Before proceeding with replacement, get a load calculation done to determine proper sizing. Did the old 3 ton short cycle or run long cycles? Sounds like a lot for 550 sqft., but you mention a loft and high ceilings. A load calc will tell for sure.

Brand won't matter as much as having a proper installation. Trane makes good equipment, although I don't think very highly of the 16i based on what I read (low stage capacity around 80% of high stage, so not a very noticeable difference; poor dehumdiification in low stage; etc.).

cjb56houtx

you do need load calc. These are heat pumps? I would not have the Trane XL16i or AS Heritage 16 either AC or HPs. poor performance/dehumidification.

I would stay with a properly sized high eff single stage HP.

I think a two stg is overkill for a TH with such a small living area regardless of the high ceilings.

my personal favorites are Carrier's Performance 15 "H" mdl(or sister company's Bryant Preferred 15 "H" mdl) as well as Trane's XL15i(or sister company AmStd Heritage 15) with best matching var speed air handler. all of these HPs qualify for the tax credit.

IMO
Good Luck!

Thank you for the feedback.. FYI - These are not heat Pumps - Strictly straight A/C units w heat strips. The old unit ran fine in its earlier years and in its later years was nursed along and did not cool as well. I believe 3 tons will work fine as the old unit did the job in the early years and had to work in the summer when the sun came in during the late PM in the later years. There is a lot of heat that scomes through those windows in the summer. The efficiencies in todays units probably deliver much better cooling than I was getting.. Especially if they are sealed. I do have a second unit taking care of the living quarters and the Den area which are alongside this main room - when I sealed the unit 2 yrs ago - what a difference..
Another proposal came in today with 2 different A/C units w strips and 2 different Heat Pump quotes from the current Lennox servce provider who services the equipment.

1. Lennox XC14-036 Condenser unit (14.20 SEER/12.00 EER) using the new 410A refrigerant
· Lennox CBX26UH36 Fan Coil with Thermostatic Expansion Valve
· Lennox ECB26-10CB Heat Strip with circuit breaker
· Manufactures warranty Condenser 10 year compressor & 10 year parts, Fan Coil 10 year - $6986.00 Installed w existing Thermostat

2.· Amana ASX14-036 Condenser unit (13.50 SEER/11.80 EER) using the new 410A refrigerant
· Amana ARPF363616 Fan Coil with Flow-rater Valve
· Amana HKR-10C Heat Strip with circuit breaker
· Manufactures warranty Condenser Life Time compressor & 10 year parts, Fan Coil 10 year
$7080.00 Installed

3. · Amana ASZ14-036 Heat Pump unit (15.00 SEER/13.00 EER) using the new 410A refrigerant
· Amana ASPF303616 Fan Coil with Flow-rater Valve
· Amana HKR-10C Heat Strip with circuit breaker
· Manufactures warranty Condenser Life Time compressor & 10 year parts, Fan Coil 10 year
$8168 installed - and qualifies for Tax credit

4. · Amana ASZ16-036 2- Stage Heat Pump unit (16.00 SEER/12.50 EER) using the new 410A refrigerant
· Amana AEPF30361A Fan Coil with Flow-rater Valve
· Amana HKR-10C Heat Strip with circuit breaker
· Manufactures warranty Condenser Life Time compressor & 10 year parts, Fan Coil 10 year
$ 9,442.00 Installed

SEERs look a little low compared to the earlier quotes.. I am not familiar w Heat pumps only straight A/c and Heat strip units.. I feel that running that compressor unit in the winter just creates wear..That is why I'm slanted toward heat strips.

Can one get a manual J from an independent source or does it have to be a contractor? I hear they are some work to work up and obviously I will pay for it. How much are they.

If you have suggestions on specific units / condensor / air handler combinations I'd be happy to check them out as well. This is a big expense and i want to do this right. Thanks

The Amana units should not cost more than the Lennox units. Possible mark-up due to tax credit qualification? Also, I recommend a variable speed air handler with whichever setup you go with. For Lennox, it's the CBX32MV. Carrier and Trane should have multiple systems in the 3 ton size that meet the tax credit requirements with the variable speed air handler.

