Ventilation—Wye Duct & Sizes

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vtguitar88

Well-Known Member
Sup Rollies,

I have a 4x4 veg tent and a 5x5 flower tent nearby each other in the same small office and it's getting HOT in there. I live in one of the hottest places in the world and our 3-week long winter is officially over, so I can't vent into the room anymore. I just bought a 6-inch exhaust fan for the 4x4 (was running on a 4-inch plus a separate 6-inch booster—budget problems), and I want to run flex duct from that fan and from the 6-inch fan/filter in my 5x5 up to a Wye or Tee duct connector, and then run a final line along the ceiling and up into my attic.

2 questions:

1) Since I'm just exhausting, i.e. using fans to push into smaller lengths before the duct splitter/combiner, can I get away with a 6x6x6 tee/wye connector? So I'd be sending the two 6 inch exhausts into the connector and they'd combine into a single 6" duct and zip out into the attic. Is that going to create too much of a bottleneck, or back pressure that could damage the fans?

2) Where is the best place to utilize the 6-inch duct booster fan that I've had in my veg tent? I was thinking either right after the Y/T connector, or at the very end of the line, to give the exhausted air a last boost up into the attic.

I really appreciate any input here. My instinct is telling me I might need to go up to an 8-inch duct for the final long run, but hoping I can get away with 6/6/6 connector because they're cheaper and easier to find than 6/6/8
 
Renfro

Renfro

Well-Known Member
vtguitar88 said:
combine into a single 6" duct and zip out into the attic.
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Exhausting warm humid air into the attic is a big no no. The warm air cools and the moisture condenses on surfaces in the cool attic. This results in black mold. Very expensive to remediate. Best to exhaust outdoors directly.
 
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vtguitar88

Well-Known Member
Renfro said:
Exhausting warm humid air into the attic is a big no no. The warm air cools and the moisture condenses on surfaces in the cool attic. This results in black mold. Very expensive to remediate. Best to exhaust outdoors directly.
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Good call, except I live in Phoenix, AZ, one of the hottest, driest cities in the world. There's also an existing exhaust fan in the attic that exhausts the hot air out 24/7 already. If I run the duct right up to that roof vent fan, do you think I'd be ok? It's already back to being 77 or 80 every day and 50's at night, with low double digit humidity most days.

My only other option since this is a rental would be sticking the duct in a nearby window. Even though I'm a totally legal rec grower under AZ's new Prop 207 (can have up to 12 plants per 2-adult household), I don't live in the greatest neighborhood and don't want to advertise "free weed here" by sending ducting through an opening sliding glass window.
 
redi jedi

redi jedi

Well-Known Member
I think you'll be fine but its not the best idea. Anyways, use a wye and your booster after the wye isnt a bad idea. Will both exhaust fans always be on?
 
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vtguitar88

Well-Known Member
redi jedi said:
I think you'll be fine but its not the best idea. Anyways, use a wye and your booster after the wye isnt a bad idea. Will both exhaust fans always be on?
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Yea at least for now while tent 1 (5x5) is in home stretch of flower and tent 2 in late veg. Sometimes in early veg I’ll turn off exhaust for the 6 hours lights are off. I have an extra 4 inch fan and filter so planning to use that as my 24 hour flower tent fan in early flower and use the 6 inch fan/filter while lights are on.

Why would you say it’s a bad ish idea? For the mold concerns mentioned above? I just moved to Phoenix last summer so I’d be curious if anyone from here can chime in about potential mold problems. Definitely seems implausible but anything is possible. We had a really rainy week last week but otherwise it had lightly rained twice at my house since I moved here in June. Central Phoenix got just under 3 inches of rain total in 2020
 
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vtguitar88

Well-Known Member
Renfro said:
The duct restrictor "fan" can go in the trash if you ask me. I would bet on better performance without it.
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That bad huh? I’ve always had a low opinion as well. I picked it up bc I had one of the shitty plastic 4” exhaust fans for my 2x4, but in a matter of a few months I’ve expanded from a single 2x4 to a 4x4 and a 5x5 and didn’t have new fans in the budget till now. So I picked up the 6 inch booster fan to give me the cheapest extra exhaust I could get in my 4x4. Was like 18 bucks. But it sucks. Maybe I’ll sell it for 15 lol
 
redi jedi

redi jedi

Well-Known Member
Without dampers in each leg, you will get back flow when one fan is running. The booster fan may help create a path of least resitance...air flows in the intended direction.

And yes its a bad idea because of the mold concern. Its not bro science, hot moist air into an attic is a recipe for mold but you might be ok given your location.

I think you should also ask yourself if you would vent to your attic if you owned the home...
 
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vtguitar88

Well-Known Member
redi jedi said:
Without dampers in each leg, you will get back flow when one fan is running. The booster fan may help create a path of least resitance...air flows in the intended direction.

And yes its a bad idea because of the mold concern. Its not bro science, hot moist air into an attic is a recipe for mold but you might be ok given your location.

I think you should also ask yourself if you would vent to your attic if you owned the home...
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Excellent point about the back flow. I probably wouldn't have thought of that until it was happening and I realized why. I'll most likely just plan to run them both 24/7 in that case.

Re: mold, I definitely don't want to trash my landlady's rental bc we're on friendly terms. I will try to do some more research into whether black mold is a thing here. Did you check out the short video I posted of my attic? What if I ran the final duct right up to that exhaust stack and just clipped it right to the edge of the cylinder? That sticks up on top of my roof so it would have the air pretty much directly exiting the attic into the exhaust stack.

Also, still interested to hear thoughts on my first question, re duct sizing. I actually decided to go with a 6-inch Tee connector and a 6 to 8" duct reducer/increaser. So I'll be running the veg and flower 6" lines into the 6x6x6 tee connector, then attach that to a 6"->8" expander, then run about 24 feet of 8 inch flexible duct up to that exhaust stack in the attic. That seemed like a better call than sticking with 6 inch ducting all the way out. Is there a better way to calculate that?
 
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vtguitar88

Well-Known Member
Also I have an extra 4” filter laying around. Can I put a 4”- 6” expander on the —> side of the filter and attach it to a 6” fan? Can’t seem to find any answers to this on the Google
 
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vtguitar88

Well-Known Member
redi jedi said:
Too small for the fan
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Do you think it would damage the fan by essentially throttling its intake? This is obviously unconventional bc I can't find much mention of it. And I know the filter would be less effective due to reduced carbon surface area. But it seems like with a tightly attached reducer, the 6" fan would pull through the smaller filter just fine, right? Thanks again for your input
 
eddy600

eddy600

Well-Known Member
I live in an area with low humidity like you and vent up into my attic without any problems for more than 20 years. The only time you might need a carbon filter is during the monsoon season. I just put a filter in my closet to dry my outdoor weed 15 to 20 lbs will create quite a bit of smell outdoors,probably a 100ft circle of heavy smell. A couple pounds no one will notice the smell as long as your inline fan is pulling air.
 
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