Well shaded, masonry ranch house. Can I undersize my AC?
We've been asked to choose between a 13 and 16 seer unit for our AC. We've already picked a 96% efficiency furnace, and are now debating going with the higher efficient AC set up as well.
Of course I know nothing of the difference except Barack Obama might give me some money if I buy the more expensive unit (only about $600 more) but I'm not positive we'll get a return on that investment.
We live in Milwaukee. House is a 2000sf 1940s stone ranch with 8 foot ceilings and a full basement with open stairway leading down. We're doing an entire system swap, previously had radiant heat in the ceilings (that's another story) so there's a ton of insulation in the attic. Currently has no AC except a 1-ton window unit in the middle of the house which seems to keep it relatively comfortable when its running but I've also noticed it's not bad when its off either (house is vacant right now and undergoing renovation - I turn on the AC when the humidity gets too high). We have an average number of windows, but they're all large, including three 9-foot sliding glass patio doors. The house is relatively shaded throughout the day.
TL:DR 2000sf stone house has been getting away with a 1-ton window unit for the past 50 years. Can I get away with a 13 seer unit? Are the cost savings worthwhile for a more efficient unit?