But according to glazing expert Antony Heath from Glevum Windows , opening windows during the hottest part of the day can actually allow more hot air into a property, increasing indoor temperatures and making homes less comfortable. "If the temperature outside is higher than it is indoors, opening windows can allow more hot air into the home and push indoor temperatures up even further. Opening windows during peak afternoon temperaturesIf the air outside is warmer than the air inside, opening windows can simply allow more heat into your home. Forgetting to create cross-ventilationWhen temperatures begin to drop later in the day, opening windows on opposite sides of the property can help fresh air flow through the home and remove trapped heat. Opening windows on both lower and upper floors can help encourage hot air to escape more effectively.