Two simple questions with a lot controversy

Hi Guys,

As the subject says, I have two questions that there are many different answers to across the different Growing forums. But I will approach this a bit differently, instead of asking about the technical explanations, technical theories etc etc, I will instead ask from the perspective, Does it actually work??

So to my first question.

1. For all of you who actually do, or have tried having the Carbon filter at the end of the ventilation system, so Pushing the air through the filter at the end, Does it work for you? Does it have any noticeable Cons? How well does it work? Have you tried both ways and can compare? Any noticeable change in the Cfm from 1 way to the other?


My second questions is regarding Cool tube and Inline fan.

2. The issue about small grow tents is of course space, in practicality having the fan and filter outside the tent would be optimum, but since there is such controversy about this also, I am wondering you people who use the inline fan AFTER the cool tube, how does it work for you? Have any of you had your fans die, and you suspect its due to the extra heat coming from the cool tube as some claim to be a reason for not having the fan after the cool tube? Have you tried both ways, fan before the cool tube and after ? How do they compare in terms of temperature, any difference?


I read so many different OPINIONS on this subject, so please refrain from writing unless you speak out of first hand EXPERIENCE or knowledge that you can refer to an authority ( fan och carbon filter company statements, actual real world tests).

Hey brother .... i had the same questions when i started. And went ahead with the fan AND filter beimg outside the tent and at the end of the cooltube. So. I used to have the cool tube sucking air from the tent and out the tent, through the inline fan (8" made by xplair) then (during flowering) through my carbon filter. And the tent will be cooled passively by having negative pressure in which sucked air passively from outside.
Later, i decided to cool the tube with air sucked from outside the tent (so fresh and cool air from outside) and another 8" fan sucking hot air from the tent and passively intaking air from oitside the tent from neg pressure. I did this and added the second fan as a back up in case thw first one breaks! Been 4 years and the fan is just fine. Now i went back to the original way (one fan suckin hot and humid air from the groom, through the tube then the fan then filter (fan and filter outside the groom) .... the second fan will be used as needed to actively force cool air in the groom when ever needed or as a back up for the first fan)
I havent done it the other way around to compare ... but doing it the way ive been doin for years was just fine. Is it the most efficient way? Probably not. But for my circumstances (small groom with huge fan and carbon filter) leaving them outside made more sense and no problems!
I hope this helps brother and happy growin

Check out my new Organic Fruit Garden:
https://www.rollitup.org/index.php?threads/930415/
and my previous QuadStrain grow :
https://www.rollitup.org/index.php?threads/916619/
and my previous TriStrain grow :
https://www.rollitup.org/index.php?threads/883569/

Hey DrCannaPath, Thanks for the answer and your input.
Let me see if I understood you correct. When you added the second fan at first, you had 2 exhaust from the tent?

1. air from outsude ==>Fan ==> cooltube ==>out from tent
2. Air inside tent == > Fan==> Filter

I feel this is kind of overkill in my case, 250hps, and I couldn't stand with the noise of 2 fans frankly , small apartment.

Why did you change from the initial configuration, having the fan and filter outside the tent and sucking air passively inside the tent? Was the temperature ok this way, do you have any ballpark numbers ambient temp to tent temp ?

Oneirogen said:

Hey DrCannaPath, Thanks for the answer and your input.
Let me see if I understood you correct. When you added the second fan at first, you had 2 exhaust from the tent?

1. air from outsude ==>Fan ==> cooltube ==>out from tent
2. Air inside tent == > Fan==> Filter

I feel this is kind of overkill in my case, 250hps, and I couldn't stand with the noise of 2 fans frankly , small apartment.

Why did you change from the initial configuration, having the fan and filter outside the tent and sucking air passively inside the tent? Was the temperature ok this way, do you have any ballpark numbers ambient temp to tent temp ?

Click to expand...

Oh i see. For a 250w thats an overkill for sure. I started with 600w MH/HPS and my set up was:

Hot and humid Air from the tent -> cooltube -> out of tent into fan -> carbon filter. It worked well and shoyld be plenty fine for yoir 250w hps (given you have a descent inline fan)

Later i added 350w LED cobs to the 600w in the tent (950w total) .... the heat went up just a little but i still wanted an optimum temp. So i changed it to:
1. air from outsude ==>Fan ==> cooltube ==>out from tent
2. Air inside tent == > Fan==> Filter
but now i changed my groom from a 4'x4' to a 5x4 with open end (so air is free flowing from the front to the back and out) so i switched it back to the old way

Check out my new Organic Fruit Garden:
https://www.rollitup.org/index.php?threads/930415/
and my previous QuadStrain grow :
https://www.rollitup.org/index.php?threads/916619/
and my previous TriStrain grow :
https://www.rollitup.org/index.php?threads/883569/

Cool, we are kind of in different leagues then in terms of power, 250<600 (950) .

