EPISODE · May 28, 2026 · 6 MIN
Wet Towels, Cold Rooms: The Hidden Physics of Indoor Laundry Drying - #OT45
from Air Quality Matters · host Simon Jones
This week, we dive into a fascinating full scale experimental study published in the Journal of Indoor Environments titled Indoor Laundry Drying: Full Scale Determination of Water Emissions Rates and Impact on Thermal Comfort, to explore a question that fundamentally challenges how we think about energy efficiency advice: What if the single most common energy saving recommendation—drying clothes indoors instead of using a tumble dryer—is actually forcing us to turn up the heating and creating serious indoor air quality problems we've never properly quantified? Across Europe, particularly during winter months, over 60% of laundries are dried indoors in countries like Poland, Hungary, Czech Republic, and Finland. In France alone, tumble dryers account for 20% of average annual household electricity consumption. The advice is clear: save energy, ditch the dryer, hang your clothes on a rack. But while we know this practice coincides with dust mite growth and high concentrations of airborne mould spores due to rising moisture, the actual kinetics—how much water is emitted, exactly when, and how it physically changes the room's environment—has never been properly quantified in a controlled, full scale way. Until now. Key Topics Discussed: The Cotton Culprit: A typical four kilogram load of dry cotton towels will hold about two litres of water after a standard 40 degree wash. Spinning faster than 1,000 RPM doesn't extract much more water. Cotton is the real moisture problem when it comes to indoor drying. Three Phases of Drying: By constantly weighing the drying rack and monitoring room humidity in a controlled 40 cubic metre experimental chamber, researchers discovered water emission isn't a slow, steady trickle. It happens in three distinct phases: the initial burst (first two hours, exceeding 100 grams per hour, peaking at 360 grams per hour), the steady state (10 to 25 hours, stabilizing around 50 grams per hour as the room becomes humid), and the exhaustion phase (beyond 30 hours, gradually tailing off). The Temperature Drop Problem: Evaporating water is endothermic—it literally sucks heat out of surrounding air. As laundry dried, room temperature dropped significantly, recording drops between half a degree and 3.8 degrees Celsius. If your room starts off quite dry, the initial humidity gradient is higher, water evaporates faster, and the temperature drop is even sharper. The Thermal Comfort Failure: When researchers mapped these temperature and humidity changes onto standard thermal comfort charts like ASHRAE 55, the results were clear: passive indoor laundry drying actively drags room conditions right out of acceptable comfort zones. Even wearing thicker winter clothes only partially mitigates the discomfort. The Heating Paradox: If we're told to avoid tumble dryers to save energy, but doing so drops the temperature of our living spaces by almost four degrees, what do we inevitably do? We turn up the central heating. The energy saving advice creates a new energy consumption problem. Mitigation Strategies: We need to be strategic about where we dry clothes. Positioning drying racks in bathrooms close to air extraction points can avoid spreading moisture and physically cooling down living and sleeping spaces. The first hour or two of clothes drying is particularly critical for moisture emission. Indoor laundry drying: Full-scale determination of water emission rate and impact on thermal comfort https://doi.org/10.1016/j.indenv.2025.100089 The Air Quality Matters Podcast in Partnership with Particles Plus https://particlesplus.com/ Eurovent (https://www.eurovent.eu/) - Aico (https://www.aico.co.uk/) - Lindab (https://www.lindab.ie/) The One Take Podcast in Partnership with SafeTraces (https://www.safetraces.com/) and Inbiot (https://www.inbiot.es/?utm_campaign=simon&utm_source=airqualitymatters&utm_medium=podcast) - Farmwood (https://farmwood.co.uk/) Do check them out in the links and on the Air Quality Matters Website. (https://www.airqualitymatters.net/podcast) If you haven't checked out the YouTube channel its here (https://www.youtube.com/@airqualitymatters-SimonJones). Do subscribe if you can, lots more content is coming soon. Chapters 00:00:00 Introduction: The One Take Format and the Mundane Routine of Laundry 00:00:58 The Energy Paradox: Why We're Told to Ditch the Tumble Dryer 00:02:21 The Cotton Culprit: How Much Water Are We Really Releasing? 00:03:03 The Three Phases of Drying: From Burst to Exhaustion 00:04:04 The Endothermic Effect: Why Drying Clothes Literally Cools Your Room 00:04:40 The Thermal Comfort Crisis: When Laundry Drags You Out of the Comfort Zone 00:05:04 The Heating Trap: Trading Tumble Dryer Energy for Central Heating 00:05:26 The Strategic Solution: Building Physics Meets Laundry Day 00:06:01 Closing Thoughts: Treating Mundane Tasks with Building Physics Respect
What this episode covers
