EngineerHub.orgDescribe the laundry load
Use a preset if you do not know the retained water.
Describe the room
If possible, use a small hygrometer and measure the coldest nearby surface.
How will moisture leave the room?
A fan speeds drying, but ventilation or a dehumidifier must remove the water.
Humidity and drying progress
Worked example: family load in a modestly ventilated room
- The wet clothes contain an estimated 2.5 L of water.
- The room is 35 m³, 20°C and starts at 50% RH.
- The model adds evaporated laundry water to the room air, exchanges moisture with outdoor air and subtracts dehumidifier collection.
- If room RH approaches saturation, evaporation slows toward zero rather than continuing unrealistically.
- The result identifies whether the fastest improvement is better airflow around the clothes, drier outdoor-air ventilation, or a dehumidifier.
Background and recommendations
The model is intentionally practical, but the assumptions are visible.
Cold air may have high relative humidity but low absolute moisture content. When brought indoors and warmed, it can remove moisture effectively. The model compares humidity ratio, not RH alone.
Ventilation exchange is signed: humid outdoor air can add moisture, while drier outdoor air removes it.
US EPA guidance recommends keeping indoor RH below 60%, ideally about 30–50% where practical. A colder window or wall may require a lower winter RH to avoid condensation.
Room temperature is held constant. Textile type, spin speed, actual air velocity, wet fabric surface area and heat consumed by evaporation are simplified. Treat the result as a comparison of setups, not an exact finishing time.
Frequently asked questions
It varies widely with load size, fabric and spin performance. A practical estimate is 1–3 litres for a typical household rack load, but weighing the load wet and fully dry is much better.
Relative humidity depends on temperature. Cold air can contain little actual water vapour; after it enters and warms, it may be able to absorb moisture from the room.
A fan mainly speeds evaporation and reduces damp pockets around clothes. The water still must leave through ventilation or be collected by a dehumidifier.
Fabric, spin speed, rack spacing, heating, air speed and the true moisture content all matter. The model is designed to compare setups, not guarantee an exact finishing time.