If windows have openings at both the top and the bottom (such as sash windows), using just the top opening will help incoming fresh air warm up as it mixes with room air, reducing cold draughts.
Opening windows and doors at opposite sides of your room or home will also provide a good flow of fresh air (this is known as cross ventilation).
Make sure trickle vents (small vents usually on the top of a window) or grilles are open and not blocked.
Air which flows in from these vents will mix with warm room air as it enters, which helps keep the room a comfortable temperature.
If possible, maintain openings throughout the day to allow a constant flow of fresh air into the home.
The weather can affect the amount of air that flows through openings and so these should be adjusted to balance warmth with the amount of ventilation, where possible….
Ventilation can also be increased by leaving extractor fans in bathrooms, toilets and kitchen areas running for longer than usual, with the door closed, after someone has been in the room.