Can I use existing duct work?

Hey All! I am currently building a grow room in my basement and had a question about exhausting into existing duct work, the duct that I want to connect to carries warm air to a room upstairs, would it be safe connecting to it using one of these?

That will work, just make sure you have it pointing the right way. If your going to use this system then it will seem like your furnace is always on no? Make sure you have a good carbon filter otherwise your whole house is going to smell like weed.
I would also install a backdraft damper on your house air duct supply side so it wont pump air into your furnace when its not on.

Thanks for the reply! It's fine if it seems like the furnace is always on in that room, hardly ever in there, plus I was wanting to use the heat from the grow room to help heat that room because it gets pretty brisk during the winter. I didn't even think about a damper, good suggestion. As for the smell I have a carbon filter so smell shouldn't be a problem.

Connect it with a damper. Don't mess with the furnace or its venting. You could cause CO leakage.

Remember carbon filktwr don't work that well in full flower