Repair Our Home

Are you dreaming about a long soak in your own hot tub under the stars – maybe with some friends to share it with?

Buying and installing a conventional hot tub will cost you upwards of 4,000 dollars.  After that there will be the constant heating costs. 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.  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!

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 box

• Stand-alone tub

• Filter

• Pump (option, site-dependent)

• Various CPVC plumbing parts

• 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 ½ inch plywood will do for the bottom of the box, with edges from 6 x 2 lumber or whatever comes to hand, and then line it with insulating foam sheet.

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. 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.  

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.  Otherwise a suitable pump of about 120 to 150 GPH rating will need to be fitted in the outlet pipe run.

Short pipe runs with no sharp bends are best.  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.

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 instance.

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.

How long will it take for the water to heat up in the solar hot tub?  Depending on where you live it could take as much as two days to reach a comfortable 110 degrees the first time. Then you will need to keep the water temperature down rather than up!

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 seek out some good professional advice – it really will be a good investment.

 

 

 

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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