Venting placement question

I'm trying to figure out the best way to vent my tent.

I have a 440CFM inline fan

Air cool hood (for a 400w CMH)

And I'm getting a 6" carbon filter here in the next week


A few years ago when I grew I set up my vent duct as:

Carbon filter - air cooled hood - inline fan - vented out window (fan had to push through only 4/5 feet of duct)


But now I'm reading that it is more ideal to blow air through the cool hood instead of suck air through it.. and I see a lot of people in pictures on this forum hook up the inline fan straight to the carbon filter.

My concern is that this time around the vented air will have to travel through two 45 degree bends (possibly only one) due to how I would have to hang the filter, and 10 feet of duct to make it out of the window if I run it before the air cooled hood.

Is this going to be efficient enough? Am I better off setting it up after the hood?
(I do have a speed controller as well) I'm just concerned about the air having to travel so far through the duct, If it's going to be an ideal set up.


I also have one of those smaller 200ish CFM inline fans that I could run halfway down the duct but I really don't want to have to use two fans just to vent the tent.

Thanks every one

I would open remove the glass from the air cooled hood, they are a joke. Put your filter at the top of the tent and run a 2-3' duct to the fan, a 400cfm fan should take care of the heat of a 400w in a tent just by renoving the hot air. And point a good fan directly at the light and keep it 12" away. If you have a small extra duct fan, you can connect that directly to the hood to blow air over the bulb.

So run

Filter - fan - light - window?

TheSkyway said:

So run

Filter - fan - light - window?

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Cool name. Skyway is a road nearby where i live.

I always attach fan to filter with self-tapping screws and finish off with some foil tape. Hang that contraption as high as you can. Duct that exhaust either through your aircooled hood and out of tent/room or take out glass and duct directly out of tent/room. 2nd option being best if temps allow.

glass filtlers out all the uvb

I would just run bare bulb with a cmh and use the fan as part of a stand alone exhaust system.

I'm a little fearful of what my temps would be like if I don't run it through the hood, but I guess if the fan is still venting out the heat that rises I might be okay. I didn't know the glass caused that much of a deficiency to the bulb, That is very good information to have

I doubt you're going to have any problem cooling a 400w with a 440cfm fan, even with a few bends.

People set them up both ways based on their concerns or beliefs. I think this covers the reasoning behind fan placement in the exhaust chain:

Pushing air is less efficient than drawing it, but...

I might even throw in my own thoughts and say it's possible that pushing the air would be a little quieter because the intake is covered by the scrubber (acting as a muffler), and the exhaust has to go through a sealed hood. If there is any reduction in noise, it's probably not much.

So, if you don't have to worry about whether or not you have enough cfm for your light, which I don't think you do, then you can probably place it where you want.

That's just my opinion tho

Blue brother said:

I would just run bare bulb with a cmh and use the fan as part of a stand alone exhaust system.

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I'm surprised at the number of people who use a sealed hood without it's intended purpose, which is to isolate the air from the grow space. There aren't any other reasons that I can think of for having a sealed hood.

JSB99 said:

I'm surprised at the number of people who use a sealed hood without it's intended purpose, which is to isolate the air from the grow space. There aren't any other reasons that I can think of for having a sealed hood.

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yeah me too, it's crazy cos when the grow air and coolant air aren't independent it makes it pretty much impossible to control all the parameters' that air cooled hoods are designed for.

Even with a fan speed controller, the room is too cold so the fan slows down, which reduces the amount of radiant heat being removed from the lamp which in turn burns the plants unless you raise the lights.

it's one of those topics I'm sick of schooling people on so I only tell newbies, if you've been doing this a while and your still doing this then Il leave you to it, if you're a newbie asking about air cooled lights then Il enlighten y'all lol

Blue brother said:

yeah me too, it's crazy cos when the grow air and coolant air aren't independent it makes it pretty much impossible to control all the parameters' that air cooled hoods are designed for.

Even with a fan speed controller, the room is too cold so the fan slows down, which reduces the amount of radiant heat being removed from the lamp which in turn burns the plants unless you raise the lights.

it's one of those topics I'm sick of schooling people on so I only tell newbies, if you've been doing this a while and your still doing this then Il leave you to it, if you're a newbie asking about air cooled lights then Il enlighten y'all lol

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I hear ya.

Noobs could save some money and put it towards something else in the grow, by going with an open hood.

Blue brother said:

yeah me too, it's crazy cos when the grow air and coolant air aren't independent it makes it pretty much impossible to control all the parameters' that air cooled hoods are designed for.

Even with a fan speed controller, the room is too cold so the fan slows down, which reduces the amount of radiant heat being removed from the lamp which in turn burns the plants unless you raise the lights.

it's one of those topics I'm sick of schooling people on so I only tell newbies, if you've been doing this a while and your still doing this then Il leave you to it, if you're a newbie asking about air cooled lights then Il enlighten y'all lol

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What do you usually do when the separate source air to aircool hoods is freezing? Lol. Usually gonna end up raining on the plants.

The day we finally had both: decent air coolable hoods AND charcoal filters, I was strictly building growrooms with separate air cooling the lights and charcoal filter exhausting straight out. Well, that got old and I realized i can usually get away with running my charcoal filtered exhaust through the hoods. Easier!
And i've been doing this a while lol

I don't aircool shit anymore. All my bloom rooms have DE's in them now

Aeroknow said:

What do you usually do when the separate source air to aircool hoods is freezing?

