Why this is a Houston-specific problem
In a colder climate, ducts run through conditioned basements - a duct leak in a basement just means slightly warmer cooled air. In Houston, almost every home's ducts run through the attic, which routinely hits 130-150 deg F in summer. A 10 percent duct leak there does not just lose 10 percent of your cooling - it ALSO sucks in superheated attic air through return-side leaks and tries to cool that. Energy Star estimates that typical Houston duct systems lose 20-30 percent of their delivered capacity to leaks alone.
Add to that: most Houston homes were designed by builders working from rules of thumb, not engineering calculations. Long supply runs to back bedrooms are routinely undersized. Returns are often a single grille in a hallway that cannot move enough air for the closed-off rooms. The result is the comfort gap most homeowners describe - the kitchen and living room are perfect; the master bedroom is two degrees warm; the kids' bedroom over the garage is five degrees off.
The five common causes
- Leaky ducts. Tape failures, mastic that has cracked, joints that have separated, register boots not sealed to drywall. The fix is duct sealing - mastic, foil tape rated UL 181, or a system-wide aerosol sealant like Aeroseal.
- Undersized supply trunks or branches. The far bedroom has a 6-inch flex duct trying to deliver 200 CFM that needs a 7-inch. The fix is upsizing the supply, often without touching anything else.
- No return air in the room. When a bedroom door closes, the supply still pushes air in but the return cannot pull air out. Pressure builds up, air leaks out windows and doors, the room gets stuffy and warm. The fix is a transfer grille over the door or a jumper duct to the return.
- Wrong register positioning or size. A supply blowing directly at a return short-circuits before it cools the room. A supply hidden behind furniture starves the space. The fix is moving or replacing the register.
- Crushed or kinked flex duct. Flex ducts step on or stuff into impossibly tight spaces drop airflow dramatically. The fix is rerouting and supporting the duct properly.
What a real airflow diagnosis looks like
When we diagnose an uneven-comfort complaint, we measure - we do not guess. The four measurements that find the answer:
- Static pressure across the air handler (target: under 0.5 in. wc; high static = restricted airflow somewhere).
- CFM at every supply register, using an anemometer and the register's measured free area.
- Return-air CFM, again with an anemometer at the return grille.
- Temperature drop room by room (Delta-T from supply register to return).
From that data, the math is unambiguous. We can tell you whether the system is delivering its rated airflow, where it is being lost, and which fix has the highest impact. We will not sell you zoning hardware to mask an airflow problem that costs $400 to fix at the duct level.
What you can check yourself
- Walk the attic with a flashlight (carefully). Look for crushed flex ducts, separated joints, or duct sections collapsed by foot traffic from past trades.
- Check supply register positions. Are they pointing at occupants or at the back of a couch? Are they obstructed by furniture, drapes, or rugs?
- Listen at the return. A whistling, moaning return is undersized - the system is starving for air.
- Check whether closing a bedroom door changes its temperature. If yes, you need a return path.
- Check for tape on duct joints. Cloth duct tape (the gray fabric stuff) was never rated for HVAC. UL-listed foil tape and mastic are the only correct sealants - if you see anything else, it is failing.