We did this in 2005-2006 with both systems that were 15 years old at
the time in north Texas. Similar balance between heating days and
cooling days. We had SEER 10 A/C and 60% AFUE gas heat.
We went with SEER 12 before SEER 13 became the minimum. The smaller
unit was increased from 2.5 to 3 ton on the west side as well as going
to 5" filters from the standard 1". Both are Trane units.
Since then we have replaced every exterior window with triple-pane
vinyl-framed windows this year. We have looked at the radiant barrier
treatment advertisements but have not seriously shopped it.
There are a few items still to consider:
- two-speed fan on the replacement unit
- heat pump vs. conventional
- money put into insulation vs. heating-cooling efficiency: both are a
single-investment, payback-over-time consideration.


On Sat, 27 Sep 2008 23:25:09 -0700, "scorpionleather"
wrote:

I'm ready to replace my 20 year old 10 Seer gas furnace/AC with a full Trane
system. I am confused by all the options (well at least I decided on the
brand), but what I'd really like to know is which units represent the best
balance between short-term cost and efficiency in the long run (especially
the AC part)? Initially I'm thinking, maybe 15 Seer? Living in warm
Southern CA my gas costs in the winter are low but in the summer the AC
electricity costs are very high. Since they don't post the price of the
systems online it is a bit tricky to know ahead of time how to balance this.
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