[Atheros]

You're better off guesstimating yourself than trusting contractors. The contractors are incentivized to severely oversize any AC units they install or else people leave bad reviews on their pages/listings when the installed unit can't keep up the one day every two years that the temperature gets abnormally hot.

I did this myself and insisted on a unit half the capacity that the contractors wanted. Several flat-out refused. But it works perfectly! Approximately one day ever two years it can't keep up. Which means that all the other time it doesn't short-cycle. Perfect.

[nocoiner]

I had to replace my home HVAC system this year and went with a variable speed system. It was eye-wateringly expensive, but it works much much much better than the system that was in here before, and completely obviated my concerns about sizing (the old system was an oversized single-stage unit, and the house always stayed cooled, but something or other was regularly breaking, probably due to the short-cycling).

With the new system, electricity consumption on a hot summer day is about a third of the prior system, it’s virtually silent and the comfort of the house (due to more granular temperature control and near-constant dehumidification) is substantially better.