Exhausting 2 smaller grows into a furnace duct?

Im moving my stuff into a reclaimed sauna for seclusion among other reasons (30 amp breaker, tile floor with a drain, insulated walls and all around pretty cool temps to start with. For my design im think of leaving the door open and having passive intakes drawing in the naturally cool air in my basement. I have 2 grow areas ones a keg fridge grow box and the other is a 4x2x6 tent.

Inside the sauna, a furnace duct (running to my bedroom) spans along the length of the sauna in the top back corner. It pushes hot air in the winter.

Both my areas are hoing to be exhausting hot air into the sauna and i need a way to direct it all out. Now i can run 30+ feet of 6" duct to a window, or i can use the furnace right above my tent.

The issue ive thought of wpuld be backward draft when the furnace comes on (hot air coming into my hot grow areas) which would be unaccteptable, ive thought of using flap-style vents, and things of that nature and stumbled upon a future possibility ( back draft dampener) i think i can manage it simply with airflow by leaving my exhaust's running full time.

Worried about my furnace fighting thw tents i decided id potentially install the exhaust on a 45 degree going with the airflow of the furnace.

My questions are would i need to match my cfm in the bigger area with my smaller area ? Im worried if i run a 4" and 6" exhaust fans into a y adapter. It may lush back into thr smaller tent?

Can i use a booster fan after both tents to help push into the furnace.

Im going to run the exhaust fans 24/7 but ill let them each take a 2hr break when the lights go off and its cooled down... Will this work?

Excuse my drawings, im not an engineer

Opening the venting system of the heater will likely change it's operation or efficiency. I strongly recommend against it. Especially if it's gas fired.

Carbon monixide!!

As soon as you tap into that heater exhaust you are going to put a positive pressure on it. When the heater kicks on, the exhaust will have difficulty getting out freely because it is competing with the pressure from your grow.
There is another problem. Unless your heater has a one way valve coming out of it, and it doesn't. When the heater isn't running some of your air will be going out the top of your house, some will be going out of your heater. The path of least resistance will be your heater.
Maybe another problem. Is your water heater in the exhaust loop? Because it works off of hot air rising to exhaust, something your fan will not let happen, so your water heater is exhausting into your house as well.
Don't do it unless you know exactly what you are doing.
No one like waking up dead.

As a former and still licensed heating technician I recommend no one ever vent out a chimney. Run 30 feet of ductwork instead

I'd consider knocking a 6" hole in a wall, be it concrete, brick, block, wood, whatever. Check that option out.
Check this link out. I see these all of the time. https://www.google.com/search?q=rad...UIylMKHfZYAv8Q_AUICygC&biw=1080&bih=623&dpr=2
They are on just about every home where I live, I don't know about you, but it is an option.
Obviously use it to vent your room, not for radon. My actual radon fan is inside, so I just have a pipe running up just like those, but no visible fan, and that is common, too.

Another option like that maybe is a dryer vent. I can tell you that a 6" 440cfm with about 6 feet of duct sounds exactly like a dryer running from outside the house.

You could also pay to have someone install a chimney for a wood stove. They would route it outside. It wouldn't be weird because that's the first step in getting a wood stove installed. Then use that.

-Oh, and yes. Having your 4" and 6" on a Y will make them both struggle unless you went with an 8"+ Y, and have the fans always run at the same time or else one will push into the other. You could run a one way flap on the 4" (cheaper) to alleviate that problem, though. 8"+ is a pretty big exhaust pipe. You could still run a 6" Y with flaps on both, but you wouldn't be able to run both fans at the same time.

I assume you are running 2 rooms or light heat and tent heat separate? Either way you might be able to get away with one fan this way:
Put the fan in your veg room and have the intake be the flower room, and the flower room's intake cool air. Your fan will pull air through your flower room and out your veg room. Control temps on the flower side. The veg side is the least important of the two. It might work in your scenario, it's an idea.
If running 2 fans because of vented light heat, do the same thing. Your room exhaust will be the light intake. Run the fan with the light, use ambient temps to control room temps.

Or maybe take two of these ideas, or other ideas and use them. Going 2 into 1 is going to be a pain. I'm no professional though.

Thanks big perm been watching your build silently for a bit now, im just gonna suck it up and put it in my spare bedroom, i really wanted the tile floors and cooler temps in the basement but oh well i can vent directly out my window up here, just a couple pics of what im working with. Light will be distributed between a 150w hps and 2 150w led panels i made. I think theyre brighter than the 150 but i havent done any tests yet. Excuse the mess. And heres one of my outdoor girls this year.

Awesome! I love seeing people DIY stuff. My only recommendation looking at that window is try to get temp and rh dialed in inside the tent. Depending on your climate that might be easy, or difficult. If you can't it's not a huge deal, unless you are WAY out of bounds on something.

grilledcheese101 said:

been watching your build silently for a bit now

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Stop in and say high sometime. It's pretty lonely in there.

DemonTrich said:

Carbon monixide!!

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This. Find a way to exhaust outside. No better way. Get rid of that hot stale air!

I just ran across the same thread somewhere else. I thought you were going out your heater exhaust, too.
https://www.rollitup.org/t/exhausting-2-smaller-grows-into-a-furnace-duct.975052/
Let me re-think this now...well I guess now it doesn't matter.
Over here all the talk was about furnace exhaust, over there all of the talk is about it actually being HVAC ducting. Spreading the same topic in multiple places gets confusing.

Big Perm said:

I just ran across the same thread somewhere else. I thought you were going out your heater exhaust, too.
https://www.rollitup.org/t/exhausting-2-smaller-grows-into-a-furnace-duct.975052/
Let me re-think this now...well I guess now it doesn't matter.
Over here all the talk was about furnace exhaust, over there all of the talk is about it actually being HVAC ducting. Spreading the same topic in multiple places gets confusing.

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Ya idk why but it posted twice at the same time, lol some people read it right some didnt. I was planing on using the hvac ducting, im not completely stupid - just a little. But i decided against both

What have you got in the 2 150's for led's?

grilledcheese101 said:

Ya idk why but it posted twice at the same time

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I see. I thought you did it on purpose. I actually didn't realize it was in the same forum, I just came across it and was like...wtf, where are my posts?

Big Perm said:

What have you got in the 2 150's for led's?

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Theyre just dollar store bulbs 9w 800 lumen

grilledcheese101 said:

Theyre just dollar store bulbs 9w 800 lumen

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Costco has some 3000k 17.5w 1600lm at a decent price, fyi.