This app calculates the Dew Point based on temperature and relative humidity.
Tap the thermometers and simply adjust the values for relative air humidity and air temperature. The dew point and the absolute water content of the air are calculated automatically. The dew point tells you, at which temperature of e.g. surfaces, walls or window panes condensation starts.
So: Walls which have a lower temperature than what the dew point tells you, get wet! Window panes get fogged.
Make sure, that humidity is sufficient low and the walls are adequately warm.