Popenhagen says often people don’t ventilate their house at the right time, or for the right amount of time. It’s best to open the windows for 15 to 20 minutes in the middle of the day, when the air outside is at its warmest.
If you are not home during the day, then opening the windows for 5 minutes in the morning before you leave will do. Living in a damp house with condensation and mould can have a serious effect on your health.
In the bathroom you need to shut the door as soon as the bath is being run or the shower is on. Put the bathroom fan on as well and then crack the bathroom window a little. This will clear the moisture out of the room.
Don’t keep the bathroom door open while showering as the moisture will escape and travel to