OK, followed industry recommendations over the years and fixed everything I could find:
1) Added Attic insulation
2) Attic Power Vents
3) Mastic sealed vents
4) Keep clean filters
5) Replaced single pane windows with dual pane
6) New roof tiles (not related, but cost so dang much I threw it in)
Three (3) HVAC systems:
- 2nd Floor Tempstar 9000 Model Number CA9036VKC1 (3 ton?)
- 1st Floor Bryant Model Number 565BJ036-A (3 ton?)
- Basement Comfortmaker Model Number AG024 GB2 (2 ton)
We keep everything set at 75 / 76 degrees and the systems don't run for long. Oh yes, its approx 6,000 sq ft total space. Humidity stays around 45-55%, and now the air coming out is only about 7-9 degrees cooler than return air. So, after three years I think I'd better call service and get a checkup.
Any suggestions on what I should ask for or look for? I'm guessing that the Manual J numbers have changed significantly, but don't see a reason to downsize yet????