Because the design of the enclosure is non-essential to the proper functioning of your batch heater, we'll limit our discussion of this step to a general run-through of the major concepts and procedures. Only you know what type of
exterior enclosure will work best at your home, so we'll leave the specific details
of this one step to you.
Building a batch heater isn't very difficult, and if you know how to hammer, saw, and solder, the entire job should take about five weekends, tops. Your best bet is, first, to read through the following pages to get a feel for the scope of the project. As you read through the step-by-step procedures, you'll find numerous terms in italics, such as tank support bracket and involute center cleat. The italics mean that these specialized (Continued page 29)

Photo Three The mirrorlike Mylar should be handled carefully and protected with newspapers to avoid scratches. Here, one of the plywood involute patterns is about to be used as a template to cut out a section of the Mylar. Each component of the reflector should be fitted with its own individually cut piece of Mylar to allow for slight differences in size and shape.

Photo One Following the instructions in the text, it's easy to draw the correct involute and cusp for any tank using only a length of wire and a pencil. Here you can see how the curve is formed automatically as you move the pencil away from the tank. The plywood will be cut along this line to create the "involute patterns" shown in the next steps.

Photo Six When the reflector subassembly is complete, it's enclosed in a simple but sturdy framework of 2 X 4s. Truss plates (the worker is nailing one in place), joist hangers, and plumber's straps help reinforce the frame's joints, making sure it safely can carry the full 500-plus-pound weight of the filled water tank.

Photo Two The "flashing layout line" will help you mount aluminum flashing
to form the sharp point of the cusp. Simply place a scrap of flashing at the
point of the cusp, bend it slightly to follow the curve of the involute, and
make a pencil mark where the flashing ends. We'll refer to this mark in a later
step.

Photo Four The involute pattern is the keystone of the reflector assembly. Here, auxiliary fittings are added: A top cleat (the long board) provides a place to fasten other pieces of the reflector frame. Two bracket cleats (the identical short boards) help support the water tank in a later step. And the center cleat (the triangular board) will help hold the reflector center support in place.

Photo Five After the cleats are added,
the reflector side boards are nailed to
the plywood patterns, forming the
rectangular assembly shown, on the
floor. The workers are setting a "V"
shaped assembly of hardboard sheets
and a 2 X 2-inch, center support into the
points of the involute pattern's cusps.
In the next step, the hardboard sheets
will be bent downward to follow the
curves of the involute patterns, finishing the reflector subassembly.