I am replacing two 5 ton units in a dual system home with lots of open space and 20 foot ceilings in 1/3 of it. While efficiency is important the most important thing is a unit that can be relied on to need the least maintenance and repairs. Basically, which is better, provides the cleanest air and has the best features. Both units have been recommended by different installers, the Carrier 21 or the Lennox xc 21.

Carrier is a good product but it is actually the install that makes the difference.