I just replaced my entire 1984 vintage heating and cooling system after nursing it along for the last 5 years. The AC went out first and finally the heater went completely out a year ago this month. I used the Costco program and put in the state of the art most efficient system that Lennox makes. They came out and cleaned and sealed all of my duct work, and installed that super duper air purifier system for $24,000.
My duct work leaked so bad that the estimated size of the hole would be 300 square inches. when they were done is was just less than 9 square inches.
Got my 15% Costco discount and 2% Costco Executive rewards.
My average annual power bill was close to $7,500 year for a 2,400sf home. The system is saving me $400- $500 month in the summer and up to twice that in the winter and now my average power bill is between $185 and $215 month now.
I forgot to mention that we set the heat at 65 over night and at 68 when were home. Summer AC temp is now 72.
Before that to even cool the house was 68 and to heat the house was 72.
If I put it on 70 it will get way to warm in the winter and too cold in the summer.
My next project will be to replace the windows and insulate the floor.