Why it matters to you
In humid Greater Houston, a system that is too big cools the air fast and shuts off before it removes much moisture, leaving the house clammy and the equipment short cycling. Capacity also sets which federal minimum applies: in Texas, split air conditioners below 45,000 BTU/h must reach 14.3 SEER2, while larger ones must reach 13.8 SEER2.
Practical guidance
Ask every bidder how they arrived at the tonnage on their quote; "same as the old unit" or a square-foot rule of thumb is not a load calculation. Your outdoor unit's model number usually encodes its nominal capacity, which a technician can read for you.
How many tons of AC does my house need?
The answer comes from a Manual J load calculation, which accounts for insulation, windows, orientation, air leakage, duct location and local design temperatures. Square-footage rules of thumb ignore those factors and often lead to oversizing. Two Houston homes of the same size can need different tonnage.
Why is an oversized AC a problem in Houston?
An oversized system reaches the thermostat setting quickly and shuts off before the indoor coil has removed much humidity, then starts again minutes later. That short cycling leaves the house cool but clammy, wastes energy on frequent starts and adds wear. In a humid climate, a bigger system is not a better one.
Should I replace my AC with the same tonnage as the old one?
Not automatically. Copying the old unit's size repeats any original sizing mistake, and insulation, window or duct changes since the house was built may have changed the load. A new load calculation confirms whether the same tonnage, or a different one, fits the house today.
Does tonnage change the SEER2 minimum?
Yes, at the 45,000 BTU/h line, which is just under 4 tons. In the DOE Southeast region, which includes Texas, split air conditioners below 45,000 BTU/h must be at least 14.3 SEER2 and those at or above it must be at least 13.8 SEER2. The rating that counts is the system's certified capacity, not its nickname.