The Bigger-Is-Better Myth
Many DFW homeowners assume they need the biggest AC possible to handle Texas heat. This is one of the costliest mistakes in home comfort.
An oversized AC creates multiple problems:
- Short cycling — Turns on and off every 5-8 minutes instead of running 15-20 minute cycles
- Poor dehumidification — Doesn't run long enough to remove moisture, leaving your home cool but clammy
- Uneven temperatures — Blasts cold air briefly then shuts off, creating hot/cold swings
- Wasted energy — Startup draws the most power; frequent cycling wastes electricity
- Premature wear — Components endure more start/stop stress, shortening system life
How to Properly Size an AC System
The industry standard is a Manual J load calculation — a comprehensive analysis that considers:
- Square footage and ceiling height
- Number and type of windows (single-pane, double-pane, Low-E)
- Window orientation (south/west exposure = more solar heat)
- Insulation levels in walls, attic, and crawlspace
- Number of occupants
- Kitchen and appliance heat loads
- Ductwork design and location
- Building tightness (air infiltration)
A rough estimate is 400-600 sq ft per ton in the DFW area, but this varies dramatically based on the factors above. A well-insulated newer home might need 500-600 sq ft per ton, while an older home with single-pane windows might need 350-400 sq ft per ton.
DFW-Specific Sizing Factors
Attic temperature: DFW attics regularly exceed 140°F in summer. If your ductwork runs through the attic (as most DFW homes do), duct heat gain can add 0.5-1 ton of required capacity.
West-facing windows: Large west-facing windows can add significant heat gain during afternoon hours. This is especially impactful in newer suburban DFW developments with large windows.
Design temperature: AC systems in DFW are sized for a 100-103°F outdoor design temperature. The system should maintain 75°F indoors when it's 100°F outside. During the handful of 108°F+ extreme days, even a properly sized system may struggle — this is normal.
Humidity load: DFW's humidity adds to the cooling load. This is factored into the Manual J calculation but is another reason why oversizing is problematic — the system needs adequate run time to dehumidify.
Consequences of Wrong Sizing
Oversized (too much capacity):
- Short cycling and poor dehumidification
- Higher energy bills (10-15% more than right-sized)
- Reduced comfort despite adequate cooling capacity
- Shorter equipment life due to cycling stress
Undersized (not enough capacity):
- System runs continuously on extreme heat days
- Can't maintain desired temperature during peak afternoon hours
- Higher energy bills from constant operation
- Accelerated wear from non-stop running
Right-sized:
- Runs 15-20 minute cycles for optimal dehumidification
- Maintains temperature efficiently
- Long equipment life
- Comfortable, consistent temperatures throughout the home
Spencer performs Manual J calculations on every installation. We'll never recommend a system that's too big or too small for your home.
Call 972-446-2665 for a free in-home sizing consultation.
Spencer Air Conditioning & Heating — Right-Sized Comfort Since 1960.