Understanding the Dilemma of Ventilation Many residents and landlords struggle with this simple question: when should you open your windows, and will it cost a lot to heat up again? It sounds funny, but it’s a real dilemma. During winter, people often hesitate to open windows because they don’t want to lose heat and waste energy. However, keeping windows closed all the time can create costly problems like poor indoor air quality (high CO2), condensation, and even mould. The T