Does air coming into a room via fan, force air out of the room (and other questions)

[JSB99]

Hey everyone! I'm going to apologize in advanced for the long post. I just wanted to make sure I covered as many questions or comments in advance as possible.

I got pretty far setting up my new room, but I'm up in the air about using a 4" inline fan for the room's air exchange to either pull air in, or push air out of the room. I know pulling is more efficient, but with my setup, I think it might be negligible. I've also got some questions above some of the pics, if all you cool people out there can give some good advice.

My setup:

• 4x4 tent in a fairly sealed 10x10 room with central ac (For now. I'm getting a window ac for the room soon.)
• 600w mh/hps
• 2x4 closet w/air register from hallway for fresh air intake (closet will be used for mothers/clones)
• 6" air cooled hood (draws air from under the house and exhausts into attic w/insulated duct)
• 6" 440cfm for hood, 4" 190cfm for tent, 4" 190cfm fan for room air exchange (what I'm questioning)
• growing in coco

Looking at the pictures below, you can see the 6" air intake for the room in the closet, which is connected to a 6" x 14" register box. The room air exhaust will go from the ceiling, through the attic via insulated duct, and to a return register either in the hallway or into an unused room. I'd like to run it with a 15 minute incremental timer, but I wouldn't know if that would be sufficient until I tuned the room.

I think I have three options for the room air exchange:

• Connect the fan to the air intake in the closet, and create positive pressure to push air out to the room through vents on the door (not installed yet)
• Mount the fan towards the top and outside, of the closet, and exhaust it into the room without it being directly connected to the air intake at the bottom of the closet, or the air exhaust mounted in the ceiling. The fan would be connected via duct towards the top of the closet.
• Hang the fan from ceiling (like I've done in the pic below), and push the air to a register in the hallway or into the other room via insulated duct in the attic

What I'm wondering is, if I'm sucking air into the room, am I also pushing air out of the room by creating positive pressure, regardless of how I have it configured? I'd like to seal the closet, mount the fan above the closet door on the outside of the closet, connect the fan to the closet to draw air and create positive pressure, which would force air out of the ceiling duct. The room is almost silent with the bedroom door shut, even with the fans maxed out. I had the interior walls insulated when I had my house built, and it drastically isolates the sound. But a fan directly connected to a vent will surely cause some noise. I made a couple fan mufflers I can use if I have to be connected to a vent, so that might help.

It can't be seen, but I use pantyhose for a filter on this duct as well as the hood air intake. With the room as sealed as possible, fresh air will be forced to enter through this vent. The extra flexible duct is just for some light-proofing.

Hallway register on the other side of the closet...

I know that venting into the attic may cause problems with humidity, but that's when exhausting the humid air from the tent, not the hood, where the air is drawn in from under the house. Does anyone think that's still going to cause issues down the road?

I hate loose wires lol. I'll spend hours organizing and tying up cords!

Keeping my ballast cool...

I over-watered my Headband a bit, so she's a little droopy right now. Once she's grown a little I'll take four clones and grow them out.

Does anyone else keep their scrubber unhooked during veg? I think it'd be wasting electricity because of the extra draw needed.

My room exhaust fan waiting to be hooked up somewhere...

Temps hover in the 75 to 79 range, with the house set to 75 and the room door closed. I'm letting it get into the low 80's right now to try and dry my Headband out a bit faster. Humidity hovers between 45% and 55% with a wet towel wick.

Thx

 

[Final Phase]

From what I can see, you have done a nice clean job of setting the grow space. All I can say is air flow is extremely important. Keeping the air moving is a must
for healthy plants. It will also keep your chances of mold and mildew down. If you have to add more exhaust in order to move the hot air out soon as possible.
Good luck and hope to see you get a grow to the harvest line!

 

[JSB99]

Thanks!

