If the A/C (heat pump) in the house in question is said to be 3 years old, that certainly could be. The outdoor unit (which contains the compressor) very well may have been replaced three years ago. A proper replacement would also have involved the indoor coils so that the system is a "matched set" ... but that isn't always done. Or is there perhaps a completely separate blower and duct system for the heat pump, and the "old" 1979 furnace is no longer used at all? ALL air conditioners are heat pumps, technically. They "pump" heat from one place to another. In the case of air conditioning (or a heat pump in cooling mode), heat is moved ("pumped") from inside the house to outside. The hot air blowing from the outside part of the system (the condensor) is that heat (mostly, not quite all, but no need to get into those details). In heating mode, the system "reverses" and moves ("pumps") heat from outside to inside. The inside part of the system blows warm air, the outside blows cold air. Basically, it's cooling the outdoors. :-) There is heat in the air down to absolute zero when all molecular motion stops. All heat pumps must have an auxiliary or supplemental source of heat, which comes into play when outdoor temps drop into the freezing range or lower, at which point it gets harder for the heat pump to get enough heat to maintain a comfortable indoor temperature. Just like the coils in a freezer get iced-over, the outdoor coils on a heat pump (which as I said above are essentially air conditioning the outdoors) get iced-over and must be defrosted. When a defrost cycle triggers, the system turns back to cooling mode for a few minutes so the outside coils heat up and melt off the frost. The supplemental heat (typically an electric furnace) activates to heat the cool air that would normally be blowing inside the house. So yes, the "heat pump" is in the unit outside, but there must also be a "furnace" that is part of the system.

ryanhughes, The Trane setup with 80% 2-stage Var and 13 SEER, plus indoor cased coil, new thermostat, equipment pad, 4" media filter and labor comes out to $6077. The Goodman setup with 95% 2-stage Var and 16 SEER, plus Cased Indoor coil, new thermostat, equipment pad, 16x25 MERV 11 Air filter and labor comes out to $6098. (Special friend discount) The EverRest setup, which I am not considering anymore. 80% 2-stage no variable speed and 13 SEER, plus coil, thermostat, CAP-100 filter and labor is $6957. TRANE vs Goodman. Trane probably has a better reputation, but in my scenario I may go with the higher efficient Goodman. I'm not 100% sure yet, but definitely getting there.

garyg: These are the figures that led me to switch my buying preference from an Infinity 19 to a 16. The second ARI reference is for the Infinity 19. One would think that because one is a "19" and the other a "16" that the SEER for the 19 would be a lot higher. But it's actually 0.1 lower, at 14.4 compared with 14.5. I wonder how many people are mistakenly thinking they are buying a much more efficient unit than they really are (especially with the 5-ton units). I think the industry ought to require manufacturers to make their literature clearer in this respect, instead of referring to unattainable figures (or ones that are only achievable with a certain furnace and HP or AC tonnage). So given no real advantage to the Infinity 19 over the Infinity 16 that I can tell with my configuration, I'm going to choose the lower-priced Infinity 16 (a little lower EER but higher cooling capacity).

what location? what size home? what size existing furnace and AC? and yes, those performance/efficiency numbers on HPs do matter as far as operating costs. While not a fan of Lennox HPs, it should be said that Trane makes very good heat pumps but they are behind the curve in efficiency numbers in dual fuel applications as indicated in your post,especially HSPF. you also need to look at BTU rating for 45 degree and 17 degree as listed in AHRI HP Directory. The Trane furnace is two stg 95% eff while the Lennox is two stg 80% efficient. Big difference there. what thermostats were quoted? what about an air filter cabinet. both important. IMO