Dehumidifier Capacity Calculator
Estimate the dehumidifier capacity (pints per day) needed for your space based on room size, current humidity, and environmental conditions.
Formula
1. Volume: V = Area (sq ft) × Ceiling Height (ft)
2. Base Capacity (pints/day):
Base = [10 + ConditionFactor] × (Area ÷ 500)
ConditionFactor: Moderately damp = 0, Very damp = 4, Wet = 8, Extremely wet = 12 (per 500 sq ft)
3. Temperature Factor:
Tfactor = 1 + (T°F − 70) × 0.005
(Each 10°F above 70°F increases load ~5%)
4. Humidity Factor:
RHfactor = 1 + (RH% − 60) × 0.01
(Each 10% above 60% RH increases load ~10%)
5. Additional Loads:
Windows/Doors: 0.5 pints/day each
Occupants: 0.5 pints/day each
Laundry: 4.0 pints/day
6. Total Capacity:
Total = (Base × Tfactor × RHfactor) + Window Load + Occupant Load + Laundry Load
Minimum: 10 pints/day
7. Unit Conversion: 1 pint = 0.4732 liters
Assumptions & References
- Based on the AHAM (Association of Home Appliance Manufacturers) dehumidifier sizing guidelines and the Energy Star dehumidifier capacity chart.
- Baseline assumes a moderately damp 500 sq ft room requires approximately 10 pints/day of dehumidification.
- Temperature correction is derived from psychrometric principles: warmer air holds more water vapor, increasing the moisture load on the dehumidifier.
- Humidity correction assumes a linear increase in moisture removal demand above 60% RH.
- Occupant moisture generation (~0.5 pints/day per person) is based on average respiration and perspiration rates at rest/light activity.
- Window/door infiltration load (~0.5 pints/day each) accounts for outdoor humid air entering the space.
- Laundry load (~4 pints/day) accounts for evaporation from drying clothes indoors.
- ASHRAE Standard 55 recommends maintaining indoor relative humidity between 30% and 50% for occupant comfort and to prevent mold growth.
- Results are estimates. Actual requirements may vary based on insulation quality, climate zone, HVAC system, and specific building characteristics.
- For basements or crawl spaces, consider adding 10–20% to the calculated capacity due to ground moisture infiltration.
- Dehumidifier efficiency decreases at lower temperatures; units rated below 65°F may require a cold-climate model.