I actually had a regular hood/reflector at first, I just got the whole kit a week or so ago, and I did a few our run with the tent empty and I had around 85-88F degrees at 12-13 inches from the lamp. I kind of got worried about the temps, not sure if it would be better or worse when there is 4 plants inside at 2-3 feet. So i contacted the shop I bought everything from, and essentially I got a real good deal, 20% off on the cooltube, plus free shipping and also I would get free return with the cool tube when it arrives. So i ended up paying just around 24$ extra for the cooltube. If it helps me 4-5 degrees Im happy with the results.

For now I have the "recommended" way inside the tent. If it proves to work well ill leave it. The only thing Im worried about is that the airflow will be insufficient due to loss of CFM because of all the bends and the ducting. My fan is running at full speed 280Cfm, will it suffice you think? This is also a diffuse subject that I have not really been able to find good information about, how much you actually loose due to bends and 3-4 feet of ducting. Some say 90degree bends restrict up to 60%, but it sounds just too much.

What power did your 8" fan have?

The main principles with ventilation is:
1. Make sure your fan, filter, and air volume are compatible with each other.
2. Keep ducting to a minimum, and with as little bends as possible. Rigid ducting is preferable but more costly and more complicated to install.

The rest has little to no impact if your system is built correctly.
Whether you are pushing or pulling air through the filter doesn't matter as long as your fan can handle the static pressure.

I've done both ways, pushing and pulling.currently I'm running 8" filter,6" ducting, light,ducting,light,ducting,fan, ducting exiting outside. I think pulling extracts the heat better.

toaster struedel said:

I've done both ways, pushing and pulling.currently I'm running 8" filter,6" ducting, light,ducting,light,ducting,fan, ducting exiting outside. I think pulling extracts the heat better.

Click to expand...

Love your logo bro and Go Steelers and Go Pens

Check out my new Organic Fruit Garden:
https://www.rollitup.org/index.php?threads/930415/
and my previous QuadStrain grow :
https://www.rollitup.org/index.php?threads/916619/
and my previous TriStrain grow :
https://www.rollitup.org/index.php?threads/883569/

To be honest beo i cant remember what CFM is my fan ... but i know its enough for that size groom (4x4 or even 5x4)

Check out my new Organic Fruit Garden:
https://www.rollitup.org/index.php?threads/930415/
and my previous QuadStrain grow :
https://www.rollitup.org/index.php?threads/916619/
and my previous TriStrain grow :
https://www.rollitup.org/index.php?threads/883569/

those fans are designed to be used in hvac systems, where the temps can rise well above whatever heat your light is going to put out, so thats not a valid concern.
i don't want to vent the hot air back into my house, i want that heat going outside (unless its the middle of the winter)
so i can't put the filter at the end of the line. they do work that way, but its hard to conceal a shiny can thats making a blowing sound. space may be an issue, but space against the roof of your tent? you have a very low tent to work in? i have plenty of room in an 80 inch high tent to hang the filter above the light and still have room to grow up to 5 foot tall plants

toaster struedel said:

I've done both ways, pushing and pulling.currently I'm running 8" filter,6" ducting, light,ducting,light,ducting,fan, ducting exiting outside. I think pulling extracts the heat better.

Click to expand...

You've done both ways you say, that qualifies you to answer the questions, but you really didnt answer any of them. Had any of your fans die on you ? How do they compare in terms of temperature, any difference?

Roger A. Shrubber said:

those fans are designed to be used in hvac systems, where the temps can rise well above whatever heat your light is going to put out, so thats not a valid concern.
i don't want to vent the hot air back into my house, i want that heat going outside (unless its the middle of the winter)
so i can't put the filter at the end of the line. they do work that way, but its hard to conceal a shiny can thats making a blowing sound. space may be an issue, but space against the roof of your tent? you have a very low tent to work in? i have plenty of room in an 80 inch high tent to hang the filter above the light and still have room to grow up to 5 foot tall plants

Click to expand...

I've seen it stated that the fans should operate between 20-30C, 68 - 86F. I have no idea what the temperature would be going through the fan, if the air in tent is, 25-26, how much does the lamp manage to heat the air going over it, and how much does it cool down on the way out through let say 2 feet of ducting, if I decided to put the fan outside?

I have room over the tent, thats no issue, but what did you had in mind, that I put the fan outside on the tent?

i can tell you that for a 4x4 x 6.5 foot tent, i went with a 400 cfm phresh filter hooked to a 440 cfm fan that i dialed down, it was NOT enough to control the odors of four plants in flower. i had to step up to the 500 cfm fan hooked to the same 440 fan running almost on full to control the odors. the 400 cfm was doing fine handling the heat from a 600 watt hps, but when the third plant went into flower, i started smelling it again, and when number 4 kicked in, it was obvious i needed a bigger filter. i've been running the same fan for 3 years and it seems as good as the day i bought it, you either get a good one that will last forever, or you get a crap one that won't, shouldn't take long to figure out which you have

Oneirogen said:

You've done both ways you say, that qualifies you to answer the questions, but you really didnt answer any of them. Had any of your fans die on you ? How do they compare in terms of temperature, any difference?