I do have a good amount of circulation and the temps are balanced really well (about 4 degrees above the house temperature). My ac controller has a "circulation" mode which blows air from the handler for ten minutes then off for twenty. I'm wondering if that's providing enough pressure to push the old air out. If that's the case, and if my temps stay manageable, I may not even hook the extra fan up. Here in OR, we don't have too many hot months out of the year.

 

[mjinc]

Use the hanging exhaust with ducting to push it out into the attic, it should give you the most benefit. If you use the fan to bring in air and then use the vents in the door to exit you are not going to get as much benefit as hot air rises and so you will be pushing cooler air out the room.

 

[Grandpapy]

Looks good, keep tweaking!
From here I'd say to check your Ballast, it looks like it needs to be rotated to vent hot air up, it will run cooler.

 

[Roger A. Shrubber]

you have a 440 cfm fan exhausting into your attic already, that should set up a pretty good negative pressure situation right there.i wouldn't worry about running the other two fans at all, i have a 4x4 tent with a bare 600 hanging vertically in it and the highest it ever gets is 82. you don't really need that duct from the floor register, just leaving the bottom flaps open will pull in all the air needed.i got a 550 cfm filter, and a 440 cfm fan, run it wide open lights on, half speed lights out, have no temp problems

 

[Roger A. Shrubber]

if you run all that stuff into your house duct work, your whole house will reek when you start to flower, even with the exhaust going to the attic

 

[JSB99]

you have a 440 cfm fan exhausting into your attic already, that should set up a pretty good negative pressure situation right there.i wouldn't worry about running the other two fans at all, i have a 4x4 tent with a bare 600 hanging vertically in it and the highest it ever gets is 82. you don't really need that duct from the floor register, just leaving the bottom flaps open will pull in all the air needed.i got a 550 cfm filter, and a 440 cfm fan, run it wide open lights on, half speed lights out, have no temp problems

if you run all that stuff into your house duct work, your whole house will reek when you start to flower, even with the exhaust going to the attic

I think you may have missed how I have this configured. The hood is sealed properly, meaning that the air is totally separate from the grow. The 440 pulls air from under the house, through the hood, and into the attic. The 440 pulls no air from the room or house at all. It is dedicated to the hood.

The 190cfm fan is only to vent the tent. When I move to flower, I will connect the scrubber hanging in the tent.

The second 190cfm fan is only to refresh the air in the room. When I get a window ac, I will disconnect the house vent and seal it. The tent will then get it's air from the room, which wil be cooled with the window ac. Window air conditioners don't exchange air, so this is why I have the additional fan. I'm only using the room's vent until I get the window ac.

 

[JSB99]

Use the hanging exhaust with ducting to push it out into the attic, it should give you the most benefit. If you use the fan to bring in air and then use the vents in the door to exit you are not going to get as much benefit as hot air rises and so you will be pushing cooler air out the room.

Thanks! That definitely helps!

The fan to exchange the room air will actually be vented into another room and not the attic. It will go through the attic with insulated duct to the other room. The tent has a scrubber, so the room should be clear of odors. Also, the hood air is isolated, so the room shouldn't be getting all the much warmer than the rest of the house, if any. That's why I was thinking of exhausting the air into another room. I hate the thought of exhausting ac cooled air outside. I'm trying to make it as energy efficient as possible. It seems like a good concept, but I've yet to try it so I don't know if it'll work for sure.

I'm the only one in my house and all my neighbors either smoke, or are cool with it, so I'm not worried about odors. It's also legal here in Oregon. Still, I wouldn't think there'd be any odor with the scrubber.

 

[JSB99]

Looks good, keep tweaking!
From here I'd say to check your Ballast, it looks like it needs to be rotated to vent hot air up, it will run cooler.

Good idea!

Thx

 

[PKHydro]

Ok. So your not running a sealed tent with co2. So you need to have an exhaust and an intake. Your going to need a fan big enough (cfm) to hook up to your charcoal filter and exhaust that hot smelly air out of your tent and house. As for the intake...it can be passive if your exhaust fan is big enough.


