How does a solar pool heating system replace a gas heater if it can't heat as quickly?


Most gas heaters are sized to (re)heat a pool in a "spot heating" mode rather than a "maintenance" mode. Spot heating refers to the practice of heating only for a short periods of time, i.e.: a weekend, or a special occasion - such as a pool party. Maintenance heating refers to the practice of leaving the heater on to maintain the desired temperature all of the time. The reason for using a "spot heating" mode is to save money. The reason for using the "maintenance" mode is to have the pool warm enough to swim in when you feel like swimming!

Solar pool heating systems are usually designed to operate as maintenance heaters. During periods of bad weather, both types of heaters aren't used. When the weather improves the solar pool heating system will bring the pool back up to swimming temperature (for free!) in about twice the time it takes the gas heater to reheat the pool (not for free!)(Also assuming that the gas heater is turned back on.)

That being said - solar pool heating systems have to be big. They start at a minimum of 50% of the pool's surface area and get larger if the condiitions are not perfect. NEVER install an undersized system - they just don't work!