Hello all, this is my first posting so be easy on me. I have approximately 1737 sq ft brick ranch, single story home located in the Charlotte area that was built in 1982. My home originaly had a 2.5 ton heat pump and was replaced in '97 with an Amana high efficiency furnace AC split system. Spec's on the system are as follows:
GDC090X40B horizontal gas furnace
RCC36A2B AC unit
The original duct work was kept. I'll try to the best describe the current duct system.
Supply trunk (one continuous trunk) with:
8"x8" x 14' section with 3 - 6" supply branch runs
8"x16" x 25' section with 6 - 6" supply branch runs
8"x8" x 8' section with 3 - 6" supply branch runs
So I have 12-6" supplies to my rooms. All duct is hard ducted and insulated to R-5.
Single return (I know this is bad from what I've read on this site) in hallway cemter of house:
16" flexible return trunk
20x25 grille using disposable filter
Last year I had to have the compressor replaced and here's the numbers the technician wrote on the receipt:
Outside temp: 88 deg F
Pressures: Low - 85psi, High - 275psi, return air temp - 80 deg F and supply air temp - 65 deg F, delta temp - 15
I read enough about HVAC designs to be dangerous, but I ran a duct calculator program I found on the web site and here's what I found:
Supply: assumed 1200cfm, 750fpm > 17.13in round
Return: assumed 1200cfm, 500fpm > 20.98in round
1. Does the duct system design sound like it will function ok for the 3ton system or does it need to be replaced?
2. What are the recommendations for getting return paths back to the central return? jumper duct or transfer grilles? I am especially concerned about the master bedroom because it has 2-6" supply trunks and 1-6" for master bath.
Using a transfer grille for the bedroom would mean cutting about a 14" square hole in the wall which would look terrible. Can't put transfer grilles above door due to construction.
3. From the numbers I got, seems like the return is undersized. Does this sound right?
Sorry for such a long post, but wanted to give as much detail as possible. By the way, I also had to replace the horizontal coil due to a leak. So I'm frustrated with the whole system, but thats another story. Thanks in advance.