I am going to be brief, because I have a lot of information to pass along. Bear with me.
4216sf 1 story home built 2 years ago (I am the builder)
Bio-base foam insulation throughout
Unvented, conditioned attic space (insulation on underside of roof deck)
Vinyl low-e windows, insulated doors, etc.
Two (2) 5-ton Amana Heat Pump units
Programmable T-stats set on 82 during the day, 74 overnight
Last month's bill - $688 (approx. 3900 KWH)
Prior month's bill - $461 (approx. 3000 KWH)
Two April Aire dehumidifiers
High bill - generally August / September - $900 +/- $50
No pool, no outbuildings, CF bulbs everywhere, on-demand water heaters
Recently had an energy audit performed. Was told I had one of the tightest houses they'd ever measured in the Houston area; somewhere in the neighborhood of 14% leakage. I went through the house with them with the FLIR camera; no hotspots. Duct leakage on the order of 10% on each system, but it's leaking into conditioned attic space, so I figure that's a wash. Basically beat the pants off the local Energy-Star homes.
Only thing we could figure is the HVAC system is WAY oversized. I had an analysis done prior to building the home, gave to the A/C contractor, they used it for toilet paper or something. I have since gone back and found that analysis and deciphered it, and it appears to show that I need 6.5 tons MAX. I purchased HVAC Calc prior to building, and spent a long time inputting all the correct information. It said I needed something like 4 tons total.
Unfortunately, I caved to the contractor at build-time, assuming he knew more than I did (mistake, apparently). So now, I can't keep the house dry (60% RH or higher, with two dehumidifiers running full-blast), the units short-cycle all day and night, and my utility bills are freaking ridiculous. We are about to pull the trigger on two new 3-ton units (or maybe two 2.5-ton units), and my question is this:
Where can I get some kind of idea what kind of energy savings I can expect? I mean, if two 5-ton 13-seer units are, say, $500/month, what are two 3-ton 14-seer units going to cost? Or two 3-ton 16-seer units? I've googled this, but I can't find a calculator that does what I want.