In 2001, data collected by the U.S. Energy Information Administration indicated that heaters used in hot tubs, spas, and pools accounted for approximately 2,300 kWh of electrical use per household annually. That added up to a combined 7.6 billion kWh in the approximately 3.3 million households where the units were present. At the current national average cost of electricity ($.12 per kWh), that's about $276 per year, per household. Since it's safe to assume that the number of hot tubs, spas, and pools in the country has increased over the last decade, that's a staggering amount of dollars and power going toward heating water.

Solar pool heaters, which are easily priced competitive with gas and heat pump units, can substantially reduce energy use in this area while lowering power bills and offering fewer maintenance issues. Unlike the photovoltaic cells with which most consumers are familiar, solar pool heaters use a thermal solar configuration. Basically, water from the pool passes through a filter to remove debris before circulating through a solar collector where heating occurs. A pump circulates the water, which is diverted back to the pool itself with a manual or automatic flow-control valve. The most sophisticated units include temperature sensing devices that only circulate the water when heating to maintain a pre-determined temperature is required.

These solar systems come in either glazed or unglazed models. Unglazed units work best in regions where the temperature stays above freezing. They consist of heavy-duty rubber or plastic tubing treated with chemicals to withstand ultraviolet light. Glazed systems are protected by an iron-tempered glass covering and are made of copper tubing mounted on an aluminum plate. Equipped with heat exchangers and transfer fluids, these systems capture heat more efficiently during cold weather, but can also be used year round in most climates. They are more expensive, but can also be adapted for domestic water heating. (Note that both types of systems should include freeze protection in given regions.)

Estimated cost of the components and their installation is $3,000 to $4,000 with an expected payback on the investment in 1.5 to 7 years depending on location and annual electrical rates. The systems are largely maintenance free. Washing to maximize heat penetration is recommended and homeowners should consider the caveat that any pump or pipe can become clogged by debris if the system's filter is breached.

Homeowners interested in solar pool heaters should evaluate their site to ensure that a collector can be placed at the correct angle relative to their longitude and latitude to receive optimum sun. Most likely working in concert with a professional, determine how large the collector should be and investigate relevant local building codes and homeowner's association covenants before proceeding. The estimated operational life for a solar pool heater is 10 to 20 years, offering an excellent long-term return on the investment in both material costs and annual energy savings.