Window trickle ventilators - holes are drilled with the window frame, with exterior and internal handles above the holes. A cheap but visually intrusive system, with poorer Vitality performance than other solutions. And in the summertime? They keep the warmth out, so your AC is not chugging along all day. https://exteriorpostlight10627.blog-ezine.com/34995173/5-simple-techniques-for-double-glazing