Overview
- Recent coverage on June 22 and 23 consolidated official guidance saying fully lowered shutters can trap hot air between the shutter and pane and push heat into the room.
- The trapped-air effect occurs when solar radiation heats the air in the gap and the warm air transfers heat to the glass, which then radiates into the interior.
- Practical advice is to keep external shading in place while leaving small light or ventilation slits in lowered shutters so air can circulate without exposing the glass to direct sun.
- Ventilate at night or in the early morning when outside air is cooler to cool rooms, and use short daytime shock-ventilation when people are present to remove humidity and CO2.
- Authorities recommend outside-mounted shading plus timed ventilation as the most energy-efficient strategy to limit overheating and reduce risks of mold or physical damage to windows and shutters.