Buying a hot tub will set you back at least 3,000 dollars and probably a lot more. Then come the heating bills. But you can build a solar hot tub for under 400 dollars, with no heating costs at all. Nothing!
A diy hot tub is very straightforward. 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. Included should be a full list of materials needed, clear step-by-step instructions and diagrams, plumbing schematics and setting-up details.
The basic components of a solar hot tub are:
- Solar collector box
- Stock tub
- Inline filter
- Pump (optional, depending on the site)
- CPVC pipes, connectors, elbows, etc.
- Safety, inlet and outlet valves
A sheet of corrugated tin laid in a shallow wooden box is the basis of the solar collector. Make the box bottom from a sheet of ½ inch plywood, with edges made from 6 x 2 planks or similar, and finished with an insulating foam sheet as a liner.
CPVC pipes (3/4 inch will do) are laid and fastened along the corrugations and connected in series causing water to enter at the lowest point of the solar collector and leave from the highest. Use CPVC for the plumbing, rather than PVC, because of its better heat tolerance. Use flat black paint for the pipes and box interior, and glaze the top with a ¼ inch polycarbonate sheet.
Use a stand-alone tub of between 150 and 500 gallons, depending on how many will be in it.
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. Finally you should fit inlet and outlet flow control valves as well as a safety valve to relieve excess pressure in the system.
Test the hot tub system for leaks, then fit insulation everywhere – external pipes, sides of the tub and the tub cover (very important, to prevent heat loss at night).
Because the tub is designed to stand alone, any surrounding structure that you decide to add will be purely for convenient access and aesthetics, such as covering up the plumbing.
The positioning of the solar collector is 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.
Will heating the water in the solar hot tub take a long time? 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. Determine the size of tub you want, and where you want to build it. Then invest in some good professional advice – you will not regret it.