"Ook" Ook Don't send me any freakin' spam at zootal dot com delete the
Don't send me any freakin' spam wrote

Because I've spent too many years living in houses with a/c units that
were sized according to the house size, and most of them ineadequate. When
it hit 110+ outside, we sweltered inside because the a/c just couldn't
handle the load.
I wonder if the problem is that the contractors use the smallest unit they
can get away with, instead of one that will cool the house even when the
weather hits 118? IOW, a competent estimator would indeed give the right
size to use, but those that build houses like to cut costs when they can,
including using small a/c units?

Wonder no more. Builders use as cheap as they can get away with.

The manual J is a very good method of determining the size AC you need, but,
it is dependent on proper input. If you design for a 20 degree differential,
but want a 30 degree differential, it is not going to work.

What works for me so far, is not to live in a place where the temperature
reaches 118 degrees.