How your system works6 min readSeptember 12, 2026
Why North Texas HVAC systems age faster: the attic, the ducts and the clay
Most homes here sit on slabs, so the air handler and the ducts live in the attic, which reaches 130 to 150 degrees on a summer afternoon. Every duct leak dumps cooled air into that heat, the equipment runs more hours than the national average, and the shifting clay under the house pulls duct joints apart over time. The practical answers are a duct leakage test, sealed and insulated ducts, and an attic that is vented or insulated well enough to take the edge off.
Why the equipment is up there
Basements are rare on expansive clay, so builders put the furnace or air handler in the attic and ran flexible ducts across the ceiling joists. It is cheap to build and expensive to live with: the system that cools the house sits in the hottest space on the property, and every foot of duct is surrounded by air far hotter than the outdoors.
What the attic does to the ducts
Flexible duct is a wire coil wrapped in plastic and a thin layer of insulation. Over years at 140 degrees the plastic inner liner becomes brittle, the insulation compresses, and the tape at the joints lets go. Typical duct leakage in homes under ten years old in Frisco and McKinney runs 20 to 30 percent when tested, which means a quarter of the cold air you paid for is cooling the attic. Supply air that starts at 55 degrees can arrive at a far bedroom at 65.
What the clay does
The Blackland Prairie clay swells when wet and shrinks when dry, and the foundation moves with it in small amounts each year. Framing shifts, the furnace platform tilts, the plenum pulls away from the furnace, and rigid duct connections crack at the seams. It is why a duct system that tested fine when the house was built can be leaking badly at year eight with no single event to blame.
What this means for repairs
Systems here run more hours per year than almost anywhere in the country, so a 12-year-old system in Plano has the wear of a 16-year-old one in Ohio. Capacitors, contactors and fan motors fail younger. The useful response is maintenance that measures static pressure and temperature split, because those two numbers show duct and airflow problems before they turn into equipment failures. A duct test before any replacement is not optional; a new system on leaking ducts is money wasted.
What helps
- A duct leakage test, with sealing at the boots, the plenum and the joints, which often returns more comfort than a bigger unit
- R-8 insulated flex duct on replacement, not R-6, and runs that are pulled straight rather than snaked
- Attic insulation brought to current code depth and a working ridge or power vent
- A radiant barrier on the roof deck, which drops attic temperatures noticeably in our sun
- Returns sized to the system; most builder homes have too little return air, which is the hidden cause of a lot of noise and a lot of frozen coils
Questions on this
Is it worth moving the system out of the attic?
Rarely practical on a slab home. Sealing and insulating the ducts, and reducing attic temperature, gets most of the benefit at a fraction of the cost.
How do I know if my ducts are leaking?
Rooms that will not cool, a system that runs constantly in the afternoon, dust that reappears quickly, and a filter that loads fast are the signs. A duct leakage test with a calibrated fan gives a number.