By Robert Patterson
The short answer: the right AC size comes from a Manual J load calculation, not a rule of thumb. An oversized system short-cycles, dehumidifies poorly, and wears out early — a real problem in our humid climate where moisture removal is half the job.
What is Manual J?
Manual J is the industry-standard method for calculating a home's actual heating and cooling load — square footage, insulation, windows, orientation, and local climate all factor in. The output is the correct system capacity in tons.
Why oversizing backfires
A too-big system satisfies the thermostat in short bursts, so it never runs long enough to pull humidity out. You get a house that's cold and clammy, higher bills from constant on/off cycling, and premature short-cycling wear. Bigger literally feels worse here.
Why undersizing fails too
Too small and it runs constantly on design days and never catches up — the far rooms suffer first (see why your upstairs is hot). The point isn't small or big; it's right, and that pairs with good duct design.
Your next step
We size every install by load calculation and verify airflow — it's why our systems hit their rated efficiency. Explore AC replacement, read new construction vs. retrofit, and request a quote.