Both gas and electric swimming pool heaters are effective tools to warm the water in your pool. One fairly obvious difference between them is found in their names: Gas pool heaters run on gas, whereas electric pool heaters use electricity to warm water. Other differences are in the purchase price, cost of operation, speed of heating and environmental friendliness.

Gas swimming pool heaters use gas or propane, depending on the type of heater. The ones that burn natural gas have to be hooked up to a gas line, and the ones that burn propane require propane tanks. They're particularly useful for heating up water quickly. The burning gas warms a combustion chamber, and the heat that's produced is then transferred to the pool water. Gas heaters can cost anywhere from less than $1,000 to more than $5,000, depending on the unit and the size. How much they cost to run depends on gas and propane prices. Because of the cost involved in operation and speed at which they warm water, gas heaters are typically recommended as backup heaters or for pools that don't have to be heated often.

In contrast, electric swimming pool heaters are better for extended use. They can keep the pool between 80 degrees and 90 degrees Fahrenheit (26 to 32 degrees Celsius), as long as the temperature outside is above 45 degrees Fahrenheit (7 degrees Celsius). However, they take longer to warm the water than gas pool heaters. Electric pool heaters are actually heat pumps; they extract heat from the air, transfer it to a compressor to heat it more, then pass the heat into the pool. Electric heat pumps typically run from around $2,500 to more than $4,500. However, they cost less to operate than gas pumps and are considered more environmentally friendly.