Single hole intake/exhaust help

Hey what’s up folks,
I am building a 24x30 garage, the wife kicked my grow tents out of the house, so I am setting up in the garage with vengeance!
I will set up a 4x4 in the back corner. I have the framing and OSB up now and I want to put a vent in now and build around it properly.
I’m looking for a 6 inch venting solution. I CANT HAVE THE SMELL MAKING ITS WAY INTO OUR PARKED VEHICLES! I will have a carbon filter,
I ONLY WANT TO CUT ONE 6inch HOLE.
My best idea is to put some 4inch ducting inside a 6inch ducting. And have one of them be the in and one the exhaust. This is kind of like ‘direct venting’ for natural gas fireplaces. One hole for both intake and exhaust.

what do y’all think? anyone do this?

i have a 6 inch and a 4 inch AC infinity fans.
I will get a filter to remove the smell,
How should I hook this up ? Blowing. Sucking. Which holes..

Sounds good if they’re timed and don’t work against each other also a forced air furnace doesn’t pull fresh air from its flute gas pipe

Howdy amigo, if your garage has a ceiling, why not vent the exhaust through a filter and into the attic. A good filter will cover most strains rather well. Good luck

Using a 4 inch inside a 6 inch is going to drastically reduce your extraction capability.
It will also suck back the same air your extracting unless I've misunderstood what you mean.

If all you going to do is have one 6" extractor then you won't need an intake , assuming your garage us not air tight. If it is then put some air bricks in or some roof vents.

Personally I'd extract with one fan and use the other for a scrubber only .

What you are thinking of is called concentric venting
I know that Panasonic makes a concentric hood for two 4" going to one 5" though for their baby erv
I don't understand why you need to pull intake from outside though. Typically garages will have enough air leakage just thru the garage door and whatnot. I would just set up the single exhaust and carbon filter without anything going outside first. Buy a co2 meter and see how humidity and temp conditions stay. After you are sure you need to bring air outside, I would consider adding a hood

Rozgreenburn said:

Howdy amigo, if your garage has a ceiling, why not vent the exhaust through a filter and into the attic. A good filter will cover most strains rather well. Good luck

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This is something you have to be careful with. If the attic is cold in the winter and hot humid growroom air is vented into it, you can create a huge mold issue
He might run into this issue in the winter in the garage , and heating the tent may be big issue

Nizza said:

This is something you have to be careful with. If the attic is cold in the winter and hot humid growroom air is vented into it, you can create a huge mold issue
He might run into this issue in the winter in the garage , and heating the tent may be big issue

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It is a possibility. I've done it before for a 2 year time frame with no issues. I did keep a dehumidifier in that garage and so my humidity was not much of an issue. I did have a well vented roof though. there can be a lot of variables.

Nizza said:

This is something you have to be careful with. If the attic is cold in the winter and hot humid growroom air is vented into it, you can create a huge mold issue
He might run into this issue in the winter in the garage , and heating the tent may be big issue

Click to expand...

I'd like to add to this.
We hear it often as advice , don't vent into an attic ect..
Now some may get away with it and others won't, depends on the ventilation I suppose.

But what I can attest to is the damage that can be done to a property when no ventilation and humid air is pumped into a space.
I'm currently replacing half my floors and joists and having to remove all internal plaster and take it back to brick because dry rot has set in badly and worked its way up the masonry feeding off the old lathe behind the plaster. I'm lucky it didn't make it to the roof because that would be another 25k to replace.

All this because someone vented into a subfloor space and sealed all ventilation.
Creating a perfect environment for dry rot mycelium.
Your insurance doesn't cover that by the way.

So when someone says dont vent into an attic , take heed because the financial cost to repair the potential damage is mind blowing .