This week, we dive into a fascinating full scale experimental study published in the Journal of Indoor Environments titled Indoor Laundry Drying: Full Scale Determination of Water Emissions Rates and Impact on Thermal Comfort, to explore a question that fundamentally challenges how we think about energy efficiency advice: What if the single most common energy saving recommendation—drying clothes indoors instead of using a tumble dryer—is actually forcing us to turn up the heating and creating serious indoor air quality problems we've never properly quantified? Across Europe, particularly during winter months, over 60% of laundries are dried indoors in countries like Poland, Hungary, Czech Republic, and Finland. In France alone, tumble dryers account for 20% of average annual household electricity consumption. The advice is clear: save energy, ditch the dryer, hang your clothes on a rack. But while we know this practice coincides with dust mite growth and high concentrations of airborne mould spores due to rising moisture, the actual kinetics—how much water is emitted, exactly when, and how it physically changes the room's environment—has never been properly quantified in a controlled, full scale way. Until now. Key Topics Discussed: The Cotton Culprit: A typical four kilogram load of dry cotton towels will hold about two litres of water after a standard 40 degree wash. Spinning faster than 1,000 RPM doesn't extract much more water. Cotton is the real moisture problem when it comes to indoor drying. Three Phases of Drying: By constantly weighing the drying rack and monitoring room humidity in a controlled 40 cubic metre experimental chamber, researchers discovered water emission isn't a slow, steady trickle. It happens in three distinct phases: the initial burst (first two hours, exceeding 100 grams per hour, peaking at 360 grams per hour), the steady state (10 to 25 hours, stabilizing around 50 grams per hour as the room becomes humid), and the exhaustion phase (beyond 30 hours, gradually tailing off). The Temperature Drop Problem: Evaporating water is endothermic—it literally sucks heat out of surrounding air. As laundry dried, room temperature dropped significantly, recording drops between half a degree and 3.8 degrees Celsius. If your room starts off quite dry, the initial humidity gradient is higher, water evaporates faster, and the temperature drop is even sharper. The Thermal Comfort Failure: When researchers mapped these temperature and humidity changes onto standard thermal comfort charts like ASHRAE 55, the results were clear: passive indoor laundry drying actively drags room conditions right out of acceptable comfort zones. Even wearing thicker winter clothes only partially mitigates the discomfort. The Heating Paradox: If we're told to avoid tumble dryers to save energy, but doing so drops the temperature of our living spaces by almost four degrees, what do we inevitably do? We turn up the central heating. The energy saving advice creates a new energy consumption problem. Mitigation Strategies: We need to be strategic about where we dry clothes. Positioning drying racks in bathrooms close to air extraction points can avoid spreading moisture and physically cooling down living and sleeping spaces. The first hour or two of clothes drying is particularly critical for moisture emission. Indoor laundry drying: Full-scale determination of water emission rate and impact on thermal comfort https://doi.org/10.1016/j.indenv.2025.100089 The Air Quality Matters Podcast in Partnership with Particles Plus https://particlesplus.com/ Eurovent (https://www.eurovent.eu/) - Aico (https://www.aico.co.uk/) - Lindab (https://www.lindab.ie/) The One Take Podcast in Partnership with SafeTraces (https://www.safetraces.com/) and Inbiot (https://www.inbiot.es/?utm_campaign=simon&utm_source=airqualitymatters&utm_medium=podcast) - Farmwood (https://farmwood.co.uk/) Do check them out in the links and on the Air Quality Matters Website. (https://www.airqualitymatters.net/podcast) If you haven't checked out the YouTube channel its here (https://www.youtube.com/@airqualitymatters-SimonJones). Do subscribe if you can, lots more content is coming soon. Chapters 00:00:00 Introduction: The One Take Format and the Mundane Routine of Laundry 00:00:58 The Energy Paradox: Why We're Told to Ditch the Tumble Dryer 00:02:21 The Cotton Culprit: How Much Water Are We Really Releasing? 00:03:03 The Three Phases of Drying: From Burst to Exhaustion 00:04:04 The Endothermic Effect: Why Drying Clothes Literally Cools Your Room 00:04:40 The Thermal Comfort Crisis: When Laundry Drags You Out of the Comfort Zone 00:05:04 The Heating Trap: Trading Tumble Dryer Energy for Central Heating 00:05:26 The Strategic Solution: Building Physics Meets Laundry Day 00:06:01 Closing Thoughts: Treating Mundane Tasks with Building Physics Respect
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Wet Towels, Cold Rooms: The Hidden Physics of Indoor Laundry Drying - #OT45
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