Click to expand...

I clearly said pulling extracts heat better, atleast in my situation. Sometimes in the winter I run no fan at all. If your fan dying kills your plants your lights are probably too close.

Roger A. Shrubber said:

i can tell you that for a 4x4 x 6.5 foot tent, i went with a 400 cfm phresh filter hooked to a 440 cfm fan that i dialed down, it was NOT enough to control the odors of four plants in flower. i had to step up to the 500 cfm fan hooked to the same 440 fan running almost on full to control the odors. the 400 cfm was doing fine handling the heat from a 600 watt hps, but when the third plant went into flower, i started smelling it again, and when number 4 kicked in, it was obvious i needed a bigger filter. i've been running the same fan for 3 years and it seems as good as the day i bought it, you either get a good one that will last forever, or you get a crap one that won't, shouldn't take long to figure out which you have

Click to expand...

Not sure if its me or you, but I dont understand, You had 1 fan with 440cfm dialed doww, and that wasnt enough for the odour, so you added another fan? Wouldnt this be less effective since the fans would be pulling the air too quickly through the filter?

On your comment about the quality of the fan "shouldn't take long to figure out which you have" , how so? How would I know, its not like there is an abundance of reviews and tests of inline and mixed-inline fans. And price alone doesnt say too much.

toaster struedel said:

I clearly said pulling extracts heat better, atleast in my situation. Sometimes in the winter I run no fan at all. If your fan dying kills your plants your lights are probably too close.

Click to expand...

Not mean to nitpick but for me there is a difference saying "I think pulling extracts the heat better" and later on saying as a matter of fact "I clearly said pulling extracts heat better" . But appreciate the input anyway

Oneirogen said:

I've seen it stated that the fans should operate between 20-30C, 68 - 86F. I have no idea what the temperature would be going through the fan, if the air in tent is, 25-26, how much does the lamp manage to heat the air going over it, and how much does it cool down on the way out through let say 2 feet of ducting, if I decided to put the fan outside?

I have room over the tent, thats no issue, but what did you had in mind, that I put the fan outside on the tent?

Click to expand...

people run 3 x 1000 hps on one large fan, your lights aren't going to produce enough heat to matter to your fan, i wouldn't even take that into consideration. its moot, you don't have the equipment that it would take to make the heat on your fan an issue.

Oneirogen said:

Not sure if its me or you, but I dont understand, You had 1 fan with 440cfm dialed doww, and that wasnt enough for the odour, so you added another fan? Wouldnt this be less effective since the fans would be pulling the air too quickly through the filter?

On your comment about the quality of the fan "shouldn't take long to figure out which you have" , how so? How would I know, its not like there is an abundance of reviews and tests of inline and mixed-inline fans. And price alone doesnt say too much.

Click to expand...

i didn't add another fan, i traded to a larger filter with the same fan.

Roger A. Shrubber said:

people run 3 x 1000 hps on one large fan, your lights aren't going to produce enough heat to matter to your fan, i wouldn't even take that into consideration. its moot, you don't have the equipment that it would take to make the heat on your fan an issue.

i didn't add another fan, i traded to a larger filter with the same fan.

Click to expand...

Alright, thanks, then the issue of heat ruining my fan is out of the way, I just might move everything outside the tent next grow, gives me another 8" of height, and next grow can perhaps be some nice sativas =)

If you have a dusty environment pushing the air into the can filter will plug it up inside. I got one here a buddy gave me and that's how they ran it. I hooked it up with my 6" and couldn't keep the temps below 82 or so at full speed and I had no problem keeping it 75 with it running 1/2 speed before. When I unhooked the duct on the out side of the fan there was bugger all air flow. My cheap little 6" duct fan would push more air by itself and my inline is 400cfm at least. Has no markings on it but blows better than a $100 hooker. Going: filter -> fan -> 1ft duct -> outside. Was running a 1000W HPS with an open batwing reflector in my 7x8x6.5h underground concrete bunker for a grow room.

Got the no-name fan off my buddy too and it's sounding like it might be on it's last legs. Just a grumble sometimes and a bit of vibration when you touch the housing. I have it suspended from the ceiling on a bungee cord so any vibration doesn't transmit thru the ceiling up here into my man cave. I'm literally sitting on my grow room.

Oneirogen said:

I did a few hour run with the tent empty and I had around 85-88F degrees at 12-13 inches from the lamp.

Click to expand...

Where was the thermometer when you took the readings? If its right under the light then your getting a false reading. It should be above the light line to measure air temps which are what you want to measure. The IR in the HPS heats up the thermometer very quickly. Plants can take a lot more radiant heat than they can high air temps.
If this is what you have done I would try another test run and would be surprised if you didn't see a drop of 5-10 degrees F