Dang..How can you possibly live in San Antonio and NOT use the AC?
I live in Bastrop (Austin area) and can't imagine not using the AC in
the
hot humid summers.
Heating is what I would expect not to use much here..

I know, everyone tells us one can not survive w/o a/c, but we managed
just fine since 2002 in a house w/o a/c. Fortunately both of us prefer
it like that - the one thing I really hate about Texas in the summer is
that you have to carry a bloody jacket or fleece with you everywhere
you go thanks to the a/c. I've lived in much hotter climes in the
tropics, so it's normal for me (and I grew up in east LA w/o a/c - not
as humid, but much hotter). Oddly enough, DH is from Switzerland but
also prefers the lack of a/c.

That the house was built pre-central a/c days, it is well situated with
high ceilings, pier/beam foundation, lots of shade trees, windows in
appropriate places, etc.

We're installing it due to aforementioned people who swear one can not
survive w/o it. Since those will likely be the potential buyers in 5+
years time.