Homeowner here, but I like to think of myself as being somewhat knowledgeable in matters HVAC, so I will address some of your points.

2story 14.5 yr old brick home in ATL

1st flr 1800ft - 2.5t Carrier AC 90K BTU furnace
2nd flr 1800 ft - 2.5t Carrier AC 80K BTU furnace

>I'd like to know how large (square feet) your house is. I suspect they run frequent short cycles.

Gas ~ .99 / therm
Electric - 9.87 cents/kWh

Plan to be in house for 20 years. After ton or reading on this VERY helpful forum, settled on Trane to reduce my options.

>Based on some of your following comments, you shouldn't limit yourself to one brand, but rather try to find the best contractor.

Difficulty finding contractors willing to do load calc. One reputable owner said customer interview, walkthrough, square footage, count of supplies and returns and consideration of 2 story spaces, windows and 20 yrs exp gets him to the same point as load calc. This true??

>While the above factors are important, he may be lucky and guess the right size, or just opt to replace what you already have, but only by doing a heat calc, (along with his 'expertise', can he be sure. Square footage = rule of thumb. Your cooling loads are likely much more than your heating loads. During the hottest days of the summer, do your a/c's run nearly constantly, and is your house comfortable, humidity-wise? Or, are they running frequent, shorter cycles? Also, you need to know what your latent heat gain (humidity) is. Can't do that by walking around.

For 1st flr (system located in unfinished half of basement)
3 ton XLi15 HP on top of XV80 80K BTU

At 100% efficiency, the HP would deliver 36,000 BTUs. Why would an 80K (80%)unit delivering 64,000 BTUs be proposed.

Highly rated installer quoted the above w/ 4ton blower, adding return to finished portion of basement to promote airflow down there, as we rarely use that space or the 3rd HVAC system.

>Are you saying that you have a third a/c serving the basement? These new returns, are there corresponding supplies for the area (are they part of the system that doesn't run?)?

1)Is 4t blower on 3t system good idea? Current is 2.5t

As long as the blower, be it multi speed or variable speed, can be set up to deliver the proper airflow, it's not a problem. Maybe he had one in stock.

2)I Like XV80 for dual fuel flexibility and dont see need for 90%+ since HP should handle most ATL heating days. Thoughts?

>See above.

3)Is XLi16 worth $500 extra? Dealer says 2 stage makes hard to compare apples to apples w/ XLi15. Says 2 stage offers much greater energy savings and humidity control.

>Depending on what your heat loss is, and the size chosen, the HP may not need to run in stage 2. Two stage equipment is for comfort, not energy savings. You still require the same BTUs to heat your house. Likewise, depending on your actual cooling needs, if your HP will run mostly in first stage for air conditioning, it will help in controlling humidity. It is important that a properly matched evaporator coil be chosen. I had considered Trane equipment at one point, but the contractor could not supply detailed info (specs) on sensible and latent capacity of their coils.

Upstairs (system in attic)
3 ton XLi15 HP w/ electric strip backup and variable speed blower

>Same comments apply from above regarding actual heating needs.

1) ATL winters, 2 story foyer and family room, heat rises makes me think I can do w/o gas upstairs.

>With strip heat, you don't need gas.

Will I save much in price on variable blower w/o furnace, or should I get the XV80, even though I do not think I will use much gas up there?

>In order to make these decisions as to what type of equipment (gas or electric)makes sense for you, you need to know what your heat losses and heat gains (sensible and latent) are.

2)XL16i HP worth extra $500?

>Off the top of my head, I would say no. (my guess)

3)Is 4t blower w/ 1 extra return on 3t system good idea? Current is 2.5t

>Generally speaking, more return is good. Has your duct system been evaluated and your total system static pressures been measured?

I am assuming I should insist on Honeywell VisionPRO IAQ for both?

They are an excellent TS and can enhance dehumidification when used with a variable speed blower and combined with other air quality equipment.

Also have been told that XV90i no loger offered by Trane. Is it and if so, should I consider it downstairs?

That is true. Again, you need to know the (heat calc) numbers to accurately determine which fuel makes the most economic sense as your alternate.

Any advice would be appreciated!!

Information about wall and roof insulation, make of windows, shading of house, etc., would be helpful.

V

uga

the XV90 furnace is only available with Trane's Clean Effects combined in the unit-XV90i. still is listed on Trane website-see link below.

the XV80 is available as a standalone as well as a combined unit that includes the Clean Effects.

I think your choice of brands/mdls is good and your strategy of having dual fuel for downstairs only is correct.

you need a load calculation for both heating/cooling performed and broken out by living area/zone.

you should not go up in size on outside condenser without verifying that your ductwork both supply and return is sized correctly and can handle the additional CFMs. if you have any hot/cold spots in your home and/or poor airflo movement, now is the time to address with your dealer.

This is the furnace I would recommend for downstairs depending on load calc.
XV80 TUD080R9V3K 40 17.5 28 64,000/41,600 80(three ton blower)

I agree that a 90+% AFUE eff furnace is probably overkill and unnecessary for your area/climate when paired with a HP. Still, I suggest getting a price on either the 90i or XV95 for comparison purposes.

