need help setting up ventilation (pics)

[mr-natural78]

ok. I'm going to put a 450+ cfm fan in my grow room. I need to figure out how to connect my lines from this to the outside. I am in a rural area with wide open spaces around the house so I am not worried about the smell and/or filtering it. From what I can tell I have two options. I can tap into my ducting for the gas furnace and water heater or I can tap into my dryer venting. My dryer vent is only 4" and I would prefer to run 6" lines since my reflector has 6" holes. Tapping into my dryer vent would add an extra 10 ft or so of ducting since it is located further away from my grow area. I could use a reducer and inline fans for that I think, but since it is closer and larger piping I'd like to tap into the furnace/water heater venting. I'm not sure about the safety of this. Here are pictures.

From what I can tell the two join together and then vent outside on the roof. Is it safe to tap into these? I'm thinking I can take off the elbow of larger pipe that you see in pic one and two. Then put an inline fan there (I saw 6" 250cfm fans at meynards for like $30). Then connect a "T" or "Y" section to the inline fan. Last, connect the elbow back to one side and my grow room ventilation to the other. I'm thinking that would prevent any back pressure and keep the air from the grow room, furnace, and water heater all moving out as it should. Any help or advice from someone more knowlegable about this would be greatly appreciated.

Thanks
mr-natural78

 

[FreakNature]

Pressurizing the existing vents would be a problem. I'm not sure what the building or mechanical codes (which are all about life safety) would say about adding a fan to pull your exhaust and avoid the back pressure. You'd be forcing the furnace and water heater to have air flowing through them, rather than the passive act of venting. Not sure how that might affect the operation of either piece of equipment...possibly reduce efficiency or cause issues with sucking out pilot lights.

Your safer option might be running 6" (or whatever your room requires) and use it as a combination dryer vent / room vent...especially if this is an electric dryer. You'd need a backdraft damper in the dryer vent upstream of your room connection.

 

[mr-natural78]

Pressurizing the existing vents would be a problem. I'm not sure what the building or mechanical codes (which are all about life safety) would say about adding a fan to pull your exhaust and avoid the back pressure. You'd be forcing the furnace and water heater to have air flowing through them, rather than the passive act of venting. Not sure how that might affect the operation of either piece of equipment...possibly reduce efficiency or cause issues with sucking out pilot lights.

Your safer option might be running 6" (or whatever your room requires) and use it as a combination dryer vent / room vent...especially if this is an electric dryer. You'd need a backdraft damper in the dryer vent upstream of your room connection.

Ahh, I never thought of that. The fan would be pulling air from the furnace/water heater as well and probably would cause problems with the pilot light or something else. I will take pics of my dryer set up and post them for advice on tapping into that.

 

[mr-natural78]

Ok. Here are pictures of my dryer vent set up. The first pic shows the corner of the garage that the dryer is in.

The dryer exhaust goes through the wall on the right of the dryer. It then goes across the top of the stairs that lead to the basement. You can see the dryer on the left and the basement door on the right of pic 2.

In pic 3 you can see the exhaust line across the stairs. Pic 4 was taken from the other side and you can see where it exits out.

It elbows and goes out just above ground level right there in pic 4. It would take 30-40 feet, maybe even more (I haven't measured yet), of ducting to reach this spot from my garden. Would I need any in-line booster fans for a run this long? Would I need to put an inline fan between the vent outside and the "T" or "Y" connection to prevent back pressure and air from the garden travelling back up the dryer line or would some sort of back draft damper as previously mentioned work ok? Do they make such a damper that I could buy at Meynards, Lowes, Home Depot, etc.? Would I have a problem running my garden ducting all in 6" and then connecting it to the existing dryer line with a reducer? Would this cause excessive noise from turbulance going into the smaller line? Again, any help and/or advice would be greatly appreciated. I have next to no knowledge in this area. Right now it is cool outside so temps aren't a problem in my grow room. I am mostly setting this up to prevent smell inside the building. In the summer, temps will probably be a problem though and I will need this set up to control them.

 

[FreakNature]

450 CFM is gonna take at least 8" at 1300 FPM (a good exhaust flow w/o being too noisey). They do make backdraft dampers, not sure who carries them for you locally. This means it needs to be at least 8" from your garden all the way out the building. The backdraft damper can be sized to fit and installed in the dryer vent before it ties into your new duct.

 

[mr-natural78]

ok. I need to come up with something else then. The existing dryer vent is only 4" all the way out. I'm not really capable of enlarging the opening where it exits. I think the only way this is going to work is just put my lights on that run to cool them and then set up room ventilation that is scrubbed and vented into other parts of the building. This is going to be harder then I thought. I need to do some research. Anyone know a good site with info on this?