Heatwave puzzle solution: curtains and blinds block 67 percent of sun’s energy
7 reported
The Guardian published a puzzle about keeping homes cool in a heatwave, asking readers to calculate the percentage of the sun's energy that enters a room with both roller blinds and curtains. The solution, provided by puzzle contributor Alan Williams-Key, is 33 percent. The puzzle assumes the blinds and curtains are made of homogeneous material, the system has reached equilibrium, and factors like glass windows, material color, and room shape are ignored. The explanation involves heat flow between the curtain and blind layers, with the curtain radiating half its absorbed heat back toward the window and half into the room. The blind radiates energy both forward and backward, and after accounting for heat exchange between the two layers, only one-third of the sun's energy reaches the room. The article notes that this is a simplified model.
What’s reported
The puzzle was set earlier on July 20, 2026, and the solution was provided in the same article.
The scenario involves a room with roller blinds covering windows and curtains covering the blinds.
The solution states that 33 percent of the sun's energy gets into the room.
The curtain radiates 50 percent of absorbed heat back toward the window and 50 percent into the room.
The blind radiates energy in both directions, and the curtain also radiates heat back to the blind.
The puzzle was contributed by Alan Williams-Key.
The puzzle is part of a series set on alternate Mondays since 2015.
Key figures
Alan Williams-Key: puzzle contributor
Sources: The Guardian
