AC size estimator
How big an air conditioner does your Pasadena home need?
Air conditioners are sold by tons of cooling capacity, and picking the wrong size causes real problems. Too small and the system runs all afternoon in a heat wave without catching up. Too big and it cools the air fast, shuts off, starts again, and leaves the house clammy with uneven rooms and extra wear on the compressor.
Try it
Estimate a starting AC size
This estimator gives you a rough starting size for a Pasadena home based on four things you can answer quickly. Use it to understand the range you are in before you talk to a technician, not as the final word. The correct size comes from a full load calculation done at your home.
Adjust the inputs to see a range.
A room-by-room load calculation at your home decides the final size.
How the estimate works
- Enter your conditioned square footage, leaving out the garage and any unheated rooms.
- Choose how well the attic and walls are insulated: poor, average or good.
- Pick how much afternoon sun the house gets through west and south windows.
- Set the typical ceiling height; tall ceilings mean more air to cool.
Related: AC installation, AC replacement, heat pump installation and ductless mini-splits.
Why a load calculation decides the real size
The estimator uses broad rules of thumb. A proper sizing uses a Manual J load calculation, which looks at each room: window size and direction, wall and attic insulation, air leakage, shading from trees, how many people live there, and the local design temperature. In Pasadena that design temperature is far hotter than at the coast, and two houses with the same square footage can need very different equipment. We run that calculation before recommending a system, so the size fits your house rather than a chart.
Size is also limited by the ducts. An old attic duct system built for a small furnace may not move enough air for a larger AC, and forcing more capacity through undersized ducts leads to noise, frozen coils and poor cooling. Older Craftsman and Spanish Revival homes often have little insulation and tight attics, so sealing ducts or adding insulation can shrink the AC you need. The technician checks both before quoting.
Questions
AC sizing questions
Many homes of that size in Pasadena land somewhere around 2.5 to 3.5 tons, but that range is wide for a reason. Insulation, west-facing glass, ceiling height and duct condition all move the number. A well insulated ranch with shade may need less, while an older home with a hot attic and big windows may need more. A load calculation settles it.
Not usually. An oversized AC cools the air quickly and shuts off before it removes much moisture or reaches every room, then starts again a few minutes later. That short cycling wears out the compressor and leaves hot spots. A correctly sized system runs longer, steadier cycles and handles a 100 degree afternoon better than an oversized one.
Sometimes not. Ducts installed decades ago for a small furnace often cannot carry the airflow a larger AC needs. The technician measures duct sizes and static pressure before recommending equipment. If the ducts are the limit, the options are resizing or replacing key runs, adding a ductless head for a hard room, or choosing a variable speed system that works within the ducts.
Need heat or cooling back today?
Call our Pasadena line any hour. A person answers, asks a few questions about the system, and gives you an arrival window.