1. Is there a big difference between an American Standard unit and a Grandeair (and who makes the latter?)
2. In a beach community, do aluminum or copper coils make more sense? (opinion appears to be divided on which is better).
These are HPs?
I Believe that Trane/AmStd systems hold up better in a harsh coastal environments.
Grandeair is not Am Standard.
these are the minimum specs you should be looking for.
both outside and inside units should be replaced to have a properly matched system.
15 SEER, 12.5+ EER, 9 HSPF
best matching VS air handler
full BTUs in both cooling and heating for your rated size
R-410a refrigerant(same as Puron)
scroll compressor preferred
electronic demand defrost preferred
thermostat with "dehumidify on demand" feature
staged backup heat strips
new and correctly sized refrigerant lineset
10 yr warranty on parts and compressor
you want a thorough inspection of your ductwork system. size, overall condition, supply and return lines, insulation qualities, leak test, etc.
any hot/cold spot issues in your home should be addressed.
My personal recommendation is Trane/AmStd, Rudd/Rheem, and Carrier/Bryant.
Depending on your location, I would not purchase a new system that did not have electronic demand defrost.