Cas

How old is downstairs system?

I see no urgency on replacing upstairs system especially since it serves a living area that is not used often. If you haven't done this already, you should a good PM/checkup performed on the upstairs system.

I find the Rheem quote on the high side. I don't recommend going up in size unless ductwork has been thoroughly checked especially on size both supply and return to see if it can handle the additional CFMs.

Obviously correct sizing is important. If you are unsure, then request a load calculation or even perform it yourself for a nominal fee online.

there are three equally important components-quality HVAC, the install by dealer, and probably the most overlooked and disregarded is the ductwork system.

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 line set

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.

Depending on your location, I would not purchase a new HP system that did not have electronic demand defrost. Carrier does not.

IMO

Thanks for all the info.... A lot to look at and some good questions to ask as we decide if/how we proceed.

There are actually 2 downstairs systems. One 4 ton Carrier 13 seer was installed in March 2011 and is louder than you can imagine. We are working with the local company who installed it to see if there is something wrong. The second system is a 2002 and seems to work fine.

All the systems were checked out pretty well in Sept 2011 by the previous owner and then again when we bought the house in February. We are not inclined to replace the two downstairs systems but thought that a 20 year old system upstairs, even though it's working, could be a lot more efficient and save money in the long run.

Cas

My point on the upstairs system is this. If it is working correctly both heating and cooling and upstairs living area is used sporadically, then what is the point.

Now if family members were living there regularly, that would be a different consideration. If you have the money to spend, then go ahead. If though you wait and have a breakdown, then it's likely you would only be without 2-3 days especially if you have already made a plan for a future replacement system. It's my idea that a nice system HP system should be no more than $2500/ton even with a var speed air handler. I would shop around a little bit more and look at Trane XR15 and AmStd Heritage 15. Definitely though have ductwork looked at if you plan on going up in size. Also you want a new refrigerant lineset.

IMO

Before you do anything about the upstairs systems, make sure that your knee wall insulation is up to standard.

No need to rush into this. If the upstairs system failed tomorrow, you still have two units to keep you comfortable during the day. I suggest going through a summer to see how all three units perform.

Investigate why the Carrier contractor wants to redo the duct work. He may have a legitimate reason. You will be wasting money on new equipment if you have duct issues.

All the major brands have low, middle, and high end equipment. If noise is important, then stick with the middle and high end offerings. They tend to have better sound insulation. You will not see much difference in savings between a 15 and 16 SEER rated unit. I would not let this be a deciding factor in choosing a brand or model.

Yea, the best way to see how well the systems work is to live with them through a heating and a cooling season. Unless you have some other reason to rush, don't. There may be a government or utility rebate available for fixing leaky ducts.

Your prices are high for Rheem in my opinion for your area unless you happen to be in a high end Atlanta suburb.

The point about this being marginally used space is a good one. I'd leave it alone. 16 Seer would never be worth it. Neither would 2 stage or variable speed (unless you have a lot of money). I'm surprised anyone makes a 1.5 ton 2 stage so they are going to give you a 2 ton unit.

Ductwork in the attic installed in 1992 is probably pretty bad and should be replaced. But again, the frequency of use is a big issue.

As far as the noise, make sure you have a programmable stat and shut that unit off at night. The only reason to run the units most of the time is for humidity control and they can do that during the day.

Ditto the knee wall comment. Usually in that vintage house in my area, we see exposed batts in the attic. Cover that with rigid foam for some air sealing and better R-value. Fiberglass is nearly worthless if air can pass through it so most codes now require that fiberglass to be covered in some manner. You can do OSB but the foam gives you some r-value and isn't expensive.