Do you dream of a hot tub in your backyard, luxuriating under the stars after a hard day’s work – or perhaps a tub party with champagne and lots of good friends?

Buying and installing a conventional hot tub will cost you upwards of 4,000 dollars.  Then you have to face the heating bills. But you can build a solar hot tub for under 400 dollars, with no heating costs at all.  Zilch!

Making a solar powered hot tub is simple.  You will get a great addition to your garden and you will be able to enjoy it in all weathers.  The water will actually get so hot that you will need to fit a pressure relief valve for safety!

Start with a good set of diy plans.  These should include clear step-by-step instructions, a materials list, schematics and diagrams to show you exactly how to build the solar hot tub.

Basic parts of a solar hot tub are:

• Solar collector panel

• Stand-alone tub

• Filter

• Pump (option, site-dependent)

• Various CPVC plumbing parts

• Pressure relief and control valves

A sheet of corrugated tin laid in a shallow wooden box is the basis of the solar collector.  A sheet of ½ inch plywood will do for the bottom of the box, with edges from 6 x 2 lumber or whatever comes to hand, and finished with an insulating foam sheet as a liner.

The water is heated in a series of ¾ inch CPVC pipes, laid and glued along each groove of the corrugated sheet in a serpentine pattern allowing cold water to enter the solar collector at the bottom and exit at the top. CPVC pipe is best, incidentally, because it has better heat tolerance then PVC. The whole inside of the box and the pipes are painted flat black, and a sheet of ¼ inch (or thereabouts) polycarbonate glazing is attached to the top of the box to close it.

The tub can be any suitable stand-alone stock tank, from 150 gallons capacity (for 1 or 2 people) to 500 gallons or more.

If the solar collector can be mounted one or two feet below the tub (perhaps by having the tub on a slight mound), it is possible to circulate the water through the heating system by thermosyphon action.  Otherwise a suitable pump of about 120 to 150 GPH rating will need to be fitted in the outlet pipe run.

Pipe runs should be as short as possible, and avoid sharp bends.  Fit an inline filter at the tub outlet to avoid the chore of regular water replacement. You will also need control valves at tub inlet and outlet, and a pressure relief valve for safety.

Once you have tested the solar hot tub for leaks insulate as much as possible – any exposed pipes, the external walls of the tub, and the tub cover (essential to lower nighttime heat loss).

The tub will not need any external support so you will be free to build any structure around it you want, to hide the plumbing or provide an access platform, for example.

The positioning of the solar collector is important.  In northern latitudes place it facing due south, or within 10 degrees of it, and sloping at between 15 and 30 degrees from the horizontal. It should also be slightly tilted along its length to allow better water flow.

What time can you expect to take for heating the solar hot tub water?  It might take as long as two days to establish a comfortable 110 degrees first time around. After that your main problem will be keeping the temperature down!

Please keep in mind the absolute need to plan properly before starting to build your solar hot tub.  Decide on the size of tub and where to put it.  Then the best, and safest, bet is to get some good professional advice.