I just bought an older house that had a 2-story addition put on at one time-well i've noticed lately the 1st floor part of this addition is 2-4 degrees cooler then the rest of the house. After some investigating I found one of the two vents for the 22x12 living room that is the addition is not actually hooked up to the heating ductwork. Its like the builder put the ducting and vent in the wall but forgot to go in the basement and hook it up to the heating stack-right now if you go in the basement you just see it come under the floor and stop.
Now my question is this-do I have to hook up this duct all the way to the main rectangular heating stack (and how would I go about making a hole in the heating stack to fit this new duct branch off?)? There is a heating duct that is the last duct that comes off the main heating stack at the end-and this one comes right next to where the unconnected duct is-all i would need to do is tee into this duct to connect to the vent. Do i have to make the ductwork go all the way back to the main stack or can i tee off the last duct that comes out of the main stack which would be much easier?
You will not want to just tee the pipes together. The size of the pipe dictates how many cfm that you will get to that boot. If you tee off the incoming pipe, whichever side has the least resistance will get the most air but neither will get enough. I would hate say that you could tap in anywhere but back at the plenum of the furnace. You may want to have a HVAC company look at it to make sure you have the capacity for the duct to be hooked up. This could be the reason it was unhooked to begin with. I know thats probalby not what you wanted to hear, but to keep your equipment running properly and you comfortable, you will want to do this right.