I live in Memphis, TN in a 3400-sf brick house with 2100 sf and 9-foot ceilings down, 1300 sf and 8-foot ceilings up with an entry way that's open to the second floor. The first-floor master bath also has a raised ceiling.
I need to replace the existing 18-year-old dual systems which are currently 4-ton A/C down and 2.5 tons up. Furnaces are 78%-efficient gas. The current downstairs system, even after a Freon charge, does not sufficiently cool the southern half of the downstairs when the outside temp exceeds the low 80s. Now the condenser motor on the big unit needs replacing and the attic flooded three months ago, necessitating replacing the decking underneath the furnaces, so I'm taking advantage of the cool weather to just replace everything.
I've gotten three similar bids for the following. Going from the current 8.5 SEER units to 13 SEER units should, of course, result in significant electricity savings. However, all three contractors have stated that going from 13 SEER to 16 SEER or higher will not result in enough extra savings to recoup the difference in equipment cost over the life of the units. The 95% furnaces will qualify for the $1500 tax credit, so the SEER ratings of the A/C units are not an issue. All have ECM VS blowers.
1. 4-ton and 2.5-ton Amana GSX13 13-SEER units w/ GMV95 100,000 BTU and 70,000 BTU 95% two-stage gas furnaces.
2. 4-ton and 2.5-ton Trane 13-SEER units w/ 95% gas furnaces. (Bid didn't specify models or furnace sizes.)
3. 5-ton and 3-ton Coleman 13-SEER TCGD series units w/ LX series 120,000 BTU and 80,000 BTU 95% two-stage gas furnaces.
All seem knowledgeable and own reputable companies. No. 3's reasoning behind suggesting the larger units was that with our ceiling height and the layout of the first floor, the 1 ton/500 sf rule doesn't necessarily apply and the fact that our current 4-ton unit has never effectively cooled much of the downstairs. I realize you can have too much tonnage, too, but he's convinced these are the optimum sizes for this house. Prices are all close with #3 being slightly better.
Is it really worth the extra $ to get the 16-SEER units? The charts (you guys love your charts!) indicate we'd expect to save, on average, only about $50 a year by going from 13 to 16 SEER.
What is your opinion of "balancing" by partially shutting off vents on the "cold" side of the house to try to cool off the "hot" side of the house versus installing air duct dampers and/or increasing the size of some ductwork? That's what one guy suggested, and that option is cheaper, but does it put any extra "strain" on the system to do this? In a way it seems logical to me it could, and another guy said it could potentially cause the coil to freeze up. There is also the question of whether the existing downstairs ductwork is adequate for a 5-ton system.
I'm just trying to wade through all the conflicting information. Any advice would be appreciated.