The ideal way to dry wet laundry is to hang it outside on a warm, sunny day, but that’s not always possible.
When drying clothes indoors, three main factors determine drying time: temperature, humidity and airflow.
The water molecules trapped in the fabric’s fibres must evaporate by turning into water vapour. This happens as water molecules jostling within the fabric gain enough energy to turn into a gas, a process that is accelerated if the material is warmer. At the same time, water molecules in the air randomly condense onto the fabric. So, the drier the air, the higher the ratio of evaporation to condensation, and the faster clothes will dry.
Warmer air holds more water, so higher temperatures reduce the relative humidity, which help clothes dry faster. A flow of fresh air carries moisture-laden air away from the drying clothes, minimising condensation back onto the fabric. So, when drying clothes indoors, pick a warm, dry room with good ventilation.
Of course, there are also some technological solutions that can speed up this process. Heated clothes airers accelerate evaporation via hot bars, while tumble dryers use a flow of warm air to heat the clothes and carry moisture away. Airers are generally cheaper to buy and run, but take longer, so for large loads, a tumble dryer may work out cheaper.
Traditional tumble dryers vent the steam they produce, while modern condenser dryers collect the evaporated moisture in a tank. Heat pump condensers are the most efficient because they recirculate warm air in the machine; but they’re also the most expensive to buy.
Drying pods are a relatively new invention; they blow hot air through clothes hanging underneath a cover. They tend to dry clothes faster than heated airers but are more expensive to buy and run.
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Asked by: Eric Pearson, via email
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Dr Claire Asher is a science journalist and has a PhD in Genetics, Ecology, and Evolution (GEE) at the University of Leeds. She also works part time as Manager of the UK Robotics and Autonomous Systems (RAS) Network, based at Imperial College London. Asher is also the author of Brave Green World: How Science Can Save Our Planet.
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