There are several ways to heat a pool, but the cheapest method will depend on several factors, such as the size of your pool, the location, and the climate. Here are a few options that can be relatively inexpensive:
Solar covers: Solar covers can help to trap heat from the sun, which can help to raise the temperature of your pool. They also help to reduce evaporation and keep debris out of the pool.
Solar heating panels: Solar heating panels can be installed on the roof or on the ground, these panels use the sun's energy to heat the water, which is then circulated back into the pool.
Heat pump: A heat pump works by extracting heat from the air and transferring it to the pool water. It can be more efficient than electric heaters and can be cheaper to operate.
Gas pool heaters: Gas pool heaters are powered by propane or natural gas, they can heat the water quickly and effectively, but they can be expensive to operate.
Electric pool heaters: Electric pool heaters can be cheaper to install than gas heaters, but they can be expensive to operate due to the cost of electricity.
It's important to note that the cheapest method will depend on your individual circumstances, such as the cost of electricity and gas in your area and the size of your pool. It's a good idea to consult with a professional pool service or pool equipment supplier to determine the best and most cost-effective heating solution for your pool.