I understand you only wanna make 1 hole.To have incoming & outgoing might need 2. I cut in 8 x 12 louvered vents into the gable/attic ext,boxed em in on inside,screwed a flange onto it & put a can filter ,passive on the incoming & same at other end with a can fan exhausting. My neighbors haven't a clue ! The cans & fan sit on the rafters so they're out of the way

I dry in my garage in a small 4x2 tent,vented out through the roof what was an old wood stove vent.

My dog door is cold air in.

Hey thanks guys for the good responses.
I won’t be venting into the attic, for many reasons, humidity, I put a metal roof, it just won’t be a good idea for me.

I think the reason I wanted I separate intake was so that I would not be sucking air into the garage from outside, cooling it down, and as well so I wouldn’t be sucking car exhaust fumes and other ‘garage’ fumes into the tents…
But now that I’m thinking about it, maybe I do not need worry about fumes… do I?
I think I will try just an exhaust ,6inch and a square louvred style vent. If I am not satisfied I will continue to think about a duct inside a duct.

The opening for return air should be 3 times your vent size.I think.
So 6",= R squared x 3.14 so about 28 sq inches for passive air in.
You'd need a pretty big pipe for your 6" vent to run through.

Different if you plan on running an inline for air in I guess.

SnidleyBluntash said:

Hey what’s up folks,
I am building a 24x30 garage, the wife kicked my grow tents out of the house, so I am setting up in the garage with vengeance!
I will set up a 4x4 in the back corner. I have the framing and OSB up now and I want to put a vent in now and build around it properly.
I’m looking for a 6 inch venting solution. I CANT HAVE THE SMELL MAKING ITS WAY INTO OUR PARKED VEHICLES! I will have a carbon filter,
I ONLY WANT TO CUT ONE 6inch HOLE.
My best idea is to put some 4inch ducting inside a 6inch ducting. And have one of them be the in and one the exhaust. This is kind of like ‘direct venting’ for natural gas fireplaces. One hole for both intake and exhaust.

what do y’all think? anyone do this?

i have a 6 inch and a 4 inch AC infinity fans.
I will get a filter to remove the smell,
How should I hook this up ? Blowing. Sucking. Which holes..

Click to expand...

How big is your actual grow space? Multiple tents/rooms?

SnidleyBluntash said:

Hey thanks guys for the good responses.
I won’t be venting into the attic, for many reasons, humidity, I put a metal roof, it just won’t be a good idea for me.

I think the reason I wanted I separate intake was so that I would not be sucking air into the garage from outside, cooling it down, and as well so I wouldn’t be sucking car exhaust fumes and other ‘garage’ fumes into the tents…
But now that I’m thinking about it, maybe I do not need worry about fumes… do I?
I think I will try just an exhaust ,6inch and a square louvred style vent. If I am not satisfied I will continue to think about a duct inside a duct.

Click to expand...

Its not worth trying to rig up a direct vent i have installed hundreds of DV heaters just cut 2 4in holes you dont want to be sucking in car exhaust. I have seen brand new garages rotted out after 1 winter from blowing warm humid air into the frozen attic space the warm air condenses an will just drip all winter.

^^^
cheapest solution right here ^^^
two four inch dryer vents with damper and a four inch galvanized wye
https://growace.com/products/6-x4-x4-y-duct-connector?variant=39714550022308&gclid=EAIaIQobChMIsK-4vvzm-QIVq21vBB1sUgG_EAQYBCABEgIG1_D_BwE
A little flex duct and viola

Panasonic FV-WC04VE1 WhisperComfort Dual Chamber | Build.com
or one of these as a combo intake and exhaust

be mindful, the wye is styrofoam and when installed you need clearance for it. there is no way to offset this off the hood, the Y goes straight in so if something is in the way ( you hug one side of a joist with the 5 1/4 or whatever hole) the wye won't go onto the hood correctly.

edit. I just found this Panasonic FV-EB04VE1 WhisperComfort™ Dual | Build.com so if you mess up or have a restriction you could offset it. pretty expensive though

Nizza said:

Panasonic FV-WC04VE1 WhisperComfort Dual Chamber | Build.com
or one of these as a combo intake and exhaust

be mindful, the wye is styrofoam and when installed you need clearance for it. there is no way to offset this off the hood, the Y goes straight in so if something is in the way ( you hug one side of a joist with the 5 1/4 or whatever hole) the wye won't go onto the hood correctly.

edit. I just found this Panasonic FV-EB04VE1 WhisperComfort™ Dual | Build.com so if you mess up or have a restriction you could offset it. pretty expensive though

Click to expand...

