[PapaHepcat]

Forgive the n00b question, but is it okay to add a grill directly to an existing return duct? The duct is in the basement, rectangular and exposed. The basement is partially finished. There's already a register in another part of the room, but no return. I need to have better circulation down there.

 

[user_12345a]

You can as long as it's not near a furnace that pulls combustion air from the house.

It will be noisy and you would have to go for a smaller than normal size to avoid drawing air too much from the basement, putting it under negative pressure.

 

[beenthere]

Don't know why it will be noisy.

 

[Bret86844]

Just keep in mind that you will be stealing air from some other part of the house. So you may want to find one with a built in damper so you can adjust it easily.