I have a seven-year-old Fridigaire (Nordyne), 2-1/2 tone heat pump that serves the main floor of my house in north Alabama. It's about 2000 sq. ft. and there is a lot of glass (triple-pane, but glass still). The system is probably 13 SEER (it was a builder's special; not what we paid for; long story). It is an R-22 system and it has a leak, so it is going to have to be replaced soon. I'm planing to get quotes in the spring.

The existing system has always been iffy in heating performance. It starts to struggle at about 27F and is pretty useless at 18F. It has no lockout but I have my home automation system programmed to take it offline (by switching the thermostat mode to emergency heat) at 12F. Cooling performance has been fine. We are on a mountain at an elevation of about 1400', and it tends to be a bit cooler here than in the city center, although it can be warmer in the summer. Humidity is of course insanely high in the summer, and the existing system has done a good job of humidity control.

Winter weather here tends to follow one of two patterns: either the outdoor temp is 35-40F and it's raining, or it's 20-25F and dry. So we really need a system with demand defrost. The Fridigaire uses timed defrost and it often goes on defrost when there is no need, but I can't increase the defrost time because it will ice up in humid weather.

I've been looking at the Trane XL18i and the Carrier Infiniti 16. These are systems around 17 SEER and 9.5 HSPF, which seems to be the optimum configuration for my area. A few considerations: (1) Do these systems have to be used with the manufacturer's supplied thermostats? As I mentioned, I have a home automation system. It controls the setpoints for all three of the house's HVAC systems, and over the years I've developed some pretty sophisticated algorithms for it that manage the setpoints based on outside temperature, what time we're going to be home, and a bunch of other stuff. I don't want an HVAC system that the home automation can't interface with. (2) The local Carrier dealer is also the company that has been servicing my existing systems for the past several years, and I've been happy with their service. I have no experience with the local Trane dealer. (3) I understand that the Carrier Infiniti doesn't really have a proper demand defrost. That's a concern given the two weather extremes I mentioned. (4) I see that the Trane uses a Spine-Fin coil. We have a lot of trees on our lot and a wooded area behind the house. I don't want to have to be constantly picking dead leaves out of the coil.

Any thoughts? I will of course be getting load calcs done as part ot the quotes, and I will be replacing the indoor unit also. Based on other quotes I've seen lately, I'm expecting the price to come in around $8000. I'm thinking about asking the Carrier deal to also quote a Greenspeed system, but I'm not sure it's worth the additional expense for the prevailing weather in my...