William, I am sorry, I can't be of any help, but I will be watching this thread for any answers. My hubby and I are replacing two AC units and are currently trying to find info/comparisons/real life cost savings for the Trane products. We are also looking for info on the variable speed units vs a single stage unit. The one difference between you and us is that we will be going from 2-10 seer units to a 14 and 16, possibly 18 seer. So I am sure we will see savings. Both of our units are 14+ years old and limping through the summer with HUGE electric bills. Enough is enough and we are replacing.

What size is existing furnace? There is a great deal of hype from the major brands who do most of the heavy advertising about savings. Most of it is nonsense and you will never ever see the savings that they promise. Now, you must have a var speed or high eff blower on your furnace when paired with high eff condensers whether single stage, 2 stage, or variable. I always like to see to see that a new system is a matching system and you can get both performance/efficiency numbers on the condenser from the AHRI Directory. Obviously you will see heating savings on nat gas going from 80% eff to 90+% eff from your condensing furnaces whether single stage, 2 stage, or full modulating. On AC, rule of thumb says you will save around 5% for each point increase in SEER. Don't bank on it.

i will say up front I am not a fan of Lennox brand. My bias. For your location/climate, I would suggest at the minimum Trane 2 stage XV95 furnace-most likely 80 K size paired with 4 ton 2 stage XR17 or XL18i AC condenser. Exact same available from sister company American Standard. Carrier/Bryant would offer similar models and good quality as well.. Beyond that you will be paying more for additional comfort with modulating furnaces and variable speed condensers. I think that is overkill and not necessary for your location/climate. But why not if you plan to be there a long time and have deep pockets.

IMO

In 2009 I replaced two single stage furnaces and AC condensers, with a variable speed furnaces and 2-stage condensers. The equipment was 25 years old when it was replaced. The furnace efficiency went from the advertised 78% to 95%, the condensers went from 8 SEER to 14.5 and 15.5.

I have been calculating the heating and cooling costs for the past three years for my 3200 sq. foot house. I had some numbers before the upgrade. The heating savings has been significant, but a lot of that is due to the price of gas going down. I would have to pull out all the old utility bills to calculate the savings by therms. I have gotten some savings with the AC, but as my daughters get older they want the house to be cooler, so I have lost control of the thermostat. I agree with Tigerdunes the savings on a new AC is no where near to what the SEER ratings suggest. The 2-stage condenser can provide some small savings if you can lower the humidity and set the thermostat 1 -2 degrees higher.

Have you calculated how much money you spend on heating and cooling each year? You need those numbers in order to calculate the return on investment. I have come up with method that generates approximate costs.

Can you post the quotes showing a $5K difference in prices? That seems like a big difference in prices between the low and high end. Carrier and Trane have some very high end equipment that is very expensive and difficult to justify in most parts of the country. There may be models that are more efficient and provide comfortable that have a more reasonable price.

Put in a new A-coil, and you're good. You will never save any money on a new system, as the higher seer units have nothing but problems. Do a search.

I don't understand the above comment. While you have a point of view about repairs and patchwork, sometimes bandaids just postpone the inevitable and possibly not be cost effective depending on age and efficiency of equipment. Anything mechanical will eventually break and have to be replaced. Certainly though I would never say HVAC is an investment nor will high end HVAC have a reasonable payback. Not the way to look at HVAC. Depending on location/climate it is more closely aligned with being a necessity.

IMO

I don't sell hvac equipment do you?

first of all, let me say that a variable speed blower does not require a 2-stage or variable speed condenser. You can still use a variable speed blower with a single stage condenser. And having lived with both I can say I will never have a single speed blower again. My house is much more comfortable with the variable speed blower that it was before. I cannot speak realistically about savings since I went from 8 SEER to 14 SEER, but I did notice a difference.

Going from 13 to 14 for you might save $5 a month but I doubt you'ld ever see it. Going from 80% to 95% on the furnace would be more significant but I wouldn't pay $5000 for it. Maybe getting a quote for a 2-stage %90 furnace would be a good idea

To get a 16 seer 4 ton from an hvac dealer, you're going to spend $8000. That will pay quite a few monthly electric bills with an old system.

Thanks to all the comments. Based on feedback from this thread as well as additional research, we've decided to go with one of the non-variable speed options. After receiving and thoroughly reviewing all the quotes, we could have moved up to VS for an additional $3k (not the $5k I stated in the original post). Still, we could not have made up the difference in utility savings vs the 16 Seer / 2-stage 95 furnace option. Since comfort and noise had never been issue with our old 14 Seer system, there was really no other reason to consider the VS option. We will be going with a 16 Seer single stage AC with a 95 AFUE 2-stage furnace (or thereabouts depending on the vendor selected). We are still in negotiations between Trane, Carrier, and Lennox, so haven't determined equipment / installer yet. For those interested, I will be keeping tabs on my utility bills and posting my results. This will be versus a 15 year old Trane XL1400 (3.5 tons) and 15 year old Trane XE90 (also 3.5 tons).

What furnace Mdl are you considering? If looking at high eff AC condenser 15+ SEER, you will need at the minimum a high eff blower on a Sgl stage furnace or a var speed blower on a 2 stage furnace. Otherwise you would be just throwing your money away.

IMO

William - have you been keeping track of the utility bills? What have you found?

I've been keeping track, but had not done any analysis until you posed the question. As you can see from my comments, I chose NOT to go with the variable speed AC/Heat unit. Even so, I've seen a notable reduction in my utility bills. And keep in mind that this is only replacing the upstairs AC / Heat. The downstairs in on the verge of failure after 16 years, so I will be doing something similar with it in the near future. Here's my analysis of pre/post installation:
Pre-New System
Post New System
Comp Periods
9/1/2014-5/31/2015
9/1/2015-5/31/2016
Difference
% Change
Avg Temp (Fahr)
55.1
57.7
(2.6)

Average Bill $'s$252.18
$208.06
$44.12-17%
Avg Cost/Day $'s
$8.33$6.83$1.50

-18%

I'm down about 18% on a per day basis. By my reckoning, about 4-5% of that is due to lower natural gas rates, and another 4-5% is due to the difference in temperature over the winter. So net-net, down about 8-10% on tried and true technology. I would expect to get something similar when I replace the downstairs unit.

salti - what changes did you make to the a/c system?