you are planning on two systems?

if not you should.

If you post your (nearest big town/city) location, it might help to give a better answer.

Many (most) 2 stage A/Cs operate at about 70% and 100% (Carier might be 50/100) of rated capacity. If your climate typically goes from cold/cool (no A/C needed) to full blown summer, then a single stage would likely do well.
Also, 2 stage units are available in full ton sizes only.

The key, is an accurate heat calc and an assessment of your climatic conditions. For example: if your heat gain is 4 tons, and you go from cold to hot (as above), then little to be gained by 2 stage. If say, you're near the ocean, and have a moderate spring (warm periods, but not oppressive), then a 2 stage might be better. The choice of unit should be based on the rated BTUs at each stage (how it matches up with your heat gain. You definitely don't want to be oversized.

As far as reusing your HP, how has the unit been stored/transported/etc. With your location, you might benefit from higher SEER unit(s).

Good luck. Choose wisely, grasshopper.

V

Ah Tiger, you beat me again.

V

Tigerdunes - Yes I am planning on two systems, the upstairs will use the 3 ton Nutone HP that I already have.

Veesubotee - Nearest big city would be Pensacola, FL. The current HP was disconnected by contractor and is being stored outside uncovered. The air handler is being stored in a storage unit. Lots of humidity here, so I was thinking 2 stage to help with that.

Thanks for the help so far!

for dhuston

these are my minimum specs for a new HP system. 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

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.

I would only use authorized dealers for the various brands that provide quotes. see mfg websites.

I would look at Trane/AmStd,Rheem/Rudd,Carrier/Bryant.

I would not purchase a new HP system that did not have electronic demand defrost.

IMO
Good Luck!

Ditto tiger's last post. Since you'll beed a licensed pro to install anything with refigerant in it you should ask them to complete a Manaul J as well to see "what the book" says a properly sized system. Living in Florida you'll probably see a less than 2 return on investment on a higher SEER model as well