Solar Covers: Heat Retention During the Swimming Season
Solar covers — also called bubble covers or solar blankets — are lightweight polyethylene covers with a bubble surface that traps solar energy and transfers heat to pool water. Their primary function is heat retention overnight: a pool that reaches 82°F during the day can drop 5–10°F overnight without a cover, depending on humidity and ambient temperature. A solar cover limits that overnight loss to 1–2°F, reducing heater run time and energy cost significantly.
Solar covers also reduce evaporation by approximately 95% when in place. Evaporation is the primary mechanism of heat loss from an outdoor pool — when water evaporates, it carries heat with it. Reducing evaporation reduces both heat loss and water loss, meaning fewer fill additions and more stable chemistry. A pool without a cover can lose one inch of water per week to evaporation during a warm Boston summer; with a solar cover in place during non-swim hours, that loss drops to nearly zero.