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4x4 LED tent ventilation question from a n00b.

SweetJ138

Member
I'm currently building my 4x4 grow tent set up based around the Kind LED xl750. It is in my finished basement, in a corner surrounded by 3 walls. I posted the temp and humidity level of the tent with nothing running yet. My plan was the run a 4" exhaust fan with carbon filter out the rear port, and run ducting above my bathroom, which is next to the tent.



Could i just stop there, and have that air just blow back into my house? Again, there will be a carbon filter, and any heat it gives off will be fine with me, as the basement is cool all year round.



Or could i splice that ducting in to my current hot water tank exhaust duct, which leads outside?


I'm trying to avoid having to drill through my walls to add another exhaust duct just for a small led based set up.



Also, as far as air intake goes, would a 4" intake fan with a carbon filter or horti-control dust shroom be overkill? or should i just expect to be able to get good enough intake from the rectangle ventilation ports on the bottom of the tent?

I will be running one or two 6" clip on fans on the inside for circulation.



Any advise would be greatly appreciated.
 

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SweetJ138

Member
oups... pics are sideways... the 2nd pic is to show the space where i was going to run the exhaust ducting. out the back, and over the bathroom which is behind that wall on the right.
 

SweetJ138

Member
here is a pic of the other side of the bathroom where the ducting would lead. That is the hot water tank exhaust that leads outside.
 

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Douglas.Curtis

Autistic Diplomat in Training
I personally believe a 4" fan to be too small for a 4x4. I use a 6" and get close to 3 air exchanges per minute.

I have not used tents with only square vents before. I make or use tents with multiple ducting in/out sleeves. Is there a round, ducting type vent near the top anywhere? If there is, I'd use it as an exhaust, pulling fresh air in from the bottom.
 

SweetJ138

Member
i can still get a 6"er in there. i haven't gotten anything up and running yet. I could keep the 4" as an active cool air intake if nothing else. I have the port on the top and a few on each side so i could as easily set it up the way you described.


https://420bigbud.com/best-4x4-grow-tent-setup-reviews/#Best_Inline_Fan_for_42154_Grow_Tent

this is where i read that 4" would be "more than enough".

I did notice however, that most of the all in one 4x4 tent kits out there with LED's come with a 6".
 

OldCoolSativa

Well-known member
I use a 190 cfm 4" blower and ducting in the 4' x 4' tent in my basement, and it provides plenty of flow for that size tent; you don't need 6". I bought a speed controller and usually run the blower at less than half speed. I put the charcoal filter on the inlet inside the tent, and I use rigid duct pipe and elbows for the majority of the duct run, which totals about 8' from the intake at the top of my tent to the floor, then into the blower. From the blower outlet I use a short length of 4" flex pipe that I direct into a fireplace chimney. I used a 4" flange mounted to a piece of 1" rigid foam insulation board that I cut to fit into the flue above the damper in the chimney.

The salient question is, will operation of the blower adversely affect the operation of your water heater exhaust? My situation is similar in that the chimney I use for exhaust is also used by an upstairs fireplace and by the exhaust from the oil-fired boiler that heats my house. What you DON'T want is for the exhaust from your tent to overwhelm the ability of the water heater to exhaust combustion gas, which could cause accumulation of carbon monoxide in the house when the water heater is operating. The answer depends on how powerful each blower is, and how much resistance in the ductwork must be overcome by the blower(s). If you use too large a blower for your tent compared to the blower used by the water heater, the backpressure in the ducting could be too high for the water heater's blower to push against. This is another reason why you don't need a 6" blower on your tent. If you want to get fancy you could measure dynamic pressure at certain points in the ducting, but in my case the blower on the boiler is much more powerful than the one I used for my tent, and I've operated it for two years without issue.

Depending on how cold your winters are, you will probably want to vent the blower exhaust into the basement during winter to conserve heat, and re-connect it to your outlet to expel heat in summer. Otherwise, you'll be sucking heat out of your house and inducing infiltration of cold air during winter. Here in New England I disconnect the blower outlet in November and reconnect it in May. One last thing to consider is how tight your house is. New construction, extremely tight houses won't let enough infiltration in and the inlet of the blower can see too much vacuum to effectively move air. In that case your house probably already has a heat recovery unit.

Also, don't bother with noisy axial blowers and use a centrifugal unit instead.

Good luck.
 
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Douglas.Curtis

Autistic Diplomat in Training
I use a 6" with 1000w HID. The site you listed is using LED lighting. This is why the site recommends a 4" fan for a 4x4, they're also recommending a blurple led light. The only time I used a 4" fan was a few months ago, and it was definitely sub-par for a 1000w hid light. :)

Just an FYI, the 4" carbon filter they list is a joke for any loud strain and more than 2-3 plants. ;)
 

OldCoolSativa

Well-known member
I use a 6" with 1000w HID. The site you listed is using LED lighting. This is why the site recommends a 4" fan for a 4x4, they're also recommending a blurple led light. The only time I used a 4" fan was a few months ago, and it was definitely sub-par for a 1000w hid light. :)

Just an FYI, the 4" carbon filter they list is a joke for any loud strain and more than 2-3 plants. ;)

Good point about 4" vs 6" blowers as a function of wattage in the tent, and amount of heat to be removed. My setup is 600W of COBs, but I still think my setup would work with 1KW HPS because the ambient temps in my basement are low, although I'd probably need to increase blower speed.