A competent dealer will be willing to do a load calc. Ask first, before offering to pay for one. You can run your own (search Google for HVAC-Calc if you know all home insulation, windows, etc.). Ideally it's part of the replacement and the company's obligation to get the sizing right. While it does sound oversized (especially if it's a second unit, if I understand what you're saying correctly), you do mention that it always did the job well, keeping humidity reasonable and not short cycling on hot days.

I'll see what I can do to get a load Calc done. I know this TH like the back of my hand as I have been working on it for 20 years and moved into a unit that needed a lot of work just to inhabit. I know the insulation etc...

Saw some software yesterday on the web. Do you know of any free software for a calc?? Looks like about $50 to use one..

Also what is your definition of short cycling. (on ___minutes and off___ minutes. Would like to fully understand what that looks like. Thanks

A properly sized unit should run near constantly on the hottest "design temp" days. HVAC-Calc is a good program to do a load calc with, and it costs around $50 to use.

and a heat pump will give you a good savings in our mild winters. within 2 years in my area (La.) heat pump upgrade cost from electric strip pays for itself.

you need to realize that when you change your windows and reduce the heat gain that 3 tons is hugely oversized for 500 sq ft.

imo you should have load calc done by independent rather than hvac company once you provide info for correct inputs in to load calc. then you can use the load calc to shop contractors. load calcs are only as accurate as the info
entered into them.

visit www.hvac-talk if you have a chance and post your concerns there. there are houston companies that participate in their fourm.

best of luck.

cj:
seems we are doing the same task. I, too, am getting bids for central ac top floor replacement. Downstairs central unit is currently fine. I have also started to get window replacement bids. I, too, have downstairs cathedral ceiling with loft exposure for upstairs. Older unit, per one contractor, said attic unit read 3ton. He quoted on a Rudd or America Standard, my choice, same price. He will replace entire system and replace all attic duct work on both downstairs & upstairs for $5400. This is for the 14seer R410.
I have also checked the various hvac specs and CR & the 5% variance between best and worst reliablity is much to small to concern about brands. I have learned to focus on Aspen coil.

OK - I bought and used the HVAC-Calc program to calculate the load demand on the unit . Is it possible that the old unit was so oversized? Obviously not working efficiently in the end.. I have replaced a major amount of window space in this area with Double paned-Low E-Argon filled vinyl units and the doors as well. The program is telling me that I have a need for a 2 ton unit. Can that Be? Go from 3 ton to a 2? With the Cap & Trade/(Tax) bill in Congeress and the possibility of the bill passing I'm told electricity rates could double / triple. Houston has the highest electric rates in Texas as it is. I'm not interested in running this system all the time. When I'm not here the system is off or set at a high temp.

In another sting in these postings it was suggested the following units for a Miami installation. Since houston is like Miami in many ways could you moidify these so I can get updated quotes.

1. Lets say we go to a 2.5 ton unit.

1. Trane XL20i
4TTZ0036A1000A
4TEE3C04A1000A
BAYHTR1410PDC
TCONT900AC43UA

2. Trane XL15i
4TTX5036A1000A
4TEE3F39A1000A
BAYHTR1410PDC
(Honeywell model #YTH9421C1002)

R410 Refrigerant
NEW refrigerant Line sets required
Variable Speed Air Handler a MUST!
Tin Plate coil
321 compressor saver ?
Ice 22

3. 3 Ton Amana R-410 System 16 seer System
2 speed compressor ASX16036 - $4613
Air Handler ARUF364216 w 10KW Heat strip- $3267
No thermostat included

4.Lennox XC14-036 Condenser unit (14.20 SEER/12.00 EER) using the new 410A refrigerant
· Lennox CBX26UH36 Fan Coil with Thermostatic Expansion Valve
· Lennox ECB26-10CB Heat Strip with circuit breaker

I'd like to have a good decent air handler as the Lennox quote above is the low end lennox AH unit. (MY interptrtation. Dont understand that.
What can you suggest regarding modifications to the above quoted units and I'll get to work on getting these quoted updated. I do not need the Tax Credit.. I'll be using that on the windows.

I am open for other sugested systems as well. including T-Stats and the possibility of a heat Pump unit instead of straight A/C and heat strips. Thanks.

Any feedback?

Would appreciate comments on 1-4 above (or other suggestions) if downsized to a 2 or 2.5 ton unit.. Thanks

Apologize for the mis-spelling. 'Sting" should be "string". My word processing program has not been re-loaded on my hard drive.