Here is a basic guide to the different types of pool heaters available today:

Gas and propane pool heaters

Gas and propane pool heaters are the most common and work most rapidly. This works with natural gas if you have it, or propane tanks mounted above or below ground.

Gas heaters

Gas heaters now boast of up to 90 percent efficiency ratings and consume only as much gas as you allow. A gas heater is thermostat-controlled, so you just set it and forget it. It will also have an on/off switch, pressure switch, gas valve and high limit switches in its safety circuitry.

Gas heaters must be installed and vented properly or hazards could result.

Heat pumps

Cheaper to maintain than gas heaters, heat are a clean, economical way to extract "free heat" from the ambient air. A heat pump draws the natural warmth from the air and uses it to maintain a comfortable temperature. This is accomplished through a refrigerant vapor compression cycle that transfers heat from one source to another. It can be compared to a household air conditioning system "in reverse."

Heat pumps are commonly used from Florida to Canada and very efficient, allowing your pool to remain operational down to 50 degrees Fahrenheit.

Millions worldwide have been enjoying solar-heated swimming pools for over two decades. You will probably find that you will pay much less for a solar heater for your above-ground or small in-ground pool than for any other type of heater.

While the first solar systems for larger in-ground pools may equal or somewhat exceed those of other heaters, they return the cost difference in fuel savings in the first year or two.

Solar pool heating systems

Gaining in popularity, solar heaters are also cheaper to maintain than gas heaters and now account for about 20 percent of pool heater installations.

Solar heaters use your existing pool pump to circulate water through the many small passages of the solar collector where it is warmed by the sun. This heated water then flows directly back to your pool through your regular pool plumbing. This simple cycle continues until your pool reaches your desired temperature.

You can also cool an overheated pool in warmer months by simply running the pool pump at night.

Solar covers/solar blankets

Made from thin plastic formed with air pockets so it can float on the surface, a solar cover cannot heat a pool. It is not totally transparent to sunlight so it blocks out much of the sun's energy that would otherwise heat the pool. However, it effectively prevents evaporation from the water surface, slowing down cooling of the water at night and in bad weather.

Use of a solar cover is recommended at night on above-ground pools with a solar heater.

A solar cover or blanket will help a pool retain heat, but a solar system actually adds heat to raise the temperature of your pool water.