Ok, here are my thoughts:

1. Trane is good equipment, and I do recommend it. But please don't purchase it hoping for it to last as long as your old unit did. They just don't make them to way they used to. Trane units will have 10 year parts warranty, as will most brands, so that provides some reassurance. Really, most equipment is similar today in terms of components. I like the aluminum outdoor coils of Trane, especially if from what I gather from your post you are on the coastline. But then again, I don't here of copper outdoor coils leaking often. I don't like copper coils inside but that's what all brands use, even Trane in some of their coils.

2. It's good that you're getting all new ductwork. You want a dealer who will size and design the ductwork properly, and the same goes for the unit itself.

3. I do not like the Trane XL16i. It's low stage capacity is around 80% of full capacity, so for the price increase I don't see much of a difference. Plus latent capacity (humidity removal) of the 16i on low isn't all that great. I read at one point that the single stage 15i is better at dehumidifying than the 16i on low. If you want Trane and 2-stage, I'd say go with the XL20i. But I wouldn't discount a single-stage unit.

4. Trane is coming out with some new units soon (thankfully). They are supposedly going to have a new 16 SEER 2-stage outdoor unit, hopefully with some improvements made, sometime before the end of this year. Same with the indoor air handler--supposed to be smaller in physical footprint and (I haven't confirmed this) use an aluminum coil. I look forward to these models.

5. Cost for 2-stage equipment is generally high. With new ductwork, might be looking in the $8-10,000 range. Single stage units will usually cost around $1000 less upfront cost, but not always. Really depends on the dealer. And the CleanEffects filter generally costs $9-1100 installed.

The big issue with Trane is the XL16i.
unfortunately it's got a bad reputation,

If you want 2 speed condenser right now, I prefer the carrier or bryant 2 speed condensers they are impressive to me. The non communicating 2 speed is a very good value Bryant 226A. You can go up to the Carrier Infinity or Bryant Evolution for data control or Trane's XL20i.

Trane does make a very good quality single speed condenser
XR15 same as the American Standard Heritage 15.

I would not put your air handler in the attic it will cut the life span do to the attic conditions. I try and get people to move their systems if the air handler is in the attic.
Trane is creating a seal tight foam insulated air handler, it's not out yet. This I am looking forward too, since I'm also in the southern region and would be more suitable for attic and garage installs in the southern region.

For price, we can't guess, the little things add up. It's just not the equipment, you purchase equipment with a quality installation and a company that will meet your customer service expectations since it shouldn't end after the install.
First priority - A/C Contractor
That is what you need to find! Don't worry about the equipment that is secondary.

if you are going to replace duct do it now, we are getting into hotter weather and when it's hot it will cost much more.

crazy

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 not have either the XL16i or AmStd counterpart Heritage 16.

I would stick with the XL15i or XR15. I would also look at the AmStd Heritage 15.

I am not a fan of two stg equipment because of added upfront cost and marginal improvement in comfort and operating cost.

Look at the PerfectFit media cabinet over the CleanEffects.

IMO
Good Luck!

Classicdave,

I know we discussed this earlier, but are you any more certain based on your knowledge and info from your distributor whether the new air handler uses an all-aluminum coil?

Thanks for your info. Perhaps info on this new model is limited at the moment.

Ryan,
Yes Trane plans to use an all aluminum evaporator coil. Made from pure aluminum. Because of the process Trane is implementing, The aluminum coils now have to be made at a different plant do to safety issues. I guess there are explosive issues that can arise from the aluminum process mixing with the process they are using to make their other products.
I believe from my rep Trane is doing something to revamp their plant so that they can make the aluminum coils at their regular site but I'm not sure on this.

