Hi. New to this forum here. I'm a big fan of DIYing. I don't know everything, but like to learn stuff and do it on my own. Previously, I have replaced windows, renovated my kitchen, put in new recessed lights, done tile work, etc, all by researching beforehand as well as learning as I went along. But I've never done any HVAC work before. So here goes
My main furnace/blower is up in the attic and has a hard time warming up the 1st floor adequately during the winters. Well my basement has a separate furnace/AC for the basement alone. I recently replaced this furnace with a new high efficiency one since the old one was dying. I'd like to cut out some 4"x10" floor registers on the 1st floor and extend the basement ductwork to share some of the heating between basement and 1st floor. That way, 1st floor will be heated mainly by main furnace up in attic, but also by basement furnace when it kicks on.
First of all, this is the layout of my basement. As you can see, current duct runs along right wall, almost the length of the basement
I'd like to take part of the duct down, and cut two holes on top to create feeds for the new 1st floor registers.
(1) register will sit right on top of where duct lies. So that new duct will just go straight up between the ceiling joists and thru the ceiling/floor.
(2) register will sit on the other side. So for this one, I'd like to up from the current duct into the ceiling cavity, make a 90° turn and go across between the ceiling joists so that I can have a flat ceiling when I finish off the basement.
This is my plan anyways. But since I've never done this before, I'd like to know if there's something I'm not thinking of, or not aware of. How big of a duct will I need for the cross run? Will a 7" round suffice? The cross run will be about 13-14'. What other materials will I need? What should I know when performing this. Any info helps. Thanks