The coolest water in the tank will be drawn out at #5 or #7 (See Fig. 9); (preferably #7 which leaves #5 free for its intended purpose; a drain and flush) by the pump and sent to the collector. The water should enter at the lowest point of the collector and exit at the highest point.

_{Figure 9}

From the collector, the water the travels back to the top of the tank at #4, #6 or #2. Be sure to use dielectric fittings at all points where dissimilar metals are adjacent. (e.g. copper pipe to steel pipe, or copper pipe to steel tank).

_{Figure 10}

The two gate valves are useful if you want to isolate the tank from the collector loop in order to work on the pump or the collector.

The one way valve (check valve) prevents the water in the loop from thermosiphoning at night and thereby cooling off. There are two types of check valve. A spring loaded check valve can be mounted horizontally or vertically but a swing check valve must be mounted horizontally and with the cap side up. Be sure the arrow points to the direction of normal (pumped) flow.

A pressure relief valve (T & P valve) on the collector, separate from the T & P valve on the tank, is necessary as a safety measure when the two gate valves are closed and the collector is isolated. Be sure to vent this T & P valve outside or to a drain or container.

The drain at the low point of the loop simplifies things if maintenance is necessary or for occasional purging of sediment if the collector draws from #5.

The Big Fins fall to a temperature between the inside temperature and the outside. A few observations at dawn during cold weather with an IR scanner or a thermometer attached to a fin, will give for a good idea of how much cold outdoor temperatures draw down the Big Fin temperatures. The lowest spot on the Big Fin is probably the coldest.

Remember, a line ruptured by freezing will not leak until later when the ice thaws (when you are perhaps away from the house).

An electric element can be fitted to permit flow to or from the absorber by using a nipple and a T with water entering or leaving through the T.

Photovoltaic pumps for circulation are not that much more expensive than A.C., and require no controls and work with or without line power.

The pump which circulates the water through the collector and back to the tank is turned on and off automatically by the solid state control (See Fig. 11). The control reads the temperatures of the collector and of the tank. When the collector becomes 20º hotter than the tank, it will turn on the pump. When this temperature difference falls to 5º, it will turn the pump off.

Install the control package according to the instructions packed with it.

_{Figure 11}

The sensor for the collector should be mounted on the back of a fin close to the hot water outlet. Mount it behind an area of the fin which is not shaded. Attach to the fin with a sheet metal screw and insulate the back of the sensor.

The sensor on the tank should be mounted low on the tank, under the insulation, on the steel surface of the tank itself (not the jacket). It can be attached with foil-backed tape, epoxy, or a clamp.

Follow the instructions packed with the pump for installation and lubrication.