Many people think that a sliding window ventilates better than a hinged window, butventilation is not about the direction that the opening faces, think for example, about a draft that you might feel in your home, it’s not easy to find the source, in fact it may not be visible. The air doesn’t care about the shape or location of an opening becausetrue ventilation is achieved by pressure difference, NOT window style. So how does this ventilation pressure difference happen? Let’s take a house that faces the breeze and has windows open into the breeze at the front and at the back the windows face away from the wind. It’s obvious that the windows facing the breeze will have positive pressure against the opening and the breeze will naturally gain access – regardless of the position of the opening. Now, at the rear of the house, the breeze blows over the house and past the open windows, this causes a negative pressure and sucks air out of the home, this is known as the Venturi effect. (discovered by Italian physicist Giovanni Battista Venturi 1746-1822). The same effect occurs along the sides of the house, sucking air from open windows, leaving the inside space to naturally ventilate using convection.
Further, regarding the sliding window, would you leave your sliding window open in the rain? No, because the rain will enter the exposed opening. But you can leave an awing window open and the rain is kept out because the opening is sheltered by design.