Price is around $1500-2000 more than I would expect. That unit isn't even one of the premium units, and will only have a 5 year parts warranty. The system does qualify for the tax credit, and as this would be a selling point, it's not unlikely that the price is a bit inflated for this reason. I'd keep looking. Sounds like a straightforward changeout with the exception of a new copper lineset. Sounds like an attic install, and may be a bit challenging. New outdoor pad is standard practice on any changeout.

Dear ryanhughes -- Thank you! I appreciate your very helpful response. We're going to keep looking. I've two follow up questions, if you have time.

1. He also said something I didn't understand -- that only the XB14 3.5 ton would be efficient enough in our house to qualify for the tax credit, i.e., that the 3.5 ton versions of the higher-end systems with the better warranties would be inefficient even when combined with a variable speed blower. Does that make sense?

2. We'd like to be able to expand our options as we search. Are there other brands that are really good?

To answer your first question, yes, their is a better 3.5 ton unit that still qualifies for the tax credit. The XR15, which is mechanically very similar if not identical to the XB14, will be a bit quieter and have a 10 year warranty on all parts when registered with Trane -- versus 10 years compressor / 5 years all other parts with the XB14). So it is worth looking into. Model number will be 4TTR5042E1. He may not have bothered quoting it because it is a very similar unit mechanically to the XB14, but the warranty makes it worth it -- unless you were already purchasing a 10 year extended warranty with either system.

2. Finding the right contractor is your primary concern. Brand makes a slight difference in terms of features and efficiency, but overall, most premium units today have 10 year warranties and utilize many of same parts. Not easy today to say that one brand is more reliable than the other.

It looks like we'll go with another installer and another brand. We've decided on Carrier, with a combo that the AHRI website indicates will get us the tax benefits:

Outside: 3.5 Ton Comfort Model 24ACC6 (16 SEER)
Inside: Comfort Series FX4 (13 SEER)

I hope this is a reasonably good combo. The quote still seems a little high at $7660, but I understand they'll have to do some work to get the system into the attic (just a small opening) and that we're buying at probably the worst time of year.

They did say that if we want to save a few dollars we could re-use the lineset that's in place -- they'd flush it. Is it okay to do this or is it best to replace the lineset?

The lineset can be reused if flushed, but it's always a safe be to replace it, and I personally would if possible. You've been quoted good equipment, but you're sacrificing the variable speed indoor blower motor that the Trane setup had. Ask for the price difference to upgrade to the FV4 series indoor fan coil.

I think you are putting that guy's kid through Yale. Get at least ten bids and then narrow it down. I have 2 rental homes and my home here in FL and had replaced all the HVAC units. It was a "teachable moment" learning about HVAC. I enjoyed most of the contractors advice, but a few were a bit greedy. You have to know exactly what you are buying, what they are going to do etc... Are you going to get the duct work cleaned before/during the installation? That is a good idea if it is old and dirty.