Make a Solar Hot Tub in One Day for $300

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In Hot Tubs and Motorcycles, I promised to show you how to make your own hot tub. If you begin tomorrow, you can be soaking in fresh, 103? water by evening. In almost every way, my new sun-powered tub is superior to the old redwood tubs of the 70s. Here is what you do:

Go shopping for a metal livestock water trough: On the Internet, I discovered that water troughs come in slightly different sizes so they can fit inside each other for shipping – like Russian Babushka dolls.

To my surprise and delight, our local “Hacienda Hay and Feed” farm supply had a yard full of metal water troughs. My brother made a livestock tank hot tub long ago and suggested that a long skinny tub was a lot better than a big, round one. It took less water and would heat up much faster. Since this would be just for Carol and me, I picked the biggest oval of the stack, which turned out to be over 6 feet long and about 2 feet by 2 feet on the inside. It is rated at holding 169 gallons. $200 later it was in my trailer, heading home.

Next was a visit to the local building supply store where I bought 34, 8″ cement blocks. At $75, I figured that these would be the cheapest way to support us and not catch fire.

Carol watched all this from her kitchen window.

I filled it up about 2/3, leaving room for the water to rise when we got in so If it overflowed it would not put its fire out. That figures to be about 110 gallons. 

The actual firebox is a 55-gallon steel drum, cut off at the first rib with a saber saw, making it 12″ high. This left 4″ for the smoke to exit. I also cut ten, 1″ holes around the bottom to let air in for combustion.

This works perfectly. The firebox heats the center quickly… you can see little bubbles forming directly over it. Where we climb in and sit has blocks under it and is not blazing hot. I put an eye-bolt on each side of the firebox to which I attached a metal chain for pulling it in and out.  

Son, Zak was too young to remember our previous wood fired hot tub, but he likes this one.

Here is what we have learned:

It takes about 30 minutes to fill the tub with water to the second ridge. This is enough water and with two people, it does not overflow.

It takes about 3 hours to heat that much water to the ideal temp, which is considered to be 103? F.

All there is left to do is get in.


If there is smoke coming from the fire, and no wind to blow it away, it can get in your eyes and nose and be uncomfortable. It is best to wait until the fire is mostly glowing embers with no smoke. Then get in. Or, if you have the self-control to wait, heat your tub to beyond 103?, drag the smoking firebox out of the way and then get into the water. It will cool gradually. After 30 minutes or so, you usually want to get out, anyway.

Other than dealing with smoke, I don’t like the fact that the metal sides let the cold in… or the heat out faster than I am used to with wood and plastic.  

But consider the costs of a manufactured “Spa” (they call them spas today): $3,000-$4,000 will buy you a basic modern unit that is ready all the time with hot, filtered and chemical-ed water.

For a $300 total investment, a few sticks of firewood created by the sun (free, discarded Oak pallets burn well) and no other cost, you can soak in your hot tub any time you want – as long as you plan ahead, that is.

More ideas:

I could buy some more cement blocks and arrange a chimney to carry the smoke away. 

I could cut a piece of 1″ thick white packing foam to seal the top to keep out dirt and use the water again. But it is easier to simply drain the tub onto the yard and garden. There are no chemicals in this kind of hot tub water. We irrigate anyway.

Non-Californian living: 

If I still lived in the Midwest, where winters can be very cold, I would probably not use this kind of tub. I would build a permanent tub in the middle of the floor of the house, keeping it hot in the winter with a floor mounted gas flame. No, this would not be sun powered. But it would not take any more energy because all the heat would escape into your house anyway. Best of all, it would eliminate electrical shocks.

In summary:

People try to sell us devices that promise to offer a better lifestyle. After all, in a world of cheap and abundant energy, you can do anything, any time you want. Right? But more often than not, these things complicate our lives. Consider the costs: The equipment, the energy, the maintenance, the filters and the chemicals. My personal experience is that we don’t use a tub every day (in California, anyway) so why pay for keeping it hot and operating all the time? Worse, when it does not work, it is too complicated for us to fix. We must call in a repairman who will probably need expensive parts.

You can build this hot tub yourself! You can maintain it yourself. You can fix it yourself. It will never cost you another penny to operate.

This is just another way to living better… on less energy.

By the way: Only the Ducky thermometer was made in China. Everything else is American. Nice, huh?