Archive for May, 2010

Building a Solar Hot Tub Is Easy

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

A conventional hot tub will cost you at least 3,000 dollars to buy, and there will be the fitting costs on top of that. After that there will be the constant heating costs. But you can build a solar hot tub for less than 400 dollars, and the heating bills are zero. Zilch!

Making a solar powered hot tub is simple. The result will be the centerpiece of your garden and will work in all climates. You will need to fit a safety pressure valve to prevent steam build-up – the water will really get that hot!

Begin with a good set of diy plans. Included should be a full list of materials needed, clear step-by-step instructions and diagrams, plumbing schematics and setting-up details.

These are the main parts of a solar hot tub:

Solar collector panel

Stock tub

Inline filter

Pump (option, site-dependent)

Various CPVC plumbing parts

Pressure relief and control valves

The solar collector can be a simple sheet of corrugated tin in a shallow wood box. The box base can be made of ¼ inch or ½ inch ply sheet, with edges made from 6 x 2 planks or similar, and line it with a 1 inch sheet of insulating foam.

A series of ¾ inch CPVC pipes are fixed in each corrugation 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. Paint the inside of the solar collector box and the pipes flat black, and close the top with a sheet of polycarbonate glazing.

Use a stand-alone tub of between 150 and 500 gallons, depending on how many will be in it.

Mounting the solar collector at least one foot lower than the tub will allow thermosyphoning of the water. If this is not possible you will need a pump rated at about 150 GPH fitted at the outlet from the tub.

Short pipe runs with no sharp bends are best. You should fit a filter near the cold water outlet, otherwise you will need to empty and refill the tub regularly, which is a chore. Inlet and outlet valves (to control water flow) and a pressure relief (safety) valve should also be fitted.

Once you have tested the solar hot tub for leaks insulate as much as possible – external pipes, sides of the tub and the tub cover (very important, to prevent heat loss at night).

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 instance.

Proper positioning of the solar collector is very important. In the northern hemisphere it should face due south, or no more than plus or minus 10 degrees from it, and it should slope between 15 and 30 degrees from horizontal. It should also be slightly tilted along its length to promote the upwards flow of water through the collector pipes.

What time can you expect to take for heating the solar hot tub water? It depends on where you live, but it could take up to a couple of days to reach a comfortable temperature of about 110 degrees the first time. Once there, though, you will find your main problem will be cooling the water rather than heating it!

Remember, proper planning is essential before you start to build the 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.