Our home is in the desert, where we cool about 9 months of
the year. When we bought the place, it had two A/C split
systems- a 5 ton and a 3 ton. There were no labels, but a
friend who is familiar with the subdivision and builder told
me that they were built-up no-name units with a SEER or <10
and no TXV. Our electric bill last year for this time of
year was >$500 and the temps were about like this year.
With that in mind, I had a good, reputable A/C company bid
on installing SEER 13 units with TXV's. The price was just
over $9k, installed.
Our home is an "open" design with a second story opening out
to a loft area. It is impossible to keep the cool air
upstairs from flowing over the railing to the downstairs.
Strangely (to me) the 3 ton unit serviced the upstairs and
the 5 ton the downstairs, which is just 25% larger in area.
The A/C company did calculations and measurements, and
told me that a 2-1/2 ton would be just fine for upstairs and
that we did need a 5-ton for the lower level, so I agreed.
The installation was done about two months ago and I was
pleased with the quality of the workmanship I saw. They
even returned on a very hot day to check the Freon levels.
Now for the strange part: The downstairs unit seldom runs
at all. This is what I would expect with the cooled
upstairs air flowing down over the railing. Both intakes
are upstairs- the one for the downstairs is in the ceiling
right over the railing, and the upstairs one is in the
middle of an interior hallway. Our electric bill for the
first really hot month was $250, which naturally includes
all lighting and about 10 hours a day on our pool's pump.
That places it at about $250 less than last year.
The upstairs 2-1/2 ton unit runs about 75% of the time on a
110f day and the upstairs is more comfortable than it was
last year. The downstairs is equally comfortable, which is
a change from last year as well. I am extremely happy with
the results of the switch, but now wonder if there was a
miscalculation on needing the 5-ton unit for the downstairs.
Without knowing the math, from what I've seen so far, a
far smaller unit would probably work just as well, if not
better, because the 5-ton unit goes sometimes 1-2 days
without even running. . . and then runs for under 10 minutes
before switching off.