Hello, New to this forum. I hope someone out there might have some advice. My home was built in 1999, so it's not that old. 2 story 2800 sq ft. Has always had issues with the temperature being 10-12 degrees different between up and down. There is only one thermostat upstairs. I just avoided being downstairs during the winter. My wife and I married in 2004 and she complained about the difference and now we have some money to get it fixed. After having two contractors take a look at what I have, they both tell me the ducting is designed wrong. There are only two returns, 20x25 and 18x18, which they told me will allow only a little more than 1200 CFM and my 5 ton system needs 2200 CFM. So i need to install a new return and then install a zone system with a thermostat downstairs. The whole thing will cost $10K. My question is shouldn't the builder be responsible for this since it's appearently a design flaw? Any advice would be greatly appreciated.