Heat pumps are sold as a matched set. If you use your old indoor unit
over, it's like putting a chevy engine in a ford truck with a toyota
transmission and a dodge rear end. Nothing matches up. It may run but
it won't work right.
Get a new load calculation done. Measure the existing air flow with a
flow hood or other accurate instrument, NOT a "HAND_O_METER". Make
proper duct modifications as necessary to install new indoor unit.
Make sure Freon lines are sized right. Make sure power wiring and
breakers are correct.
Ask the contractor about SEER & HSPF (SEER is cooling efficiency, HSPF
is heating efficiency)
Ask about load calculation for proper sizing, NOT 500 or 600 square
foot per ton. If he just measures square feet of floor area, FIRE
HIM!! Then get a new contractor.
Ask if you have proper air flow and have him measure it with accurate
instruments. If he just uses his hand and says he has experience doing
that, FIRE HIM!!, then get a new contractor.
Ask about scroll compressors.
Ask if his techs are NATE certified.
Ask about Variable Speed Blowers for better humidity control (Set to
Ask about two stage compressors. (Lennox has two stage Copeland Scroll
with 18.6 SEER efficiency!!)
How high an efficiency you want depends on your local electric rates,
the size of the load and your local climate. Unless you have very
cheap electricity or very mild climate, you want at least 13 SEER
(Which will be low end next year!).