Hello all -
1.5 story house with two systems - one does the main level and basement, the other does the upstairs 1/2 story.
The upstairs system is very noisy - too much fan, not enough duct. When we first bought the house, there wasn't a filter in the unit. We put one in and realized why - the return plenum started vibrating. Luckily, we had a piece of styrofoam that was the same size as the space between the blower and the return plenum, and that got rid of the vibration.
However, the unit is still quite noisy - presumably because of the load on the fan to blow the required air (and the resulting velocity). I also have one room that gets too cold in the summer (several degrees difference between room and hallway). I tried to adjust the register damper to reduce the air flow to that room, but I could not make much adjustment before it started whistling.
The blower unit is in a closet. From the blower unit, the supply and return plenums go up 8-10 feet into the attic area. Once in the attic, the supply is routed to one 6" flex to a bathroom, and three 8" flex ducts - one to each bedroom, and one over the living room atrium (18' high walls). For returns, three 10" flex - one in each bedroom, and one in the hallway between the bedrooms. No kinks or hard bends in the ducts, and all are well sealed to the plenum.
Based on some load calculations, here's what I've got:
Bedroom 1: 165 sq ft, 2900 cooling (2425 sens), 3500 heating, 230 cfm
Bedroom 2: 185 sq ft, 5450 cooling (4675 sens), 5925 heating, 115 cfm
Bathroom/Hall: 95 sq ft, 2275 cooling (1650 sens), 900 heating, 80 cfm
Total: 450 sqft, 10625 cooling (8950 sens), 10325 heating, 425 cfm
Keep in mind - I've got a register over the living room/foyer to dump the extra air - it's 560 sqft x 18 feet tall, but is primarily served by the main unit.
The system is all 5yo Comfortmaker. Outdoor unit is 1.5 ton 10 SEER. Indoor unit is 2 ton blower (MF08B1500A2) and coil (EPA24B15B1). 4.8kW heat. According to the manual, on low tap it provides 850 cfm at .7" (with .5 of that going to filter, coil, and heat element).
My plan is to increase the supply flow to both Bedroom 2 and the Living Room, as well as increase the return duct in the hallway (which is directly outside the door to Bedroom 2). I believe this will help with some of the stack effect as well, since it will encourage more bedroom air to mix with the hall air where the thermostat is.
I was thinking changing to 10" into Bedroom 2, and 12" into the living room, with the hall return 14". But would this be going too far?
Sorry for the long-winded question, but I know some of it would be asked if not provided.