I know what you mean. I fault the lax building codes. I asked the builder if I could pay for:
1. Upgraded windows
2. Tyvek wrapping on the house
3. The best caulk money can buy
I was told no each time or that the price they would quote would make me say no.
So I have spent time installing v strip and upgraded weather stripping on the windows and doors and went so far as to remove the window casing and add spray foam on the worst windows. All exterior facing outlets have the insulation covers.
One of the contractors thinks they installed an undersized furnace at 64,000 BTU. He claimed he services the same model house up the street and theirs is bigger. It has some credibility, as on cold windy days, the furnace doesn’t shut down. I also don’t set back the temperature at night since it takes 3 hours to warm up again in the morning. I get lots of air flow from the vents though.
The existing condensers were dropped on the ground on pads and were far from level. I built frames of 2x4 pressure treated lumber to level them off.
I could roll the dice and what until the AC fails and replace it during the summer at the going rate with no rebates or tax credits. I would only buy a mid grade replacement in this scenario and keep the 64,000 BTU single speed 80% furnance. It could go this year or last 5 to 8 years more. Who knows? We just seem to get couple more each year fail on the street.
The other option is to replace with a modulating 95% variable speed furnace with a high efficiency two-stage AC unit, intelligent controller and take advantage of rebates and tax credits. This option would cost me about 1.5 times (after rebates and credits) of a mid level replacement AC unit.
I agree that I would only save about $400 to $500 a year on energy. But since I am convinced the AC will fail during my stay here, I am leaning towards spending 1.5 times now and saving the $500 per year and enjoying the improved comfort.
I need to find some experts to look at the duct work and calculate the load properly.