I would not have the XLi16 condenser.

for the upstairs, I would stick with the best matching var speed air handler. you will get a little residual heat from downstairs plus you get better performance/eff numbers pairing the XL15i HP with correct air handler vs gas furnace. However, dealer will need to check your electric service/breaker panel for circuit/capacity to handle backup heat strips.

as said, earlier, I would not have the XL16i condenser.

The HW VP IAQ stat is your best choice.

you should have some type of whole house air cleaner cabinet for the dual fuel system. I am not a fan of EACs because they can be problematic and most homeowners will not adhere to the cleaning/maintenance schedule. Keep to a 4-5" pleated filter media cabinet.

IMO

Thanks got your replies.
To answer your questions:

Whole house is ~3600ft, split evenly b/t 1st and 2nd floor. 1/2 of 1800ft basement is finished also. Finished portion has ~3yr old HP only. Dealer suggests adding return from 1st floor system to finshed portion of basement since we rarely run the basement unit he says good idea to promote airflow.

Existing AC runs almost constantly when 90+ outside - has trouble maintainig even 78 degrees during day. I am addressing poor insualtion right after HVAC install. Existing gas heat acheives temp, but does cycle 4-5 times per hour.

Have I understood your points correctly?

1) I need to get a load calc done to accurately estimate heating and cooling needs. In terms of what? BTUs, tonnage?

2) XLi15 3t HP downstairs will deliver up to 36K BTUs, so I should ask why is contractor recommending 80K BTU furncace as backup for downstairs. Are you suggesting 3t is too small or 80K too large based on the BTU discrepancy you pointed out.

3) XLi15 3t HP w/o XV80 furnace upstairs is good idea as long as breakerbox has capacity for backup strip heat. It does get in to the teens/20s occaisionally in Atlanta, but I wont have need to supplement HP very often.

4) 4t blower ok for proposed 3t HPs, assuming existing ducts on old 2.5t systems can handle the airflow. Why would dealer want 4t blower?

uga

an observation is that you are borderline undersized in cooling and grossly oversized with heating which explains the obvious shortcycling.

"Finished portion has ~3yr old HP only. Dealer suggests adding return from 1st floor system to finshed portion of basement since we rarely run the basement unit he says good idea to promote airflow."

I do not like that idea at all. Why do this when you have a separate system downstairs that I assume has both supply and return registers. I would not mix basement air with main floor air.

1.a load calculation broken out by each area/zone will give you both the cooling BTUs and heating BTUs for your home allowing one to properly size new HVAC equipment. ask for it in writing.

2.there are always compromises that one faces even in HVAC. assuming you require a three ton HP like the XL15i, you need an air handler or furnace that has a three ton rated blower to move that air. here are three choices with a three ton XV80 furnace all with different BTU output. Keep in mind this is at 80% efficiency. the middle model is probably the size/mdl you require:

TUD060R9V3K 40 17.5 28 48,000/31,200 80
TUD080R9V3K 40 17.5 28 64,000/41,600 80
TUD100R9V3K 40 17.5 28 80,000/52,000 80

3.for upstairs you want to match the XL15i with the best rated var speed air handler to reach the optimum performance/eff numbers.

4.you don't need a furnace with a four ton rated blower as long as the appropriate three ton model is available. and in your case it should be-see list above. but you must be certain that by going up to a three ton HP your existing ductwork is OK. if you have any hot/cold spots in your home, now is the time to address this issue.

"Why would dealer want 4t blower?" I have no idea. I would like to hear his explanation.

IMO

Down to the final configuration:

I don't have the load calc in front of me, but rough numbers were:

Main Floor
Total Heat Gain - 36000BTU
Total Heat Loss - 41000BTU

Quoted:
3.5t XL15i HP 4TWX5042A1, 3.5t coil 4TXCC044BC3, 80%4t furnace *UD080R9V4
ARI.org shows:
42000 cooling
11.60 EER
14.00 SEER
43500 Hi Heat
8.00 HSPF
28400 Low Heat

2nd Floor
Total Heat Gain - 24000 BTU
Total Heat Loss - 28000 BTU
3t XL15i HP 4TWX5036A1, 3.5t coil 4TXCC044BC3, 80%4t furnace *UD080R9V4

ARI.org shows:
36800 cooling
12 EER
14.5 SEER
34400 Hi Heat
8.2 HSPF
22600 Low Heat

I think the reason for the 4t blower was that the larger cabinet size allows a larger coil (the numbers do look much better).

Any problems with these setups?

HP only w/ elec heat not an option in attic ($$ to run power)

A little disappointed with less than 15 seer - maybe I put too much stock in the maketing slicks...

Sounds like consensus is that XL16i not worth the extra $500.

Any sense looking at XL19i? I will be in this house forever, but as far as I can tell 19i is only available in R22.

I would keep the XL15i's unless you were looking at the high end XL20i units.

With those numbers it would seem as if the dealer was oversizing the systems:

- If the heat loss was 41k btu, even the 60k 80% furnace would put out 48k btu. The 3.5 ton may be needed to match the sensible heat gain requirement.

- 24k btu is 2 tons. I wouldn't think you'd need more than 2.5 tons. 2.5 tons may be a better option to meet the sensible gain. You'll want to ask for the reasoning behind your dealer's selections. The 80k upstairs is especially surprising.

I'd be more disappointed with the low 8/8.2 HSPF ratings on the heat pumps.