The open window, done right
Heatwaves, condensation, mold, humidity — the physics of a cooler, drier home, in plain words.
The Morning Rule: When to Shut Everything
On hot days there is one moment when open windows start heating your home. How to spot the crossover and lock the night's coolness inside.
Why Humid Heat Feels So Much Hotter
28 °C can feel pleasant or unbearable depending on how much water the air carries. The physics of sweat, and why dew point beats the humidity %.
Thermal Inertia: Why Stone Homes Stay Cool
Why old stone houses stay cool through July afternoons while modern flats overheat by noon — and how to work with your walls, not against them.
Roof Windows and the Stack Effect
Warm air rises. A roof window turns your home into a gentle chimney that flushes heat out even without wind. How the stack effect works.
The 3 PM “Dry Air” Trap
Afternoon air at 35% humidity often holds more water than morning air at 90%. Why relative humidity tricks you into airing at the worst hour.
Keeping Your Home Cool in a Heatwave, No AC
A home can stay livable through a heatwave without AC — if the timing is right. Shut and shade by day, flush at night, and watch the humidity.
Shutters, Blinds, Curtains: What Blocks Heat?
Sunlight that passes the glass becomes heat you cannot send back out. Why exterior shutters beat any curtain, and what still helps if you rent.
Get Your Home Summer-Ready: A Checklist
The first heatwave is won in May, not in July. A practical checklist — shading, airflow paths, night routine — to prepare your home before the heat.
The Best Bedroom Temperature for Sleep
Around 17–19 °C is commonly recommended for sleep, but humidity decides how the night actually feels. How to get your bedroom there without AC.
Cooking Without Steaming Up Your Home
Every pot that boils pushes water vapour into your air. Where cooking steam actually goes, and how lids, hoods and smart airing keep your home dry.
How Much Water Vapour Does a Home Produce?
Breathing, cooking, showers and laundry release litres of water vapour every day. Where it all goes, and why it has to be ventilated out.
Spring Airing: Fresh Air vs Pollen
How to air your home in pollen season: when pollen pressure is lower, and why short cross-draft bursts beat a window left open all day.
Ideal Indoor Humidity: What 40–60% Really Means
The 40–60% indoor humidity rule explained: why the number moves with temperature, and how to steer your home back into the comfort zone.
Shower Steam: Beating Bathroom Condensation
Why your bathroom fogs up after a shower, and how dew point, door discipline and short intense airing keep condensation and mold away.
Why a Tilted Window Barely Ventilates
A tilted window swaps far less air than you think. Here is why tilt ventilation fails, what it costs in winter, and what works instead.
Drying Laundry Indoors Without the Mold
A load of wet laundry releases litres of water into your air. How to dry clothes indoors without feeding condensation and mold.
Mold in the Bedroom: An Airing Routine That Works
You exhale water all night and cold bedroom walls collect it. A simple morning airing routine that keeps mold out of your bedroom for good.
Does Airing in Winter Waste Heat?
Most of your home's warmth is stored in walls and furniture, not in the air. Why short winter airing costs far less heat than you think.
Stoßlüften: The German Art of Airing
Shock ventilation swaps stale humid air in 5–10 minutes without cooling your walls. How Stoßlüften works, and why it beats a tilted window.
Condensation on Windows: The Real Cause
Window condensation isn't a window problem — it's humid indoor air meeting a surface colder than its dew point. Here's how to stop it.
The Magnus Formula, Explained Simply
The short formula that turns temperature and relative humidity into real water content — walked through step by step, with one honest example.
Why Your Home Feels Damp in Autumn
Clammy rooms, misted windows, musty smells: why autumn makes homes feel damp, what is actually happening, and the airing routine that fixes it.
How Long Should You Air a Room?
Five minutes or an hour? How long airing really takes by season and window setup, and why short and wide beats long and timid.
Dew Point, Explained Simply
What the dew point actually measures, why cold surfaces get wet, and how one temperature beats relative humidity for reading the air.
Cross-Ventilation: Make the Draft Work for You
Why two openings on opposite sides beat one wide-open window, how wind and the stack effect drive the flow, and when a cross-draft helps.
Window Fan Direction: Blow In or Out?
A window fan pointed the wrong way can heat your home. When to blow in, when to blow out, and how to build a two-window push-pull setup.
Why Your Bedroom Is Still an Oven at Midnight
Outside it's cool, inside you're sweating. Your walls stored the day's heat and are giving it back — here's how to break the cycle.
Relative vs Absolute Humidity, Explained
Relative humidity says how full the air is, not how much water it holds. Why that difference decides the right moment to air your home.
Does Opening Windows at Night Really Cool Your Home?
Night airing works, but only if you do it right: real airflow, the right hours, and shutting everything before the morning heat returns.
Should You Open Windows During a Heatwave?
Opening windows in a heatwave can make your home hotter and damper. Here is the simple two-number rule for when to open and when to shut.