· Michael Blair
Air conditioning does two jobs: it lowers temperature and it removes moisture. In Middle Tennessee the second job is arguably the more important one, and it is the one that goes wrong most often — usually because the equipment is too large rather than too small.
Why oversized equipment makes it worse
Moisture is removed when humid air spends time against a cold coil. An oversized unit cools the house to the setpoint quickly and shuts off, so the air spends very little time on the coil.
The result is a house that hits 72 and still feels damp, with short frequent cycles. It is the most common comfort complaint in newer Nashville homes with generously sized equipment.
What the number should be
Indoor relative humidity between about 45 and 55 percent is the comfortable band. Above 60 percent a house feels clammy at any temperature and mould pressure rises; below 35 in winter it feels dry and static.
A cheap hygrometer settles the argument. Most people discover their house sits well above 60 percent in summer despite the air conditioning running plenty.
Fixes that work
A variable-speed or two-stage system runs longer at lower output, which is exactly what dehumidification needs. On a replacement it is the single most effective change for comfort in this climate.
A whole-house dehumidifier tied into the return handles it independently of cooling demand, which matters in the shoulder seasons when it is humid but not hot enough for the AC to run.
- Confirm the fan is set to auto, not on — a running fan re-evaporates coil moisture into the house
- Seal crawl space vents and consider encapsulation
- Vent bathroom and kitchen fans outside, not into the attic
- Consider a whole-house dehumidifier for shoulder seasons
The crawl space connection
Much of Nashville’s housing stock sits over a vented crawl space, and in summer that means humid outdoor air meeting cool ground and condensing. That moisture rises into the house.
Sealing and encapsulating a crawl space frequently drops indoor humidity more than any HVAC change, and it addresses the cause rather than the symptom.