Double glazed windows will be airtight, compared to single glazed windows. For this reason, condensation can build up in your house, because of the reduced ventilation.

If there is not an ample level of background ventilation in the room, it is common that some replacement windows will have trickle vents incorporated into the frame. This lets in a small amount of controlled ventilation.

As a result, condensation can also occur – on the outside of the new double- glazed window. This is because the glass reflects heat back into the home, which keeps the outside pane cool. In this scenario, condensation can build up in cold weather. This isn't a problem.