Overview

• Opening windows when outside temperatures exceed indoors can trap heat and prompt heavier fan or cooling use that drives up energy bills.
• Experts advise closing windows, blinds and curtains during peak sun hours—typically 11am to 3pm—to prevent solar heat gain in south- and west-facing rooms.
• They recommend opening windows between about 9pm and 5am or during early morning and late evening to draw in cooler air and using fans to boost circulation.
• Homes with large or single-pane glazing and minimal shading are especially prone to a greenhouse effect, radiating heat back into living spaces.
• Low-cost measures such as thermal blinds, hanging a damp sheet and unplugging heat-emitting appliances offer affordable ways to cool homes without extra bills.