What Size AC Do I Need? Why Load Calculations Matter
Bigger is not always better. Here is how proper AC sizing works.
Air conditioners are sized in tons of cooling capacity. Choosing the right size is one of the most important parts of an installation, and it is not as simple as matching the old unit or using a square-footage chart.
Why size matters
An oversized system cools quickly but shuts off before removing enough humidity, often leaving the home clammy and causing extra wear from frequent cycling. An undersized system may run nonstop on hot days and still struggle to keep up.
What is a Manual J load calculation?
Manual J is an industry method for calculating how much heating and cooling a specific home needs. It considers:
- Square footage and ceiling height
- Insulation levels
- Window size, type and orientation
- Air leakage
- Local climate
- Number of occupants and internal heat sources
Ductwork matters too
Even a correctly sized system will underperform if the ducts are leaky or undersized. A good installation looks at the whole system.
The takeaway
When you get an estimate, ask how the system size was determined. A thoughtful answer is a good sign.