About a month ago, I did my own Manual J (with assistance from the pros here) to give myself an idea of a properly sized heat pump for my home. After posting my calculations for my 1412 sq ft house in the Portland, OR metro area, the consensus was 2 ton heat pump.
I just spent a decent amount of time looking at the ducting in my attic. This was a huge chore because I have vaulted ceilings in the house, thus, there is only about a 3-4 foot tall "attic" to crawl around in. I pretty carefully researched all my ducting, noting the sizes of everything. I diagrammed my findings below in a "to scale" drawing of my home. Basically, all I have is flex ducting and the widths range from 5" to 8" for hot side, and a 14" width for the return (20x20 filter).
I'm going to have a heat pump with electric backup installed, and a leak test will be performed before hand to make sure the house ducting is sealed properly.
**My question to you guys: I intend to stay in this house for about 4 more years. I don't want to change the ducting if I don't have to because that would be a huge additional cost. I feel like the air at the farther end of the ducting system should come out with more force than it is with my current hardware. Can anybody look at my findings and tell me what range of CFM for my air handler I'd be looking at?**
Here is a photo of the return supply:
Here is a panorama of me sitting on my air handler and looking down the long end of my "attic" (note that my ducting is virtually all covered by cellulose):
Below is a diagram with measurements of my flex ducting and appropriate widths
Thank you for your time.