Heat pump water heaters do not dehumidify; instead, they extract heat from the air to heat water, which can slightly lower humidity levels in the immediate area, but their primary function is water heating, not dehumidification.
Heat pump water heaters (HPWHs) offer an energy-efficient way to heat water while potentially reducing humidity levels in your home. But how effective are they at dehumidification compared to dedicated dehumidifiers? This article explores the science behind HPWH dehumidification, real-world performance data, and whether they can replace standard dehumidifiers.
How Heat Pump Water Heaters Remove Moisture
HPWHs work like air conditioners in reverse. They extract heat from surrounding air and transfer it to water in the tank. As air passes over the cold evaporator coils, moisture condenses when the air reaches its dew point. This process is identical to how convection heating systems manage air flow, but with opposite thermal effects.
The Dehumidification Process
When warm, humid air contacts the cold evaporator coils:
- Air temperature drops below dew point
- Water vapor condenses on coils
- Condensate drips into drain pan
- Dryer, cooler air returns to room
Dehumidification Performance Data
Studies show HPWHs can remove significant moisture, but results vary by:
| Factor | Impact on Dehumidification |
|---|---|
| Baseline humidity | Higher RH = more condensation |
| Hot water usage | More usage = longer run time = more dehumidification |
| Climate | Humid climates see greater benefits |
Real-World Measurements
A Kentucky homeowner recorded these annual averages from two HPWHs:
- 1.5 pints of water removed per day
- Peak removal of 4 pints/day in summer
- Basement RH maintained at 50-60%
HPWH vs. Dedicated Dehumidifier
While HPWHs provide free dehumidification as a byproduct of their operation, they have limitations compared to purpose-built dehumidifiers:
Advantages of HPWHs
- No additional energy cost for dehumidification
- Provides hot water as primary function
- Cools basement spaces in summer
Limitations
- Only operates when heating water
- Cooler exhaust air may be undesirable in winter
- Lower moisture removal rate than dedicated units
For homes with moderate humidity issues, an HPWH may provide sufficient dehumidification. The heat pump water heater vs tankless comparison shows additional benefits beyond just humidity control.
Optimizing HPWH for Dehumidification
To maximize moisture removal:
- Set unit to “Heat Pump Only” mode to prevent electric resistance heating
- Install in basement or other humid space
- Ensure proper condensate drainage
- Size tank appropriately for household needs
Climate Considerations
In humid climates like the Southeast, HPWHs can remove 3-5 gallons of water per week according to U.S. Department of Energy data. In drier climates, dehumidification may be minimal.
When to Use a Dedicated Dehumidifier
Consider adding a dehumidifier if:
- Your HPWH can’t maintain RH below 60%
- You experience condensation on windows
- Musty odors or mold appear
- Your home has basement moisture issues
For severe humidity problems, the ASHRAE Handbook recommends maintaining 30-50% RH for optimal comfort and health.
Maintenance for Optimal Performance
To keep your HPWH dehumidifying effectively:
- Clean air filters monthly
- Inspect condensate drain line quarterly
- Check evaporator coils annually
- Monitor basement humidity with hygrometer
Proper maintenance ensures both efficient water heating and consistent dehumidification performance from your HPWH system.