I'm kind of confused as to how you've got it set up, but it almost seems like your backwards with a passive exhaust and a forced intake. Also by the sounds of it you had just planned to use that charcoal filter as an air scrubber...which would be fine in a sealed room, however with an intake and exhaust you need to hook that filter up in line with your exhaust otherwise everyone will smell your grow.

 

[JSB99]

Looks good, keep tweaking!
From here I'd say to check your Ballast, it looks like it needs to be rotated to vent hot air up, it will run cooler.

With the exhaust air blowing on it, it stays cold. I was questioning whether to exhaust the tent higher, towards the ceiling, but the air is cool so I'm not going to mess with it unless it becomes and issue.

This is my 4" tent exhaust fan.

 

[JSB99]

Ok. So your not running a sealed tent with co2. So you need to have an exhaust and an intake. Your going to need a fan big enough (cfm) to hook up to your charcoal filter and exhaust that hot smelly air out of your tent and house. As for the intake...it can be passive if your exhaust fan is big enough.


I'm kind of confused as to how you've got it set up, but it almost seems like your backwards with a passive exhaust and a forced intake. Also by the sounds of it you had just planned to use that charcoal filter as an air scrubber...which would be fine in a sealed room, however with an intake and exhaust you need to hook that filter up in line with your exhaust otherwise everyone will smell your grow.

Ok. So your not running a sealed tent with co2.

The tent is set up as if it's a sealed environment, but for a different intention. I do not plan to inject co2. It's set up like this specifically to control heat, without having to adjust things on a day to day basis.

So you need to have an exhaust and an intake

I'm using the microscreens at the bottom of the tent for passive intakes

Your going to need a fan big enough (cfm) to hook up to your charcoal filter and exhaust that hot smelly air out of your tent and house.

The 4", 190cfm inline fan sitting on top of the tent is my exhaust. I also have a 4" carbon scrubber. It's not hooked up right now because I am not flowering yet. I just started vegging. Since there are no odors, I see no reason to hook up a scrubber that will ultimately make my 4" fan work harder, get hotter, and probably lessen the life of the scrubber. When I start flowering, I will be hooking the scrubber up to the fan.


I've set up grow rooms before and have had very successful grows, so I know the requirements and everything. I'm an engineer and I've planned this room really well (not bragging, I swear). I'm not asking about the sealed hood, the smell and the scrubber, air circulation inside the tent, etc... I'm trying to figure out the best way to exchange the room air, which will not be warm, and will not have any odors. I'm asking about positive and negative pressure in the room itself.

 

[JSB99]

I swear I didn't make this room complicated just for the sake of being complicated LOL Maybe I'll put a diagram together to show how it's set up.

 

[OldMedUser]

High JSB99

I grok your setup and you should do fine with the 4" as the heat from the light has it's own separate cooling. A 6" fan on half speed will move more than enough air to keep that hood as cool as it's going to get. I don't hook up my scrubber until it starts getting stinky outside and my 6" fan is barely managing to move enough air to keep my temps down to 80F with it hooked up. It's an old scrubber and I'm looking into getting an 8" or even a 10" inline to be able to connect 2 - 6" lines from 2 grow spaces but that's another story.

The main reason to keep negative pressure in a tent is so that no stink leaks out into the room itself. If you are going to exhaust the tent air into the room itself it will be scrubbed and as long as the tent is closed then any air from it has to go thru the scrubber to get out. As it's only a 4" exhaust your intakes should remain passive so there is some negative pressure in the tent and you may have to close some intakes to keep a bit of neg pressure in there.

I would get a larger fan to circulate air in the tent or add another one or two of those small ones to keep the air well mixed up tho with just the one plant for now it's not a big deal.

Looking good!

 

[JSB99]

High JSB99

I grok your setup and you should do fine with the 4" as the heat from the light has it's own separate cooling. A 6" fan on half speed will move more than enough air to keep that hood as cool as it's going to get. I don't hook up my scrubber until it starts getting stinky outside and my 6" fan is barely managing to move enough air to keep my temps down to 80F with it hooked up. It's an old scrubber and I'm looking into getting an 8" or even a 10" inline to be able to connect 2 - 6" lines from 2 grow spaces but that's another story.

