the pic is of one of the existing systems?

this is 4 ton.
keep calling hvac companies until someone
does a Load Calculation.
inspection of ductwork should be included.

3.5 to 5 tons are the bids to date, and it is
just a wag until someone calculates your needs.

insulation in the attic is a good thing..but depth matters,
same with double pane windows, frame & glass type
effects performance.

load calc should include accurate inputs of insulation,
window types, amount of shade and lots of other info.

rule of thumb sizing ( usually 500 sq ft per ton)
leads to oversized hvac systems that run for short
periods of time. this results in high relative humidity,
high operating costs & shortened life of system.

keep shopping until you get someone who does
more than size by sq ft.

best of luck.

thank you for your answer.
Yes, the pic if of one of my York systems. I have 2 like that.
I'll keep looking for a load calculation, unfortunately nobody did nor wanted to do one till now.
In case I really need a 4 Ton, which quoted system is the best balanced one?
If my need is 4 Ton and I get a 2 stage compressor that apparently runs longer but at 60-70% for 75% of time, do I still need a 4 Ton?
In this case I'll have 2.4/2.8 Ton 75% of the time, in theory. Is this correct or how should the two stage compressor be sized compared to a single stage one?
How do you know if the system qualifies for the Tax credit?
How many BTUs do I need to keep the house at real 75/77? Which quoted system will provide more heating (we like it warm in winter)?
thank you!!

Eight Ton for 3700-sf is only 462.5-sf per ton; that appears to be considerably oversized for a 2002 house in Dallas TX.

Have the Home energy Efficiency audit performed, then the cost-effective retro-work, followed up by a load-calc.

When properly installed with an efficient duct system; the first floor should normally get-by with less than 4-Ton.

Here is a link that might be useful: Free Online Whole House Load-Calc

You purchase a 2-stage unit based on the larger size. That is, a 4-ton unit that runs 50/50 (not many do) would be purchased based on the 4 ton size, not the 2 ton size.

The advantage of the 2-stage is that it will run at the lower level (less electricity) during those times you don't need so much cooling. With a smarter thermostat, the tstat will determine when you need to shift into the higher speed (shifts based on needed load rather than just a timer).

As to the size of the furnace, the model number should determine that. That and a load analysis. The fact that you keep it warm in winter should be factored into the analysis.

Do you use NG or propane? What is the rate?

thanks again for your answers!
I have NG, PGF 0.6764, usage charge 0.19771.
Udarrell, what do you mean with retro-work? New/better insulation, new windows..?

For a 4 Ton, which system is the best balanced one (AC, coil, furnace, filter, Thermostat)? If you wanted a well balanced system able to provide all the heat you like, which quote would you choose? Unfortunately I could ony find the installation manual of the heater (all position autmatic ignition furnaces, G8C / FG8 series model , 50-125 MBH input, by York), not the model nr.....
What about the low CADR of the filter, is this a problem as I think or a typo on the Lennox page?

You certainly don't require a 100 K size furnace even at 80% for downstairs system. Look at the 80 K model XV80 with 4 ton rated blower. Add either the XR16 or XR17 in 4 ton size. Both should be eligible for Fed Tax Credit. You also want the 803 thermostat, not the 802. I would also recommend the Perfect Fit Trane filter media cabinet.

See below.

5996439 Active Systems XR17 TRANE 4TTR7048A1 4TXCD063BC3 1370 1095 *UD2C080B9V4 50000 13.00 18.00 1 RCU-A-CB 336 Yes

IMO

good choice tigerdunes.

here is your answer OP.

Thanks again for the help and precious hints!

I just checked the 802 vs 803. The 803 has a humidity sensor.
With the 802 will the AC dehumidify as long and as much as it runs or not at all? All dealers told me the big advantage of the new 2 stage units is the dehumidifying capability coupled with the fact that they run longer in low power.
What's the difference between the 2 coils (4TXCD063BC3 and 4TXCC008CC3HCB )?

What about the filter? One dealer told me that the real filter in the box is a Honeywell anyway, so the same for Trane as for Lennox (the 25x20x5' in my case). If true, is the Merv 10 with a CADR of 520 a problem/ huge bottleneck?

Wouldn't the Lennox with a SEER of up to 21 be a "better" choice for the 8.5K or why not?

Angel

I will say upfront that I think Trane is a step above over Lennox.

You fail to identify the size of Lennox furnace quoted. I assume it is the 90 K model. These model numbers of condensers never have the full SEER ratings especially in larger sizes.

Here is the matching AHRI number. You should confirm with your dealer.

5991283 Active Systems XC21 SERIES LENNOX INDUSTRIES, INC. XC21-048-230-10 CH33-50/60C+TDR+TXV 1595 1100 SL280UH090XV60C* 49500 13.00 17.70 1 RCU-A-CB 338 Yes

I personally think you are fretting too much over the filter box. Yes, Honeywell makes many of the cabinets and filters for many brands. I like Trane Perfect Fit because it is physically made to fit their furnaces. I have that model. Changeout is easy. OEM or generic replacement filters are readily available and with various MERV ratings.

Yes, the 803 thermostat has a humidity sensor for improved dehumidification. Otherwise the 802 and 803 are identical. And just so you know, the 8320 and 8321 are the identical Honeywell model numbers to Trane's 802 and 803 and will be less expensive.

I think either system correctly sized will do you a nice job. I just like Trane over Lennox. The price difference really is inconsequential. I probably would take into consideration which dealer you have the most confidence in. I am not against reusing existing lineset. However, the lineset must be the correct size to new condenser. If not you shortchange yourself on system's capability and performance/efficiency numbers.

Rely on dealer for best coil selection for your application. But verify performance/ efficiency numbers in AHRI Directory. Unfortunately many dealers look out for themselves in this area rather than their customer.

IMO

This post was edited by tigerdunes on Thu, Oct 24, 13 at 7:19

"Wouldn't the Lennox with a SEER of up to 21 be a "better" choice for the 8.5K or why not?"

The key words in your sentence are "up to 21". This is sales puffery. What this means is there is at least one Lennox condenser and furnace combination which when tested in a lab under ideal installation conditions reaches will reach a SEER rating of 21. Your configuration will be less.

Do you believe the EPA mileage ratings for a car? Ever hear the term "your mileage will vary"?

Don't choose an AC solely on reported SEER ratings.

If I understood my dad correctly (self-employed and incorporated in HVAC industry for 38 years), in my area, it is now against some law to install a central system that is larger than what is needed according to the load calculation. I believe when the contractor pulls the permit, the system needs to coincide with what the LC is, and they won't approve the work at the jobsite until an LC is done (forcing another charge for the homeowner to pay). I'm in Mobile County, Alabama. A load calculation will tell your installer what he should put in.

If you had a 4-ton, I'd go back with a 4-ton; unless your unit ran all the time in the summer, then I'd go with a 4.5 ton. Although there are other factors to consider, as explained in all the wonderful responses you've received in this thread.