it useless. At full speed my wife could suck better than what my 400CFM fan could. Heat was going thru the roof using it as it wasn't moving much air. Now at half speed everyone is comfortable and my wife can use her sucking skills elsewhere.

Anyone who runs dust into carbon without a media filter in front...and then gives up and uses an ozone generator instead...simply doesn't know what they are talking about. I am an engineer with 30 yrs experience with cfm, scfm, acfm...static pressure...blower curves, losses, etc...but none of that means a fricking thing here though. We live in an anti-knowlege age. All of what I said is verifiable...but f**k it...your stoner science wins out I guess...as you were..

 

[OldMedUser]

It was my buddy who ran the filter that way because he didn't know not to without filtering the air going in. I wasn't aware of the problem until I used the filter for the first time recently. I'll need to add more hose to give the ozone longer contact time with the aromatic molecules so it works better but there's barely a whiff of pot outside now as it is. I live out in farmland so odor control isn't that much of a priority but people do drop by to buy eggs and I'd rather they not get the full stink when they step out of their vehicles.

I have credentials as well and over well over 30 years working in various industries like hazardous waste disposal, stack testing at pulp mills, concrete plants and the like. Also grew my first buds in 1978 so have a bit of experience there too.

Your first calculations were useless in the real world and if you apply that kind of logic to your engineering it's no wonder you try to lord your "superior" knowledge over people you think use "stoner science" to figure things out.

I'd wager you'd be laughed off an engineering forum. Already happening here.

 

[AliCakes]

I see a tent with good reviews, dimensions 39x39x78. That would be much better.

I'll have to figure out if 2 - 300 watt led lights would fill that size tent properly. I can fill some cfl's in there temporarily if I have to.

That would be a much better tent choice. Once you strap in a filter and a fan at the top, then add in lighting and plants, you will be shocked how fast that head space fills up. I am currently researching leds to replace my hps as well. The only thing I have to say there is you can't judge an led fixture by it's wattage. Efficiency is changing so fast, that the term doesn't work well to describe the fixtures and many of the companies label the fixtures with "LED watts" not actual power. the term is an arbitrary number that the company uses to try and compare their fixtures to HPS.....for the most part the number is BS.

Best bet on lighting would be to go to the LED section here on rollitup. You will find many knowledgeable people that can help you with your choices.....just give them as exact of info as you can on the lights. They will be more than capable of helping.

 

[BadlyDrawnBoy]

Thanks for the info everyone. I'm pretty convinced now on getting the 6" fan, as well as the 39x39x78 tent. I definitely won't go any smaller in tent size, if anything I'll go up a bit. 6.5 feet should be fine though, and I'm not looking to grow more than 2 plants at a time, so 3x3 should be fine. My only concern with going up even higher in tent size is that I'll need more lighting to fill the tent. I'm already pushing pretty far past what I had originally wanted/expected to spend to get started. It's fine though, 6month financing ftw

That would be a much better tent choice. Once you strap in a filter and a fan at the top, then add in lighting and plants, you will be shocked how fast that head space fills up. I am currently researching leds to replace my hps as well. The only thing I have to say there is you can't judge an led fixture by it's wattage. Efficiency is changing so fast, that the term doesn't work well to describe the fixtures and many of the companies label the fixtures with "LED watts" not actual power. the term is an arbitrary number that the company uses to try and compare their fixtures to HPS.....for the most part the number is BS.

Best bet on lighting would be to go to the LED section here on rollitup. You will find many knowledgeable people that can help you with your choices.....just give them as exact of info as you can on the lights. They will be more than capable of helping.

I'm going into the LED sub forum right now to read. Thanks