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

You have to have a good understanding what your doing when you vent though you furnace stack ,you will run into problems,pushing carbon monoxide back in your house if it's not done right ,not to be taken lightly,

NGA said:

You have to have a good understanding what your doing when you vent though you furnace stack ,you will run into problems,pushing carbon monoxide back in your house if it's not done right ,not to be taken lightly,

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Not my furnace exhaust stack, buddy, my furnace duct. The same air you breath in your own house.

The same duct that a heat register connects to. In theory id be heating my bedroom, with my grow room lol.

Lol ,got ya ,I try to get the smell outta da house not in it,good luck

Extraction fans should be run 24/7, expecially when the light are off to control humidity and prevent mold growth. Venting anywhere into your house is a bad idea because of humidity. All that water you dump on your plants goes somewhere, into the air. Relative humidity above 80% can and will cause water to condence in your walls and grow mold. First signs can be condesation on the insides of your windows. A dehumidifier or two are essential peices of equipment so you dont ruin your home even with proper ventilation.

I have 2 dehumidifiers running in my house. 1 is beside my grow. Also getting a charcoal filter. Ontario sucks.