Regarding loud strains, it is not necessary to run enough CFM to bend the poles of your tent inward to get effective odor control. You only need enough airflow to get a small pressure differential between the tent and the room it sits in. The sides of my tent are pulled inward when I run my blower at 1/8 speed. Additional airflow above this does absolutely nothing to improve odor control, rather, it will just shorten the life of your carbon filter.
 

hush

Señor Member
Veteran
I think that you might be able to just vent the air back into the room where the tent is, and not have to bother with any ducting, to be honest. That's pretty much the exact setup I have. I do have a window unit down in the room where my tents are, but I sometimes even wonder if it's necessary since it stays cool down in the basement year round (I like cold nights, though, because they bring colors out, so I'll be keeping the A/C).
 

Douglas.Curtis

Autistic Diplomat in Training
Regarding loud strains, it is not necessary to run enough CFM to bend the poles of your tent inward to get effective odor control. You only need enough airflow to get a small pressure differential between the tent and the room it sits in. The sides of my tent are pulled inward when I run my blower at 1/8 speed. Additional airflow above this does absolutely nothing to improve odor control, rather, it will just shorten the life of your carbon filter.
Another good point. Your carbon filter should be sized to your exhaust output.

Personally, I run 3 exchanges of air per minute, with the air providing a lot of the air movement to the underside of the canopy and throughout the tent. Am I providing too much airflow? Perhaps some day I'll have the time and re$ource$ to set something up and experiment. Until then I use HEPA filtered air and it works great. ;)

I strongly recommend HEPA filtered air for quality purposes and contamination reduction. The cleaner the air is, the more you can use without increasing your mold/fungi/pollen risk.
 

SweetJ138

Member
I think that you might be able to just vent the air back into the room where the tent is, and not have to bother with any ducting, to be honest. That's pretty much the exact setup I have. I do have a window unit down in the room where my tents are, but I sometimes even wonder if it's necessary since it stays cool down in the basement year round (I like cold nights, though, because they bring colors out, so I'll be keeping the A/C).




thats really what i was hoping for, and so far its looking like that.
my basement is like 60 degrees all year round.

I mounted the light, fan, and carbon filter yesterday and ran everything full blast for a few hours. I got some big time negative pressure, so i put the fan down to half, and was still getting a little bit. temp only got to 71 when running the light full blast and the fan half way.



Now the question is, should i get a smaller inline fan and some kind of air filter (to help fight mold and bugs on the intake), and run it through my bottom intake duct?



Also, i'm looking at for sure adding a small humidifier, but would i benefit from a small heater as well? This LED runs pretty cool. once its the plants start getting larger, should i expect the temps jump much?
 

f-e

Well-known member
Mentor
Veteran
Filled nicely, you may be putting 10L of water into the air each day. Though you should really get your temperature up a bit. I presume there will be some air exchange in the cellar, to loose this moisture and give some fresh air.


A passive intake is usually enough. If you run a duct from the tents inlet point, into the side of a box, it will stop light getting in and out. I say the side of a box, as the top may be open, with an old jumper laid over it. Blocking light and filtering the air. It really depends how much space you have, but a 6" passive intake would be nice, with a filter a square foot. This won't be hard for the exhaust fan to pull air through. If the inlet is restrictive, it's more work for the exhaust (which is more noise) and the tent may look as sucked in as a phet-heads cheeks.
 

f-e

Well-known member
Mentor
Veteran
That inlet plenum (see: cardboard box) is also a good place to add heating. 50w reptile tubes perhaps. To help keep nighttime temperature differentials in check
 

SweetJ138

Member
I went ahead and bought the same inline fan, and a horti-cap to run as a clean air active intake. I'm just set it lower than the outtake fan, and go for that slight negative pressure. I have a pet in the home for starters. plus if i start growing in the next few weeks, i'll be looking to harvest sometime in the middle of spring time. i would much rather have the piece of mind knowing that my air coming in during late flowering is clean.



i have a medium sized space heater, if i ran that near the fresh air intake on the outside of the tent, would that be able to bump me up that 5 or 10 degrees i might need i have some chilly nights?


thanks for your input guys.
 

SweetJ138

Member
quick update if anyone cares, or if anyone has the same questions.
i am well into my first grow with the dual 4" fans. one with a carbon filter on the exhaust, and one with the horti cap on the intake. both hooked up to variable speed adjusters. the exhaust fan is set to about 75-80% in power, and the other to about 40%-50% power. i have slight negative pressure, no smell in my basement, and everything is growing great. Just flipped to flower this week.
v4u3rdg61eh21.jpg
 

SweetJ138

Member
i'm also running a small $20 space heater directly in front of the air intake ON THE OUTSIDE OF THE TENT. Inside, it dried the shit out of whatever plant it was near. However keeping it outside, in front of the new air intake, is working perfect, keeping my temps right where i want them. A small $30 honeywell humidifier is keeping the humidity between 40-60%, however, i was filling it twice daily.
 
R

Rab.C

my house must be roasting i have 3x3 tent 600watt in there. got 8ins rvk on variac 5 step controller at step 3 and temps 25.5c and window open...
 
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