What size AC is there now as well as furnace and it's efficiency?

It has the original HVAC which was installed in 1987. it's 3.5 ton. The new unit I am interested in is 18.5 SEER High Efficiency Air Conditioner and 2-Stage Gas Fired 98% Variable Speed Drive Furnace.

Get a load calculation performed...I would think you would be fine for a 4 ton 2 stage AC condenser paired with 80 KBTU high eff 2 stage or mod furnace. Of course with correct thermostat and pleated filter media cabinet. Ductwork should be inspected and any hot/cold spots should be pointed out to dealer for suggestions to improve. What size furnace and eff do you have now?

IMO

House is very well insulated (as per home inspector). North West Facing (no too much heat come in during the hot peak hours). Installer is going to redo the return air for better efficiency (don't know what that means). Relocating the thermostat from close to the main entrance door to back of the house away from direct impact of sun or outside cold air. Installing Nest 3rd Generation thermostat, Air cleaner and whole home humidifier. Installer suggested 80 KBTU high eff mod furnace, and 3 ton 18.5 SEER High Efficiency Air Conditioner.

Totally opposed to these lifestyle thermostats like the NEST!

Why is that?

I am in central NJ and a live in a 1980's house a little larger than yours. I am skeptical that a 3 ton AC is going to be sufficient. Not sure what "well insulated" means. You probably have R11 insulation in the walls, and R30 in the attic. That was considered good in the 1980's, but barely meets today's guidelines. Have the windows been replaced? If so do you know the brand and model?

I also think a 18.5 SEER AC is over kill for the Philadelphia area. The return on investment going from a 15-16 SEER to 18.5 SEER is very long. I don't believe you need to spend money on an electronic air cleaner. If the windows are tight you should not need a humidifier. You can always add it later if you feel the house is too dry.

No, the windows have not been replaced. It's something on the to-do list. There wasn't much price difference in 16 & 18.5 SEER so I picked the higher SEER. I used some online tools to figure out the investment return and it makes sense to invest on high efficient furnace than higher SEER air conditioning. Thank you for your suggestion about the air cleaner and humidifier.

Thank you for the honest opinion. What kind of thermostat do you suggest? I do prefer something with the wifi capability.

depends on what system are you looking at...