The main reason to keep negative pressure in a tent is so that no stink leaks out into the room itself. If you are going to exhaust the tent air into the room itself it will be scrubbed and as long as the tent is closed then any air from it has to go thru the scrubber to get out. As it's only a 4" exhaust your intakes should remain passive so there is some negative pressure in the tent and you may have to close some intakes to keep a bit of neg pressure in there.

I would get a larger fan to circulate air in the tent or add another one or two of those small ones to keep the air well mixed up tho with just the one plant for now it's not a big deal.

Looking good!

Good deal! Thanks for taking the time to go over some things. And you're right, I should close up some of the micro vents to create a little negative pressure in the tent.

I knew I could keep the hood cool, but I wasn't sure how a 4" exhaust fan with a scrubber would do for the tent's exhaust. Without the hood heat, it's working really well. I was trying to do this all for under $1,000, so I had to carefully weigh where I could get away with less. The hood stays cool with the 6" at medium, but the 4" is 3/4 to full at the toasty part of the day.

As far as additional fans for circulation, I have 2 x 6" clip-on fans in the corners, off-center so they lightly breeze the canopy, but create more of a circular flow around the tent space.

 

[JSB99]

A 6" fan on half speed will move more than enough air to keep that hood as cool as it's going to get.

What are your opinions on venting the hood air into the attic. Since the attic's relative humidity is about the same as outside, would exhausting outside air into the attic be okay? I can add an outside vent in the attic if needed, but if not then I probably won't bother.

 

[fsdhy1]

I think you may have missed how I have this configured. The hood is sealed properly, meaning that the air is totally separate from the grow. The 440 pulls air from under the house, through the hood, and into the attic. The 440 pulls no air from the room or house at all. It is dedicated to the hood.

Sounds like he's thinking the same thing I am, which is.... Do you really need a separate circuit for lighting? For a 4x4 tent with a single 600W this seems like overkill. Can you not get away with passive intake from the room and the 440 CFM fan as exhaust pushing through the light creating a negative pressure environment in the tent?

I run the same tent in the same type of set up and that's what I do. In fact, my temps are a couple degrees lower than yours (which could be due to the fact that my wife loves the A/C cranked!). But I'm running two less fans...

If you were running multiple lights I understand segregating the light cooling. But I'm not convinced it's necessary here? No disrespect.

 

[JSB99]

Do you really need a separate circuit for lighting? For a 4x4 tent with a single 600W this seems like overkill.

I could have used a single fan for the tent, but there are a lot of advantages to keeping the hood isolated, and it's actually the correct setup for an air cooled hood. Keeping the hood air isolated makes it so much easier to maintain the temps. Much more hands-off. It also allows me to get away with using a smaller fan for the tent exhaust. I don't plan on injecting co2 right now, but it's all set up if/when I do decide to do that. The cost to go this route was only about $100 more. I thought it was worth it. I've also hated the idea of exhausting house air outside even since I started growing. Seems like such a waste.

There are other advantages that I'm sure you all know about, so I won't go on and on.

If you were running multiple lights I understand segregating the light cooling.

I'm planning on adding another 600w at some point. I wanted to go that route over a single 1k, but the second light wasn't in my budget yet.

No disrespect.

No offense taken at all. I learn a lot from criticism and don't pretend to know it all, so keep it coming

 

[fsdhy1]

Yeah if you were running two 600W, or especially a single 1000W, in a 4x4 I wouldn't have spoken up... I totally get that you're future proofing. Just figured I'd mention that a single 600 is the perfect HID setup to avoid a complex cooling system!

Trust me, I don't know shit. I just know I have the same tent in the same sized room lol


Hey I'm curious what those black straps are that hold up your filter? Looks much better than my chains. You do clean work, kudos.