Ductwork and Airflow in Pattison

Cooling leads the year in Pattison, and the installer sizes the duct around the cooling load — where anybody sized it at all. More often than not that works in your favor: a system with a furnace moves less air in heating than it moves in cooling, and a heat pump moves the same air in both, so a run sized to carry the house through August usually carries it through the few cold weeks either way.

The short winter decides where the loss lands rather than whether there is one. A joint in a vented crawl space or an unconditioned attic leaks at the same rate in every month of the year; here it leaks through a cooling season that runs most of the year and a heating season measured in weeks. So almost everything a duct leak costs here is written in summer, and the time to get a contractor under the house is before that season rather than in the middle of it.

Heating here is short enough that people put up with a cold room — a few weeks of a back bedroom nobody sits in, and then it is spring. That same run is the one that will not cool in July, and by then it has been wrong for a year. Usually it is the room at the end of the longest run, which is the one the air reaches last in either season.

July here is humid enough that duct picks up a failure dry climates never see: a supply run crossing an unconditioned attic or crawl space carries air near 55°F through air whose dew point is above 70°F, and where the insulation is torn, compressed or missing, the duct sweats. Water runs downhill to the low point of the run, and it turns up a floor below, some distance from the joint that made it. A return leaking in the same space does the other half — it draws that outside air in at its own dew point, and the coil spends its capacity drying attic air while the house stays cool and clammy.

The filter is the one thing in the aisle that changes airflow at all, and where it has not been changed since the last season it is worth doing before the phone comes out. What it cannot do is reach any further than itself: a filter gives back the air the system already had, and it does nothing for a run that is crushed, pulled off its collar or leaking into a crawl space, and nothing for a return that was always too small. The version that backfires is the upgrade: a dense one-inch filter sold for allergens takes more pressure than the slot was built for, and a system already short of air gets shorter. If the room is still wrong with a clean filter in, the filter was never the answer.

Duct tape is named after the job it fails at. On a warm duct the cloth-backed roll dries out and lets go, usually inside a couple of years, and the joint is open again with nothing to show for the afternoon. What holds is mastic brushed on, or foil tape carrying a UL 181 marking on the roll — and both want the joint clean and dry, which is the hard part in a crawl space.

Closing the registers in rooms nobody uses is the fix that feels obvious and is not. Air does not redistribute itself, it raises the pressure in the duct, and higher pressure pushes more of it out through every leak the system already has. Easing one register in a room that overshoots is a different thing, and that is what a damper does — the difference is one adjustment against half the house closed off. A booster fan at a register does anything at all only where the run behind it is sound, and on a run that is leaking or pulled off its collar it changes nothing.