Most HVAC writing online is either a sales pitch or a repeat of a number nobody can trace. These posts cite the study, name the authors, and link the document. Where good data doesn't exist, we say so instead of inventing it.
Everyone worries about low refrigerant. The field measurements find almost as many systems with too much — usually because somebody topped one off by pressure instead of weighing it in.
Read itEleven field studies, more than 2,600 systems measured in real homes. Only about a quarter held the charge the manufacturer specified. NREL has calculated the national energy cost of that, together with airflow faults, at 20.7 billion kilowatt-hours a year.
Read itThe Department of Energy reviewed decades of field testing on installed residential HVAC. The finding is not that some systems are broken. It is that almost all of them are degraded, and almost nobody knows it.
Read itNIST put numbers on what a refrigerant charge fault actually does. The more useful finding is the one about how differently identical faults behave on different equipment.
Read itA smart thermostat measures the room. The room is downstream of the ducts, which are downstream of the coil, which is downstream of the refrigerant circuit. By the time the room is wrong, everything upstream has been wrong for a while.
Read itCooling is the single largest electrical end use in American homes. That size is exactly what makes a degraded system so hard to spot on a utility bill.
Read itASHRAE publishes a median service life for residential air conditioning. A median is not a promise — it is the middle of a distribution, and half of all equipment lands on the wrong side of it.
Read itIt is not coincidence and it is not bad luck. It is margin. A degraded system keeps up fine until the day the load exceeds what is left of its capacity — and that day is the same day for everyone.
Read itThe CDC has counted heat-related deaths in the United States for two decades. The pattern in that data says something specific about mechanical failures in occupied homes.
Read it