That dual chamber wall is exactly what I was looking for. Unfortunately I won’t be paying 70$ for it! But thanks, I will keep looking. Or maybe make one.


this is the kind of vent outlet I was imagining, if I had that half piece…

Is just one 4x4 tent, nothing major. I might set up a 2x4 as well but there is a plant count limit of 4 so…
But I can’t smell up the vehicles… the funk sticks to everything!! Thanks folks.
I think I’ll decide between 2 4inch holes, that would really make everything easier.
The pics are where it will go. A hole above.

Gas furnaces use a duct like you speak. So they can intake fresh air and exhaust combustion through the same boot. https://store.acpro.com/intertherm-saw27472a-roof-jack-for-gas-furnace-27-47-inches-41655

SnidleyBluntash said:

Hey what’s up folks,
I am building a 24x30 garage, the wife kicked my grow tents out of the house, so I am setting up in the garage with vengeance!
I will set up a 4x4 in the back corner. I have the framing and OSB up now and I want to put a vent in now and build around it properly.
I’m looking for a 6 inch venting solution. I CANT HAVE THE SMELL MAKING ITS WAY INTO OUR PARKED VEHICLES! I will have a carbon filter,
I ONLY WANT TO CUT ONE 6inch HOLE.
My best idea is to put some 4inch ducting inside a 6inch ducting. And have one of them be the in and one the exhaust. This is kind of like ‘direct venting’ for natural gas fireplaces. One hole for both intake and exhaust.

what do y’all think? anyone do this?

i have a 6 inch and a 4 inch AC infinity fans.
I will get a filter to remove the smell,
How should I hook this up ? Blowing. Sucking. Which holes..

Click to expand...

Sounds like allot of kneepad work! jk'ng. I'd vear from that plan. There are reasons we don't do that. Are all you setting up is a 4x4? No co2? Does your garage have ridge vents & soffit vents? Sorry, I didn't read everything,bout half. The most common technique I think, well at least it's how I do it. Is x2 vents. One is an Intake 6" off the floor, running through a small, cleanable filter box on one side with a 6" inline fan (for a room) & an exhaust on the ceiling going through a scrubber (Stapped to ceiling horizontally). The exhaust can go anywhere you want it because your environment should be controlled anyway. But, there's no better place to blow it then outside unless your heating your house in the winter. Big savings, using a 10x10 or more. The fans can be located anywhere for your convenience. Far from the scrubber, near the exit hole for example. A gable vent would look best there i think. Straight pipes and reduced bends & length will increase the efficiency output but no biggie. I'd kick on the De-Hu in the garage for a wk. prior, on the lowest setting, full time if you've never leached the cement yet. Of not a trench drain at the level walk out then maybe consider one if water flows in.
I never recommend drawing outside air unless your a big facility or greenhouse. Sometimes winter cooling is cool though. Air is cleaner if you have a cold climate area.
May I ask what gave you the idea to single port both? Sucking then blowing your scrubber will cause unwanted spores or whatever in the air too. Not to mention screw up the your grow envoirnment. Suck out of the scrubber high up where the hot, humid air is. Draw in at the same time from the flour'ish area as it's the coolest, driest spot. Your garage as a whole will be de-hu'd so your good there. A simple stand up, daul-port will do the job in the winter and a window ac in the summer.. Good luck grower! Try to avoid exesive positive or negative air pressure. With your intake fan dimmed or a few bends added, then the exhaust will create a minor negative air pressure effect which is good.