How to Convert a Water Heater to a Solar Closed Loop

Solar water heaters, or thermosiphons, are passive solar devices. This means that a thermosiphon will heat your water without using electricity or fuel. By using an old hot water heater for a storage tank, you save yourself time and money. The insulation on the tank will also help your thermosiphon to function more efficiently.

2 2-by-6-inch boards, 12 feet long
Saw
Screws
Screwdriver
2 2-by-2-inch boards, 8 feet long
Plywood sheet
2 sheets of 34-by-90-inch Styrofoam insulation
34-by-90-inch sheet of 12 gauge copper
6 7-foot copper pipes, ¾-inch wide
10 ¾-inch copper T-junctions
Work gloves
Eye goggles
Cleaning rags
Can of soldering flux
50-50 solder
MAPP or propane torch
4 ¾-inch copper L-bends
12 ¾-inch male adapters
Drill
2 10-foot plastic tubes
Plumbing caulk
Acrylic or glass sheet sized to fit on top of a 90-by-34-inch box
Epoxy
Black paint

Instructions

- 1
  Cut a 90-inch and a 34-inch board from each 2-by-6 using the saw. Screw these boards together with screws and a screwdriver to form a rectangular frame.
- 2
  Cut out a 90-by-34-inch section of the plywood with the saw. Screw it to one side of the frame, so that you now have a box.
- 3
  Lay the Styrofoam insulation on the bottom of the box. Lay the copper sheet down on top of it. The copper sheet will collect and hold the heat.
- 4
  Clean the ends of 4 of the copper pipes, inside and out. Clean the ends of 8 of the T-junctions, inside and out. Put on the goggles and work gloves. Apply flux to one end of one of the pipes and to one of the T-junctions and fit them together. Heat them with the torch.
- 5
  Touch the solder to the joint once the flux begins to bubble. Remove the torch. Work solder into the joint until the joint is filled all the way around.
- 6
  Solder another T-junction to the other end of the pipe. Solder T-junctions to both ends of all four pipes that you cleaned.
- 7
  Attach one L-bend to each end of the two remaining pipes and solder in place. Use the same method as for the T-junctions.
- 8
  Connect one of the male adapters to either free end of the T-junction on the end of any of the copper pipes using the solder. Solder the other end of this adapter to another T-junction. Point this T-junction in the opposite direction of the first one.
- 9
  Solder another adapter to the opposite end of this new T-junction. To the opposite end of that, solder one of the junctions attached to one of the other pipes. You now have a U-shape of copper pipes, with a T-junction at the bottom. Attach another T-junction to the other ends of these two pipes in the same manner, to make a rectangular shape.
- 10
  Attach male adapters to the remaining free ends of each T-junction on the rectangle and solder them in place. Solder the T-junctions connected to the remaining four pipes with T-junctions.
- 11
  Solder adapters to the free T-junction ends. Solder the L-bends to these. You now have six copper bars connected by manifolds of fittings.
- 12
  Drill a ¾-inch hole in each short end of the box. Insert the ends of the plastic tubes through these holes. Lay the manifold and pipes into the box.
- 13
  Fit the plastic pipes into the open T-junctions in the middle of the manifolds. Seal them with plumbing caulk.
- 14
  Attach the free end of one of the tubes to the fitting on top of the water heater. Fit the free end into the fitting at the bottom of the water heater.
- 15
  Epoxy the acrylic or glass sheet to the top of the box. Paint the exterior of the box black to help it absorb more heat.

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