The article "The Solar System" in the April 9 issue has several incorrect and misleading statements and ends on a totally false premise that, if credible, could frighten away potential buyers.

The article mentions costs to consumers for "average size" systems. We avoid giving dollar amounts because labor and overhead costs vary widely throughout the country. We tell a dealer that they should expect to be able to install the average solar system, located close to the pool, with two installers in one day. We have many experienced dealers who routinely install six-panel systems with two men in one-half day.

On page 74, a paragraph begins with, "Much of solar system repair work is warranty-related ..." This entire paragraph appears to be illogical and not in accordance with our observations.

The caption below the controller photograph states: "The controller ... uses the information to know when it is time to release heated water from the roof into the pool." That statement appears to support the misconception we hear from some nontechnical people that the solar collectors are filled with water that is released to the pool when it gets hot. Actually, solar collectors are most efficient when they operate at low temperatures. Therefore, we try to send the maximum amount of water through the collectors, discharging it into the pool a few degrees above pool temperature. That sends the maximum amount of heat, measured in BTUs, to the pool.

The following appears on page 76: "... the water then circulates through an array of small tubes within them (located behind the glass) and warms up in the sun." However, a solar collector with no glazing puts more heat into the water during the swimming season than does a glazed collector. Since 1979 or so, nearly all solar collectors heating pools have been unglazed.

Incidentally, all of the illustrations accompanying your article show unglazed collectors. In the same column on page 76, the following appears: "Polypropylene ... a plastic known for its resistance to degradation caused by UV rays and harsh pool chemicals, has be come the preferred material for the solar industry." Generally, true, except that all accompanying illustrations show copper collectors. Accurate data are not available, but we estimate that copper collectors represent less than 3 percent of the solar pool heaters produced.

The article's solar system diagram shows the solar sensor in contact with the solar collector. That will cause the solar control to short-cycle and the solar system will not heat the pool The solar sensor should see the same amount of sun that the collectors see, but it must never contact the surface of a collector or a system pipe.

Pump sizing is addressed on page 78. We design both our polypropylene panel collectors and our mat collectors to have low pressure losses. We use generously sized, straight-through absorber water passages and 2-inch inside diameter headers. We recommend connecting the solar system to the circulation system with 2-inch schedule 40 PVC pipe, using a minimum number of fittings. Simply by following these directions, the installer will find that almost any modern pool pump that was properly sized to carry the filtration load will easily handle the added solar system load.

The last paragraph in the article claims that vacuum relief valves eventually fail and when they do, they can cause the water to boil and burst the tubes. The troth is that it is physically impossible for that to happen on a functional solar pool beating system. We use two types of vacuum relief valves, one of them since 1978. The only failures I have seen were caused by foreign material, usually sand or DE, holding the valve open. That would vent pressure, having the opposite effect from the one described. Even if a valve were to fail in the closed position, pressure cannot build up because the return pipe from the solar system to the pool is open to the pool In addition, we use a nonpositive shut-off control valve that vents the system at the inlet end.

You have an excellent publication and I would like to assure your readers that solar systems are user-friendly, easy to install and are not limited to rooftop installation.