Square-foot rules of thumb get AC size wrong more often than they get it right. The right size comes from a load calculation of your actual house.
Why rules of thumb miss
“One ton per so many square feet” ignores insulation, windows, which way the house faces, ceiling height, air leaks and how many people live there. Two homes with the same floor area can need very different systems.
What a Manual J load calculation looks at
- Insulation levels in walls, attic and floors
- Window size, type and direction
- Air leakage and ventilation
- Local design temperatures for Salt Lake County
- Occupants and heat from appliances
Aegis runs a Manual J load calculation on every installation.
What goes wrong when an AC is oversized
- Short cycling: it cools fast, shuts off, and starts again, which wears parts
- Uneven temperatures between rooms and floors
- Higher upfront cost for capacity you don’t use
What goes wrong when it’s undersized
It runs nonstop and still can’t keep up on the hottest afternoons.
Ducts matter too
A correctly sized AC on ducts that are too small or leaky still underperforms. We check the ductwork as part of every install estimate.
Real right-sizing jobs
- 1980s rambler in West Valley City: 3-ton unit right-sized to 2.5 tons
- Two-story home in Taylorsville: 3.5-ton unit right-sized to 2.5 tons
Typical Aegis AC installation is $4,500–$9,500 with a free written estimate. AC installation · pricing.
Frequently asked questions
How do I know what size AC I need?
From a Manual J load calculation of your home, not from square footage alone. Aegis does one on every installation.
Is a bigger AC better?
No. An oversized AC short cycles, wears faster and cools rooms unevenly.
Should my new AC be the same size as the old one?
Not necessarily. Many older systems were oversized. Several Aegis case studies replaced oversized units with smaller, right-sized ones.
Guide: how the Salt Lake Valley climate affects heating and cooling.