There is a system in ventilation fan called the heat exchange system. When the window is closed, the wind coming in from the outdoor air duct through the ventilation fan will be heated by the heat exchange system to heat the air into the room;
Wall-mounted fans and wall-type fans eliminate the need for layout ventilation ducts, and the overall footprint of the house is very small, which does not require a lot of engineering design, thus saving more time and space.
In fact, this surprise like my friend is not surprising. This is the reason why the awareness of fresh air is not strong, so many consumers of the Wall mounted fan are still in the stage of doubt. In fact, at this point, the state has already had a slight political problem with regard to environmental protection.