Want To Build A Solar Hot Tub?
Dreaming of a long soak in a hot tub in your backyard under a starry sky – maybe with some friends to share it with?
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. Then you have to face the heating bills. But a solar hot tub can be made for about 400 dollars, and the heating bills will be zero. Free!
It is very easy to build a solar hot tub. You will have a great centerpiece for your backyard, and it will work in any climate. These systems get so hot that you will need a safety valve to prevent steam building up!
Start with a good set of diy plans. You will need full schematics, clear building diagrams, comprehensive lists of materials and professional advice.
These are the main parts of a solar hot tub:
- Solar collector panel
- Stand-alone tub
- Filter
- Pump (option, site-dependent)
- CPVC pipes, connectors, elbows, etc.
- Pressure relief and control valves
A simple solar collector starts with a sheet of corrugated tin laid in an open wooden box. Make the box bottom from a sheet of ½ inch plywood, with edges made from 6 x 2 planks or similar, and then line it with insulating foam sheet.
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 causing water to enter at the lowest point of the solar collector and leave from the highest. CPVC pipe is best, incidentally, because it has better heat tolerance then PVC. Use flat black paint for the pipes and box interior, and glaze the top with a ¼ inch polycarbonate sheet.
You can try out various stand-alone tubs at your local hardware store and choose a suitable size, usually between 150 and 500 gallons depending on the number of people to use it at one time.
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. If unable to do this you will have to fit a suitable pump (150 GPH should do) close to the tub outlet.
Try to arrange the shortest possible pipe runs and to avoid 90 degree bends. Fitting an inline filter close to the tub water outlet will avoid the task of having to clean out the tub from time to time. Finally you should fit inlet and outlet flow control valves as well as a safety valve to relieve excess pressure in the system.
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).
Any structure you decide to build around the tub will be for aesthetic or practical reasons such as access, since the tub is designed to hold its contents without external support.
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 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 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. Know what size of tub you want and where you want to site it. Then seek out some good professional advice – it really will be a good investment.