When AC alone is not enough
Air conditioning removes humidity as a side effect of cooling. That works most of the time in Houston - but two scenarios break it. First, mild but humid days (60-75 deg F outdoor with 70+ percent RH) - the AC barely needs to run for cooling, so it does not run long enough to dehumidify. Second, well-sealed newer homes where internal moisture sources (cooking, showering, breathing) generate humidity faster than the AC's run time can remove.
If you have a smart thermostat that reports indoor humidity and you watch it through a Houston spring or fall, you will often see indoor RH climb to 60-65 percent on shoulder-season days. That is the dehumidifier-needed scenario in plain numbers.
How a whole-house dehumidifier works
Ducted whole-house dehumidifiers (Aprilaire, Honeywell, Santa Fe, Ultra-Aire are common brands) are essentially refrigerant-based dehumidification engines built into a small cabinet (about the size of a large suitcase). They install in the duct system, typically pulling air from the return trunk, dehumidifying it, and returning it to the supply trunk OR ducting it directly into a central living area.
A built-in humidistat senses indoor RH and runs the unit only when needed. The condensate drains to a floor drain or condensate pump - the same way your AC's condensate is handled. Once installed, you set your target indoor RH (usually 50 percent) and forget about it.
Sizing - pints per day
Whole-house dehumidifiers are rated by pints of water removed per 24 hours at AHAM standard test conditions (80 deg F, 60 percent RH). For Houston homes:
- 70 pints/day units fit most homes 1,200-2,000 sq ft.
- 90 pints/day units fit most homes 2,000-3,500 sq ft.
- 120+ pints/day units fit larger homes, multi-zone systems, and homes with strong internal moisture loads (gyms, indoor pools).
Undersizing a dehumidifier is the most common installation mistake. A 70-pint unit running constantly in a 2,800 sq ft Houston home will never reach setpoint; it will just wear itself out.
Installation details that matter
- Discharge to supply duct vs to a central return: both work, with tradeoffs. Supply-duct discharge requires the AC blower to run when the dehumidifier runs (more electrical cost). Direct discharge to a central return can short-circuit if not designed carefully.
- Drain line slope and trap: condensate drain must slope down continuously and have a trap to prevent air leaks back through the drain.
- Electrical: most residential whole-house dehumidifiers run on standard 120V, 5-7 amps. Some larger models need 240V.
- Filter: whole-house dehumidifiers have their own filter (typically MERV 8). It needs replacement annually.
Should you get one?
Yes, if any of these are true: indoor RH consistently above 60 percent in summer despite a healthy AC; indoor RH above 55 percent in spring and fall (shoulder seasons); persistent musty smell, mildew on bathroom ceilings, or mold spots in cabinets; high-occupancy or moisture-generating activities (large family, indoor cooking enthusiasm, indoor plants in volume); or you set the thermostat at 76+ deg F to save on bills and have noticed humidity creeping up.
No, if your AC is oversized or your ducts are leaking - fix those first. We will tell you which scenario you are in before quoting equipment.