I’d like some more professional HVAC opinions on my dilemma. We have a two story home with forced hot air heating. Added central A/C recently. Plenty cool downstairs, upstairs not so cool. The r/a consists of two 2 x 12 joist bays, 16″ oc, panned off in the family room with a 16 x 32 ceiling grille. From the grill to the can on top of the furnace is 14′. The second floor return consists of one 2 x 4 stud bay that is stacked above the first floor return. The bottom and top plate of this bay was removed and at the top, a transition piece was installed to a 12″ round flex duct, connecting to a 12 x 24 ceiling grill on the second floor. Doesn’t seem like a single stud bay would provide enough volume. The stud bay is in a wall that separates two back to back closets. I can easily remove the top and bottom plates in the second stud bay, doubling the volume, but am wondering if it will be enough. I’ve looked for other ways to try to rout another return, with nothing available except an outside wall, which is not an option.
Any suggestions are appreciated.
Thanks,
HV
Replies
I think you're on the right track.
The stud bay is good for maybe 200 CFM, under ideal conditions, and your conditions are less than ideal, since the air will take the path of least resistance, which is thru the big downstairs grilles.
This is especially true if there's a door separating the upstairs from the downstairs.
Also, the addition of the cooling coil in the air stream will have created extra resistance to the airflow you previously had, thereby reducing the CFM that the blower can deliver. This also means that less air will be pushed to the registers farthest from the blower.
So if I open up the second stud bay, should I place some horizontal baffle in the floor joist bay, say four inches down and a foot long to create a venturi effect? After the R/A is opened up, is there any merit to the inline duct fans to help boost the flow on the longest supply runs. If memory serves me, the supplies in the crawl space that come off the trunk are eight inch rigid and transition to a four by ten oval to get to the second floor floor registers.
HV