The short answer
Only if the air conditioner, correctly sized and working properly, still cannot keep indoor humidity under 60 percent. The EPA suggests below 60 and ideally 30 to 50 percent. On the coast the gap usually shows on mild spring and fall days, when the AC barely runs.
Why does a cool house still feel clammy?
Comfort is not temperature alone. It is temperature and relative humidity together, and in this climate the humidity half does most of the damage. A house at 73 degrees and 65 percent relative humidity feels muggy and smells musty; the same house at 73 and 50 percent feels fine.
Air conditioning dehumidifies as a side effect of cooling: warm, humid air passes over a cold coil, moisture condenses on it and drains away. That only happens while the system is actually running — which is the whole problem on a mild day.
Could the air conditioner be the real problem?
Rule these out first, because none of them needs new equipment:
- An oversized system that cools quickly, shuts off, and never runs long enough to pull water out
- The blower set to run continuously, which re-evaporates water off the wet coil
- Duct leaks pulling hot, humid attic or crawlspace air into the system
- A blocked condensate drain putting water back where it should not be
- Bath and kitchen fans that do not actually vent outside
When does a dedicated dehumidifier make sense?
When the equipment is right and humidity is still high. A whole-home dehumidifier works independently of the cooling call, so it holds humidity in range on the mild days when the air conditioner barely runs at all — which, on the Georgia coast, is a large part of spring and fall.
Tightly built newer houses are the other common case. A well-sealed house holds on to moisture that a leaky one shed by accident, so drying has to be designed in.
How do you know before spending money?
Measure. An inexpensive digital hygrometer, or a thermostat that displays humidity, read at different times of day over a week or two, tells you more than any impression. Readings that sit above 60 percent while the system is healthy are the case for a dehumidifier; readings in the 40s and 50s are not.
Other signs worth noting: condensation on windows or on supply registers, a musty smell that returns after cleaning, and mold on bathroom ceilings or around vents.
What does it cost, and how is it installed?
A whole-home dehumidifier starts at $1,795, and an indoor air quality assessment that measures the problem first starts at $149. The unit is ducted into the existing system, drains to the condensate line, and runs on its own humidity control.
A portable dehumidifier is fine for a single room, but it has to be emptied, it adds heat and noise to the room, and it cannot dry a whole house.
Also asked.
- What humidity should my house be in summer?
- The EPA suggests keeping indoor relative humidity below 60 percent, and ideally between 30 and 50 percent. Above 60, mold and dust mites thrive and the house feels muggy even when it is cool.
- Will a dehumidifier raise my power bill?
- It uses electricity of its own. The offset is that drier air feels cooler, so many households are comfortable with the thermostat a degree or two higher once humidity is under control.
Sources
- ↗A Brief Guide to Mold, Moisture and Your Home — U.S. Environmental Protection Agency