I know the general rule is that you don't install a 2-stage AC with a single-stage furnace, but everything I read seems to point to humidity issues with this setup. Here's my situation:
I live in the Seattle area and am looking to install central AC so we can keep the house closed up most of the time due to health reasons in the family. The summer climate here is exceptionally mild with average highs of 75 degrees and humidity levels of around %50. The house is four years old, is reasonably well built and very tight. The existing furnace is an 80% single-stage Bryant that's more than fine for our mild winter temps (our highest winter gas bill has been $150 including water heating). Replacing the furnace at this point makes no sense economically.
I've now had two bids that suggest getting a 2-stage AC to pair with my furnace. The vast majority of the time this would run at the lower setting, extending runtime and improving air circulation throughout the house, which is an issue at 75 degrees. Both companies say they do this on a regular basis when a customer needs to run the AC througout the summer. Only on the handful of 85 degree days (<10) we get every summer would the second stage kick in. Major humidity control doesn't appear to be much of a concern during the summer.
What do you guys think? Will this cause me any major problems?