Quote Originally Posted by KitchenKhemist View Post
Yeah, sounds like you got a couple of problems there man. You can get a speed controller to knock that fan down a bit, but it will still pull smoke in from the woodburner if it's operating anywhere near what you want it to. I'd suggest a sealed room with that fan exhausting outdoors...roof or otherwise (dryer vent kits are handy if you can go low through a wall...and they have their own backdraft damper) and a relief-air pipe plumbed from the attic or crawlspace into the room.

Next thing...If you pipe your return ducting into that growroom, it WILL pull air from the room whenever the furnace/stove blower runs. I understand what you're thinking with the "path of least resistance," but it actually becomes easier for the air to enter the duct through 2 openings rather than one....therefore, less resistance (trust me...it's what I do). I'm not sure what kind of damper you are referring to, but unless you get a manual damper that you completely close during the cold months (even then, it won't seal completely), the furnace blower is gonna suck that air from your growspace. If you're carbon filtering the air before it hits the duct, that handles the smell problem, but you've still lost total control of your growroom air ventilation (think CO2 levels, temps, etc.)

I hope I'm not sounding like a knowitall prick...just trying to help. Plus, pulling a negative pressure in the house with a woodburner scares me man.

Just lookin out.
I do have a speed controller (speedster) and it sucks, the fan will start humming before you can even move
it to the medium settings. I've been dragging my feet on getting a variac but I think I need to stop procrastinating
on that.
I don't really want to add a wall vent in that area due to there isn't any reason for one to be there.. It would be the way to go I agree yet impossible to jedi mind trick someone with that.
I do have a bath exhaust near, that was never plumbed out of the attic, I might be able to pipe that through the roof/gable vent and place a y pipe to connect the two and exhaust out? Bath exhaust has a damper on it already.
That concerns me though since I don't want air coming back down through that and I'm not sure how
that fan would perform afterwards with one fan already blowing through the stack.
I would not be returning any kind of venting/ducting back into the garden,
the ductboard is actually in a hallway (2 doors away) where the tie in would happen if it does..
Good point on losing control of my environment and more to think about for future scaling.

I appreciate the insight, that's why I asked for the advice on here. I don't want to mickey mouse it;
just try and save some heating and cooling costs and try not to tear things up to bad that it sucks trying to fix it if I should sell/move down the road.
Either way you look at it, slowing that fan down is definitely one part of the solution
so I can stop the entire house negative pressure.