Rectangular Duct Work Question

Sure, but that room may be much cooler. It is not any different than closing the damper on the register to cut flow by about half.

You can do anything you want but obviously you are choaking both of them down by 50%. Not the greatest idea but It might increase air noise just a bit?? How many other home owners in your home may have done something like what you propose? You can:

Maybe. If they just service one room you can measure the area of the register openings. Your duct is about 40 sq. inches. If the opening area of the registers is much less you can probably reduce the duct size. Generally you want the area of the duct to be greater than that of the register opening to keep the resistance to air flow low, but if the register opening is only, say 2x9 then you might get by ok. But you run the risk of that room not getting adequate heating/cooling or uneven heating/cooling because of insufficient air flow. Cooling is usually the issue on second floor rooms.

You also have to consider whether you'll be reducing the air flow of the whole system enough to affect the furnace, but that's pretty unlikely in your case.

You'd be better off moving the duct to the next stud bay if you can. Of course, that's probably much more work. Easier to do it now though, while the wall is open, than to have to open it back up when the room doesn't get warm/cool enough.

HTH,

Paul F.

they might try taping over 1/2 of each register and see how things work.

a second floor bedroom in a air conditioned home might not coool properly in summer but be warm enough in winter