Whether you need a heater for your above-ground swimming pool depends on where you live and your preferences. In hot climates, the sun and high temperatures are usually enough to keep your pool at a comfortable swimming temperature. However, if you live in a cooler climate, the water in your pool may not always reach a temperature that's comfortable for you. In such a case, a heater would greatly benefit you -- and extend your swimming season. The most common above-ground pool heaters are solar pool heaters, gas pool heaters and heat pumps.
Solar pool heaters use the sun's energy to heat your water. They cost a few thousand dollars and are most effective in areas with a lot of sun; solar pool heaters need about four to six hours of direct sunlight per day to heat a pool. They work using solar panels; after your filter cleans the water, a pump then sends the water through the panels to heat up and then directs it back into the pool. You can also use a solar blanket to cover your pool when you're not using it; this will take advantage of any sunlight available to keep the water below the blanket at a comfortable temperature.
Gas pool heaters burn gas to quickly heat your pool; they don't usually have to run very long before the pool is warmed. The cost of running a gas heater depends on what your utility company charges. Meanwhile, electric pool heaters work the same way, but they use electricity instead of gas and typically require more time (and power) to heat a pool. Electric heat pumps extract heat from the air in your backyard and then pump it into the water. Like solar heaters, heat pumps are considered to be environmentally friendly.