Damp, Mould and Humidity Tools
Condensation, black mould and musty rooms all come down to moisture in the air meeting a cold surface. These tools show where the risk is, what humidity keeps a room dry, and which dehumidifier would help.
Two free tools. No sign-up, nothing stored about you, and every result shows how it was worked out.
Damp & Air
The tools
Dehumidifier Picker
Find the right dehumidifier size and type for your room.
Damp & Mould Check
Check whether a window or wall will get condensation or mould, and what humidity keeps it dry.
Which tool do I need?
Find the right tool
- To check whether a window, wall or corner will get condensation or mould, use the Dew Point & Mould Calculator.
- To find the right size and type of dehumidifier for a room, use the Dehumidifier Picker.
- To see what a dehumidifier or heater costs to run, use the Electricity Cost Calculator.
- To find out how much heat a cold wall loses, use the U-Value Calculator.
Good to know
Before you start
Aim for 40–60% humidity
Mould grows when a surface stays above about 80% humidity for days. Keeping the room between 40 and 60% usually keeps cold spots below that.
Cold spots first
Condensation forms on the coldest surface: single glazing, window reveals, corners of outside walls and behind wardrobes. Check those with a cheap hygrometer.
When to call someone
Damp low on a wall, a tide mark or damp after rain usually means water getting in, not condensation. A dehumidifier won't fix a leak or rising damp.
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