We have a rental house that's 850 square feet in Riverside County (about 1 hour west of Palm Springs). Summers are hot and very dry. The house is a box, single story, 2 BR/1BA, south facing.
Built in 1952, the house needs a full AC unit and we'll replace the furnace at the same time. A manual J was not performed by any of the contractors who gave us estimates. In addition to the new AC/furnace, we'll change out the last two windows (to vinyl, double pane) plus new insulation in the attic.
Question 1: shall we buy the two-stage? (adding $ and 14.5 SEER upgrade from 13) Or with this small a house and completed upgrades, shall we go with the single stage?
Question 2: is "single-stage" / "two-stage" an option that refers to the furnace or the air conditioner? I seem to have seen it both ways in blogs, etc.
In case more details are needed, here are the systems the HVAC contractor put together:
TEMPSTAR/CARRIER systems (both)
Single stage system:
Single stage furnace - model: MSL451412A. A 2 Ton capacity horizontal heater. 80% AFUE
Evaporator - coil model: ENH4X24L17A.
Condenser - model: N4A324AKB. 2 Ton. 410-A. 13 SEER efficiency.
Two stage, higher efficiency system:
2 stage variable speed furnace, 80% efficiency.
Evaporator coil - model: ENH4X24L17A (used in both systems)
Condenser - model: NXA624GKA (16 SEER)
This match will produce 14.5 SEER efficiency