In most climates, the water in a swimming pool must be heated to make it comfortable for swimming. The plumbing involved is the same for all methods of pool heating: water from the pool is filtered, pumped through a system of piping where heat is transferred to the water, and the water is then returned to the pool. Above ground pool heaters and inground pool heaters are essentially the same, though above ground pools are susceptible to more energy loss, so they may need more heat input.
Natural gas or propane heaters continue to be the most popular choice for swimming pool heating. They allow you the most control over the temperature of the pool water, and they will heat the water quickly. They are also the least expensive to install. However, they will be the most expensive to operate, and require regular maintenance.
These heaters consist of loops of copper tubing which are heated by a direct flame. Heat transfers to the water flowing through the tubing.
Solar pool heating takes advantage of a free resource: the sun. In climates where the weather is extremely hot, the water can even be circulated through a solar system at night in order to cool it. The drawbacks of solar pool heaters include the initial installation price and a low amount of control over the actual water temperature. One must also consider where the solar panel can be installed.
Solar pool heating systems are fairly simple. The water flows through multiple loops of tubing which absorb solar heat. The more temperate the climate, the more complex and expensive the system becomes. However, solar pool heater systems last the longest and are very-low maintenance, but the water temperature cannot be changed quickly.
A swimming pool heat pump works the same way as a refrigerator: it simply moves heat from one place to another. A fan pulls air over an evaporator coil filled with a liquid that pulls heat from the air and transfers it to the water.
Heat pumps will work when the outside air is warmer than 45 degrees Fahrenheit. Though they are expensive to install, they are extremely efficient. Heat pumps also change the pool temperature slowly, allowing you more control over how hot the water is.