I'm new to this so please bear with me. I'm doing some work on my house where I have pulled up a section of flooring in a bedroom. I noticed that there are 3 pipes that run from the furnace into the room. 2 of them go to vents in the room but the 3rd one (red arrow) just stops in the middle of the room and was open. Hot air was coming out when the furnace started, but I'm perplexed as to why it's there. The bedroom is above a garage and a buddy suggested it may have been put there to heat it but was left unfinished by the builders. I thought it might have something to do with keeping the floor warm in the space between the garage and the bedroom. There's lots of insulation and a vapor barrier. Can I just cap it with a stopper or should I leave it open? Pardon my rambling. I included a picture.