Hey classicdave, tigerdunes, ryanhughes, etc.. steering now toward the bryant brand over trane.Had the open-cell foam blown under roof for envelope, all new windows and doors meet <.30 on both scales and rebate went with that.>1. Bryant: 226ANA,FV4BNF002TOO,T6-PRH01-A,FB4-5
2. 286BNA024, FEANF003T,SYSTXBBUD01-B,KFCEH2901N09
3. 265ANA,FV4BNF002TOO,T6-PRH01-A, same filter FNCCABBB0014
4. Trane: XR15, var speed,programmable
5. why not the XL15i
Bryant says only need 2 ton size(on coast of Hilton Head SC)
Any thoughts? Thanks for info.

Ok what about the most important part.....proper sizing. In 23 years has the home been updated? New windows, doors added insulation? Yes so why another 3 ton unit. Seem large for a 1725 sq ft home. I live in PA and have about a 2800 sq ft home built in 1978. Updated the southern exposure windows only. New 3 yr old HP is a Rheam 3 ton. Works great. Lowered fuel bills by about 30%. The point is not brand name but size to size of home. Electric strip hardly ever comes on except in defrost. I even disconnected one of three strips of electric heat two years ago. The only marginal time I had in heating was two years ago the temp hit 4º but 2800 sq ft home heated with 3 ton and two of the three strips of electric. Highest electric bill $231 which was the January it hit 4º. Proper sizing best for de-humidifing also.

crazy

what size is existing system?

several thoughts come to mind.

I want to see the load calculations in writing on the software letterhead. if you have not had this done, insist on it. you need to tred carefully when you make these superduper insulation upgrades as far as sizing new HVAC.

many people on these forums do not understand summer weather in a Southeast location, much less one in a coastal environment. My point is that I don't want to be borderline sized correct for HH,SC.

I like Bryant equipment If you elect to go in that direction, insist on "T" tin plated coil. I am not a particular fan of two stg condensers because of cost and marginal if any improvement in comfort and operating cost.

While you will usually pay more for Trane, I do believe that they are more reliable and last longer in a coastal environment. My choices would be Trane's XL15i or XR15 and AmStandard's Heritage 15.

IMO
Good Luck!

The summers are brutal here. My 23yr Trane is 2.5 ton. Not sure that manual J was done by anyone. The Bryant guy says to put returns in each bedroom (have only main one now), the trane guy didn't mention that. Also, one guy is not with a "company", he's an individual contractor. Cheaper, but what if there's a problem, and how does warranty fit in? Is it still a no for air handler in attic since I have the foam envelope? I'm open to all advice. Thanks guys.

I would not go down in size until I see the numbers in writing. guessing is never a good idea. More returns yield better airflow and comfort. certainly adding returns will help. returns have nothing to do with correct overall system sizing. discuss air handler location with dealers. where is ductwork located? where is current air handler located? I would only do business with authorized dealers. Because of your location, I would lean toward Trane or AS.

IMO

Tigerdunes,
Air handler is in closet in hallway, ductwork in attic. Having all new ductwork installed there. HVAC guys recommend closet where it is. I'll contact dealers for the manual J. I thought I would need 2-stage heat pump for this area because of humidity and heat, but it seems that isn't the case. What is the difference between the XR15 and XL15i? I was reading Donna from NC's post and you guys recommended Honeywell instead of 803 thermostat to better control the humidity, does that apply here also? Thanks for all the info. I hope this is the final leg of my journey on this remodeling. I've been sitting way too much in front of this computer. LOL. Nadine

The XR15/XL15i are nearly identical performance wise. The 15i has a nicer top to keep leafs out, is a little quieter (with different fan motor), and has 2 more years on the compressor warranty (when registered). In other words, not a big difference between the two. If price increase isn't significant, the XL15i is a nice choice, but the XR15 is the popular 15 SEER unit with Trane right now since I'm sure it costs a bit less.

The Honeywell stat is nice (called the VisionPRO IAQ) IF your dealer knows what they're doing with it. It's not set up like a conventional thermostat. It's worth mentioning. If not the 803 will be fine. For the Bryant systems you'd use the Evolution control, so the Honeywell doesn't apply in this case.