Dreaming of a long soak in a hot tub in your garden under a starry sky – or perhaps a tub party with champagne and lots of good friends?
Buying a hot tub will set you back at least 3,000 dollars and probably a lot more. After that there will be the constant heating costs. But a solar hot tub can be made for about 400 dollars, and the heating bills will be zero. Nothing!
It is very easy to build a solar hot tub. You will have a great centerpiece for your garden, and it will work in any climate. 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. 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 box
- Stock tub
- Filter
- Pump (option, site-dependent)
- CPVC pipes, connectors, elbows, etc.
- Safety, inlet and outlet valves
A simple solar collector starts with a sheet of corrugated tin laid in an open wooden box. A sheet of ˝ inch plywood will do for the bottom of the box, with edges from 6 x 2 lumber or whatever comes to hand, and line it with a 1 inch sheet of insulating foam.
CPVC pipes (3/4 inch will do) are laid and fastened along the corrugations and connected in series so that cold water enters at the lowest point and exits at the highest. 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.
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 this is not possible you will need a pump rated at about 150 GPH fitted at the outlet from the tub.
Try to arrange the shortest possible pipe runs and to avoid 90 degree bends. Fit an inline filter at the tub outlet to avoid the chore of regular water replacement. Inlet and outlet valves (to control water flow) and a pressure relief (safety) valve should also be fitted.
After testing the solar hot tub for leaks fit as much insulation 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 encourage better water flow through it.
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!
It is essential, however, that you plan in thorough detail before starting to build your solar hot tub. Determine the size of tub you want, and where you want to locate it. Then invest in some good professional advice – you will not regret it.
Tags: build your own hot tub, diy hot tub, homemade hot tub, solar hot tub, solar hot tub heater, solar powered hot tub, solar spa heater
