While they may not be strictly necessary, a good swimming pool heating system can add months to the length of time you can safely use your pool, although how much time depends on which system you use and what the climate is like where you live. If it’s always sunny and temperate, then there may be no point at all in getting a heating system, but if it drops below freezing for half the year then you’ll need either a powerful heater or else the patience to wait six months before using your pool again.
There are three primary methods to heating a pool: solar, electric, and gas.
Electric heaters are neither as cheap as solar nor as effective as gas.
Electricity is pretty effective at providing heat for a pool, although you do have to pay your utility company for the energy. A decent electric heater can keep a pool at a safe temperature even on days as cold as 45 degrees Fahrenheit, long past what a solar heater could manage. However, the electric heater requires regular maintenance and repair, and its lifespan is only around 5-10 years.
Gas heaters are extremely effective at providing heat, but they can be expensive, whether you use natural gas or propane.
Natural gas and propane both burn at exceptionally hot temperatures, and so they can heat your pool in a hurry even in freezing weather. Gas heaters are best for when you intend to use your pool all year round no matter what, or else as a way to keep a hot tub warm.
Still, the high operating temperature means the heater needs constant maintenance and will only last around 5 years at best.
The advantage of solar power is cost, but the disadvantage is efficiency and ungainly panels on your roof.
While regular solar panels turn the sun’s energy into electricity, solar pool heaters simply concentrate the heat of the day onto the pool water as it’s pumped up onto your roof, through all the cells, and then back down again. Solar power can add several degrees to your pool’s temperature, but it all depends on how much sunlight you get. One dreary day can completely drop the pool’s temperature down to ambient levels.
On the plus side, though, the solar pump doesn’t use much energy and the sun’s rays are free. Solar panels also don’t need much maintenance, and they can easily last up to 20 years.
With all that in mind, it’s clear enough that solar power is best where it’s sunny and warm for most of the year, electric heaters are better farther north, and gas is only useful sparingly or for small pools and spas. In all three cases, though, you should always get a thermal pool cover. Trapping the pool’s heat will double your heater’s effectiveness no matter which kind you use.