I really wish I would've this site before all this started, but here goes:

My wife and I have a seven year old home, 1850 square feet, plus about another 850 square feet of above-ground walkout basement (with crawl space below basement). The original Trane XB1000 2.5 ton outdoor unit which was mated to a 3 ton coil (don't have model number) and a Trane TUE100A948K3 furnace did great in keeping us very cool in the summer. Well, the coil went bad and the XB1000 bit the dust. So we went about getting quotes to replace the system.

Fast-forward. I get quotes and have the system replaced. I tell the dealer I’m going to finish the basement and wanted to know if I need more capacity. He says no, the basement doesn’t count (as he’s standing in it). So the system is replaced with a 2.5 ton XR13 Heat Pump (2TWR3030A1000AA), a 2TXCC037BC3HCAA coil which the dealer says is 2.5 tons, others have told me it’s 3 tons….and TCONT402AN32DA (XR402) thermostat to do “dual fuel”. Well, 90+ degree weather hits and the system can't keep up as well as it used to. At 96 degrees outside, I was only able to maintain 80-81 inside. The other system was able to maintain at least 76 (if not cooler) in this weather last year. Thankfully, this weather doesn’t last too long here in the Midwest.

I had them back out to investigate several times and the tech could find nothing wrong. He sets the thermostat to cycle 6 times per hour instead of the standard 3 and says that'll fix it. It doesn't. The owner then comes out and he measures our rooms and our ducts. As I now know, he should have done this or even more the first time. He tells us for the size of our home, we really need a 4 ton unit! But there’s more bad news. He says our air ducts only support 2.5 tons of airflow and worse yet, our return duct only supports 2 tons of airflow. So, if we want it to be cooler, we need to replace the coil and outdoor unit with 4 ton stuff and also replace our furnace with a variable speed model to increase the airflow. And we also need to replace all the duct work in the basement. He wants to run a trunk line down the I-beam and branch off from that. Currently, there are just individual pipes going to individual ducts out of the plenum. He wants to put dampers in as well to increase the airflow upstairs. He says he feels bad he didn’t spend more time with us the first time and will do everything at cost to him, which was nice. But the cost is way more than I can handle or what I think it is worth putting into this particular home.

So my question is this: Do I really need the ductwork done? Or would bumping the outdoor unit up to 3 tons help? I’m really concerned the 2.5 ton heat pump won’t heat my house this winter since it can’t cool it now. The system is set to switch to gas at 37 degrees, but I still worry. In attempting to do some research online, I see that the TUE100A948K3 may be a 4 ton furnace unit, but I’m still not sure. If this is the case, then why do my ducts only support 2-2.5 tons? Again, we are dealing with about 2800 square feet when you factor in the walk out basement which will be finished soon.

Obviously, I’m a new to this and trying to learn all this stuff. So if you read all this post, thank you so much. Any and all help you can provide is *very* much appreciated.

First off the duct work should have been sized to accommodate the required air flow of the four ton furnace, If the furnace does not get enough air flow across the heat exchanger in the furnace then it will operate at higher then the factory's design temperatures, which means a shorter life expectancy of the heat exchanger.
From this point forward you should reassess your entire system and then do what you can do to achieve a workable and efficient system, even if you just do one part at a time.
Start by calling around your area for a A/C contractor who will do a load calculation on your home and then you will know what parts of your system need the most attention, the entire system has to be matched for air movement, the refrigerant lines are matched for the size heat pump,the size of the heat pump is sized for the cooling load as well, the furnace has to be sized for the heating load.
It appears that the duct work was sized for the heat pump without consideration for the furnace,
If you want to upgrade your system start with the duct work first , good luck, Mike

Your best bet is to have a different company look at your system for a second opinion. At this point I would not trust the company that put the new system in for you until you get verification that the job was done correctly and is operating at maximum efficiency. Something is wrong with this picture when the old unit is the same size as the new and problems come to play.