The XL15i is Trane's highest efficiency single stage system and a very nice unit overall.

In your case, for a new build, your primary focuses should be proper equipment/ductwork sizing and a quality installation. A properly designed system with good ductwork will help ensure year-round comfort. A 2-stage, variable speed system is an upgrade. The 2-stage system will provide better comfort throughout the home with longer runtimes (hence the need for a properly sized system, single or 2-stage) and therefore more dehumidification. I recommend a variable speed indoor air handler regardless of whether you choose the XL15i, XL16i or XL20i heat pumps (or other). While their summer dehumidification benefits may not be as important to you, one of the main advantages is the blower's ability to maintain a constant cfm (airflow) across varying duct conditions. This means that if the ductwork is less than adequately designed, or if your filter gets dirty and total system pressure drop increases, your airflow won't decrease and the motor will work harder (increase rpm) to meet the required airflow (up to a point, typically 1" external static pressure). This protects the equipment and maximizes performance and efficiency.

I would first get a full load calculation (Manual J) to determine equipment sizing, followed by proper ductwork sizing (Manual J). Once you know where you stand, you can make a better decision on equipment selection. If you cover the right bases in terms of system design and installation, you should be comfortable regardless of which type of outdoor unit you choose to install. The XL16i Trane typically runs around 75% capacity on low stage, whereas the XL20i typically runs around 50% capacity on low stage for a greater split. If you decide on a 2-stage system I would look strongly at the XL20i (the system I chose my for home). The dual compressors are outstanding for part-load conditions, dehumidification, and more even temperatures throughout the home.

Kiely

I am not disagreeing with Ryan's comments. But I do believe one has to weigh what I believe are marginal benefits to the cost of two stage heat pumps.

Here is my general checklist.

There are three equally important aspects of a new installation. Correctly sized and quality HVAC, the install itself by the dealer and his techs, andbfinally and perhaps the most disregarded and overlooked is a decent ductwork system.

both outside and inside units should be replaced to have a properly matched system.

15 SEER, 12.5+ EER, 9 HSPF
best matching VS air handler
full BTUs in both cooling and heating for your rated size
R-410a refrigerant(same as Puron)
scroll compressor preferred
electronic demand defrost preferred
thermostat with "dehumidify on demand" feature
staged backup heat strips
new and correctly sized refrigerant lineset
10 yr warranty on parts and compressor

you want a thorough inspection of your ductwork system. size, overall condition, supply and return lines, insulation qualities, leak test, etc. Since your situation is a new build, I would want several returns both for increased air flow and improved comfort. And I would recommend at a minimum a whole house air filter media cabinet.

My personal recommendation is Trane/AmStd, Rudd/Rheem, and Carrier/Bryant.

Depending on your location, I would not purchase a new system that did not have electronic demand defrost.

IMO

Kiely

While I realize you live in an area with relatively mild summers and winters, you should know that FROGs can be problematic as far as HVAC.

FROGs=finished room over garage

Discuss with both builder and HVAC dealer.

IMO

Thank you all for your responses. I really appreciate it. The reference to (Manual J) was nice because I have been trying to figure out how to determine load calculations on my home. Rheem systems are about 1000 dollars less am I really just paying for the name with Trane?

Kiely

Depending on the model, Rheem is one of the most underrated and overlooked brand in the HVAC residential marketplace. They make nice heat pumps. And just so you know, Ruud is the sister company to Rheem, exactly the same.

IMO

ask what provisions are being made to deal with
f.r.o.g.
these rooms surrounded by extreme attic temps
on 6 sides are very difficult to condition.

best of luck.