How to Install a Solar Heater in Your Pool

One of the most logical uses of solar energy is to heat a home swimming pool, since sunshine and swimming weather are so closely linked. The simplest and least expensive way to warm an unheated pool with sunrays, or to ease the load on a gas or electric pool heater, is to cover the water with a transparent plastic blan­ket, commonly made of heavy, double-thickness polyethylene.
By preventing evaporation (which can account for up to 55 percent of a pool’s heat loss) while still permitting sunlight to warm the wa­ter, a plastic cover can raise the tempera­ture of a pool by as much as 10° F. on a sunny day. Used in conjunction with a conventional heater, a pool blanket can pay for itself over a single season in re­duced energy bills.

But full-fledged solar systems, available from solar equipment-dealers and from some pool-supply stores, are even more effective. Most pools are heated to around 80° F; in warm weather, a solar system can do the job unaided by a stan­dard gas or electric heater. In cooler weather it can save considerable energy by preheating the water before it passes into the conventional heater.

Because the basic plumbing necessary to circulate the water through the solar collector panels is already included in the pool’s filter system, a solar heating loop need only tap into the existing pipes- usually at a point just beyond the filter but before the conventional heater, if any.

A one-way check valve prevents wa­ter from draining back into the filter from the elevated collectors, and a manual or thermostatically-controlled gate valve al­lows pool water to bypass the solar heat­er on cloudy days, or whenever the pool has heated up sufficiently. The existing swimming-pool pump will often be pow­erful enough to circulate water through the panels, but the panel manufacturer or dealer may recommend that you retro­fit a larger pump.

Solar collector panels for pool heat­ing are simpler and lighter than the ones that are designed for hot-water sys­tems, requiring no insulation or glazing. Many are copper; others are merely 3-by-8-foot sheets of molded plastic, honey­combed with channels through which the water circulates.

The panels must be mounted on a roof and oriented toward the sun in the same manner as other solar collectors. If near­by south-facing roof surfaces do not pro­vide the proper angle, you can secure the panels to an inclined roof rack, but covered with %-inch plywood (the lightweight pool panels will sag in the middle if they are not supported). In many cases, however, the simplest way to mount the collectors is to build a nearby cabana-style shelter with its roof oriented due south and pitched at an angle equal­ing your latitude.

To heat the water adequately, you will need collector panels with a total surface area equal to half the area of your pool. To ease installation, use schedule-40 PVC pipe and, whenever possible, PVC valves and fittings to make the plumbing con­nections. Buy the type of pipe that is specifically labeled for outdoor use; the plastic is formulated with a stabilizer that enables it to withstand prolonged expo­sure to sunlight. The PVC pipe ordinarily used for indoor plumbing degrades rap­idly in the sun and must be painted if it is used outside the house. You can buy pipe, fittings, and any other hardware not included with the panels, at plumbing and home-improvement stores.