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Hmmmmm...that'd be an interesting test. Did this ever happen? I know cooler air is supposed to extend the bulb's life, but I wonder if the air can be too cold. Bet the flexible ducts would be freezing the room unless they were insulated.

JSB99 said:

Hmmmmm...that'd be an interesting test. Did this ever happen? I know cooler air is supposed to extend the bulb's life, but I wonder if the air can be too cold. Bet the flexible ducts would be freezing the room unless they were insulated.

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I've had a sealed growroom with air cooled lights where it was stressful during the winter time up here where I live now when it is snow cold outside. Starting with the inline, then the first few air cooled hoods, it would put out some serious condensate. Like it was raining for a minute lol. That's with humidity in the room around 50%, might not happen if below 40%, but it sucked.
I always use insulated flex ducting.
Better off taking out the glass and not air cooling during those cold months IMO.
But ducting the exhaust(non-sealed growroom of course) through the hoods works, it does. Might not always be the most ideal, but can definitely be practical sometimes. Plus, you never need to clean the inside of the glass that way

Aeroknow said:

I've had a sealed growroom with air cooled lights where it was stressful during the winter time up here where I live now when it is snow cold outside. Starting with the inline, then the first few air cooled hoods, it would put out some serious condensate. Like it was raining for a minute lol. That's with humidity in the room around 50%, might not happen if below 40%, but it sucked.
I always use insulated flex ducting.
Better off taking out the glass and not air cooling during those cold months IMO.
But ducting the exhaust(non-sealed growroom of course) through the hoods works, it does. Might not always be the most ideal, but can definitely be practical sometimes. Plus, you never need to clean the inside of the glass that way

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Condensation dripped from the bulb? I bet that was an uneasy sight!

JSB99 said:

Condensation dripped from the bulb? I bet that was an uneasy sight!

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Dripped from the glass. I would imagine the bulb would blow up if it was dripping wet lol

Aeroknow said:

Dripped from the glass. I would imagine the bulb would blow up if it was dripping wet lol

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Yeah, I always feared that. I'm sure you've heard of horror stories of bulbs blowing up in a grow and shattering glass everywhere. I always thought those water-cooled HPS bulbs were a cool concept, but I'd always be in fear of a leak which would surely not end well. Also like the Ice Box, but I imagine they've got to drip constantly. They're still around, but I haven't heard too many stories about their performance.

Aeroknow said:

What do you usually do when the separate source air to aircool hoods is freezing? Lol. Usually gonna end up raining on the plants.

The day we finally had both: decent air coolable hoods AND charcoal filters, I was strictly building growrooms with separate air cooling the lights and charcoal filter exhausting straight out. Well, that got old and I realized i can usually get away with running my charcoal filtered exhaust through the hoods. Easier!
And i've been doing this a while lol

I don't aircool shit anymore. All my bloom rooms have DE's in them now

Click to expand...

for me the air comes from a lung room but I can see your point, I'd probably source the air from a room and not directly outside

yeah de 400v is my next step, my space is expanding and I just cba with the fuck on of cutting extra holes running extra ducts etc.

I had thought of getting an infra red plant camera from dimlux and using it as a sensor for a fan speed controller rigged to the aircooling fan, to slow and accelerate the fan to keep the leaf surface temp at optimum. Then I thought.... Fuck that, 400v de lighting delivers the lumens that cooltubes afford and at a height where radiant heat isnt a problem. More efficient technology beats improved inneficient technology.

Blue brother said:

for me the air comes from a lung room but I can see your point, I'd probably source the air from a room and not directly outside

yeah de 400v is my next step, my space is expanding and I just cba with the fuck on of cutting extra holes running extra ducts etc.

I had thought of getting an infra red plant camera from dimlux and using it as a sensor for a fan speed controller rigged to the aircooling fan, to slow and accelerate the fan to keep the leaf surface temp at optimum. Then I thought.... Fuck that, 400v de lighting delivers the lumens that cooltubes afford and at a height where radiant heat isnt a problem. More efficient technology beats improved inneficient technology.

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When I switched out all my old air cooled 1000w SE's with DE's, it was a wash for the cooling needs. That's because I'm rockin 1/3 less fixtures now. It's the same amount of AC I was using before in these sealed growrooms. Fucking love these DE's!

Currently upgrading all of my 600w SE's I use for veg with 315w cmh's. Technology is bad ass.

Blue brother said:

I'd probably source the air from a room and not directly outside

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Sometimes that's just not doable.

Aeroknow said:

When I switched out all my old air cooled 1000w SE's with DE's, it was a wash for the cooling needs. That's because I'm rockin 1/3 less fixtures now. It's the same amount of AC I was using before in these sealed growrooms. Fucking love these DE's!

Currently upgrading all of my 600w SE's I use for veg with 315w cmh's. Technology is bad ass.

Sometimes that's just not doable.

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true, in which case id just run bare bulb and remove the radiant heat from the canopy by blowing air up through it or by blowing air over the bulb, I saw a thread a while back where some dude retrofitted ducting elbows and muffin fans to the end of each reflector, it just blows the hot air straight up to the ceiling where it's extracted.

it's below 0 here right now though and condensation isnt a problem, although I do understand that given the right conditions it could be a major problem.

I can't wait to get myself enough head room to go de400v, right now its just not feasible with the strains I'm running and my vertical space.

one of my reasons for using independently cooled lights was to allow my humidity to remain optimal, doing away with the need for so much air exchange meant my dehumidifier and humidifier could work more efficiently instead of one constantly running both can switch on and off when needed (which isn't nearly as often as before).