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Self-reliance and sustainability in the 21st century.

Make a Solar Hot Tub in One Day for $300

By Craig Vetter

Tags: solar hot tub, living better on less energy, sun powered hot tub, Craig Vetter,

Solar Hot Tub Soaking 

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:

 Babushka Dolls 

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.

Water Trough Shopping 

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 Vetter Watching 

Carol watched all this from her kitchen window.

Filling Hot Tub 

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.

Hot Tub Firebox 

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.  

Thumbs Up for Solar Hot Tub 

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?

12/9/2013 4:41:18 PM

I went and got me a trough to build this hot tub but I realized that the sealant at bottom corners of the trough may not withstand the heat from fire and eventually melt. Does anyone have this issue? The trough I bought are made by Countryline Tractor Supplies and the color of the sealant is grey.

12/9/2013 4:36:21 PM

I went and got me a trough to build this hot tub but I realized that the sealant at bottom corners of the trough may not withstand the heat from fire and eventually melt. Does anyone have this issue? The trough I bought are made by Countryline Tractor Supplies and the color of the sealant is grey.

elizabeth harrell
10/9/2013 1:12:19 AM

How do u drain the water out.?

elizabeth harrell
10/9/2013 1:02:35 AM

How do u drain the water out.?

toni watt
1/26/2013 11:59:54 PM

I thought it was a solar hot tub?

1/25/2013 12:17:49 AM

I would build a rocket stove to counter the smoke problems.

steve walters
4/13/2012 5:39:31 AM

"permanently".... typo. Sorry.

steve walters
4/13/2012 5:35:33 AM

I have to agree with others questioning if it's really a 'solar' hot tub, but admire your ingenuity. Our version is similar. It consists of an old claw foot bath tub, on blocks, a pit under the center with stone lining it for the wood fire, and nothing else. The tub cost us $25 from a movie I worked on, and it's cast iron, so holds heat pretty well. There are only 4 blocks at a buck each, and the rocks came from around the land. There was a funny email joke going around a few years ago that had the same 'system' in place. It was called the 'redneck hot tub'. I laughed when I saw it, but had the tub sitting around. It works pretty well. A good fire under it will heat it in less than two hours, and if we let the fire go down to a smolder, it will keep the water warm for a long while, even when it's in the thirties up here in the mountains. We bring a pump spritzer out with us to douse the fire if the water gets too hot. A few pieces of sage staged next to the tub warms it quickly when it begins to cool, and smells good as a bonus. It a simple setup. The actual 'solar' hot tub I will be permantly installing will include water heating panels which are pretty easy to construct, and a larger tank to soak in. I'll post updates when it's built.

crimson mavrick
2/15/2012 6:34:19 AM

Hello Craig, Would in be better to store the hot water in a thermally insulated tank? A mechanical heat pump or water hammer could make it hotter and keep it hot while in use. It could also maintain the temperature of the water (keep it warm) so it can be used as the domestic hot water supply. The Japanese culture had a tradition of taking very long hot baths, but last I heard they had to stop due to resource constrains due to keeping the water hot. I see where the confusion is regarding wood being solar power. Usually we like to think of things as solar when the suns energy is directly harvested through solar collection of the radiant energy. That being said, Trees are pretty good solar collectors and the Carbon that makes them was sequestered from the atmosphere. Returning it there for nature to recycle it into more trees is sustainable if it is being done on a scale that does not cause deforestation in the process. On a mechanical (directly solar) harvesting front; while researching vehicle systems I came across some interesting articles about Hydraulic drive trains. There are these things called hydraulic accumulators that can have significant mechanical power storage capabilities. They allow constant power input to be stored in a (battery/capacitor type) way that allows the system to draw out high demand at peak times. Say you had a solar panel constantly turning and electric motor that is pumping hydraulic energy into the accumulator. Now let’s say you want to turn many gallons of water from warm or cold into hot tub temperature. Take the water hammer or Stirling heat pump and power it hydraulically via the energy stored in the accumulator. It will not run it all day but as you stated the tub only has to be hot when in use. Jase_Alex aka CM

craig vetter
1/28/2012 3:18:17 PM

Well, it is great to see some responses. Thank you. Lets begin with wood being from the sun. Wood heated homes are indeed solar powered. I planted the wood we burn in the 80s. The sun - thru evaporation and rain - brought in the water. The sun caused the photosynthesis to make my trees grow. Of course wood is solar energy. Think of it as "compressed sunlight" . As I write, the sun is producing more wood in front of me. Is gas and petroleum solar, meaning it was once some kind of living material? Nobody really knows how gas and petroleum are made. Popular culture thinks it is animal and or vegetable matter compressed over millions of years. Others think it is anaerobically created within the earth by the temp. difference between the hot core and the surface. For me, the "millions of years" concept convinces me that the more direct way and quickest way we can harvest the energy from the sun, the more we will have and the longer it will last. The sun is making more wood for me right now, in my lifetime. Learning how to live within our own budget of energy means not borrowing from the past. It means not importing energy from others. It means not using it faster than it is being generated. Cheap and abundant energy is the basis of Western civilization. Energy does not get cheaper or more abundant than directly from the sun. Lets figure out how to use it. It is what I think about, relaxing in my sun powered hot tub.

j mills
1/25/2012 4:05:23 PM

Solar hot tub REALLY come on thats ridiculus. I guess I heat my house with solar since I have a WOOD STOVE?

anna kessler
1/22/2012 6:03:09 PM

Nice try, but no cigar. Forget the woodburning and all the smoke, etc. Just place a parabolic window next to it that tilts. When the water gets too warm, tilt the mirror or pull a dark window shade down over the topside. Smiles, Annie in KC

carole gunn
1/21/2012 2:24:11 PM

Sounds like a nice plan. Wonder if placing the tub in a sunny location and using old storm windows over the top to heat the water would also work.

dot huth
1/21/2012 1:40:23 AM

We had this same set up when we were kids as our only bathing source; we used a bathtub with a fire under it and cut out a peice of thick plywood that sat on the bottom of the tub which prevented any burning.

robert white
1/21/2012 12:48:46 AM

This reminds me of the galvanized tub my siblings and I bathed in as kids prior to moving into a modernized house when I was about four. I remembered some type of oil burning stove that was used to heat the water. We would sit by it to keep warm waiting for our turn to get into the tub. I fell against the stove once. I don't think I got burned badly but mom sure made a fuss of it.

jose garcia
1/20/2012 9:38:51 PM

OK, maybe calling this "solar" didn't fit the typical use of the word but....We had a hot tub just like this in 2005-2006. It was handed down from a neighbor who made it years before that - so those of you who say rubbish - WRONG! It held up great. We did build a firebox with several sections of stove pipe attached and a cap for smoke/sparks. We also had a slatted wooden platform to sit on - nicer than block or stone. It heated up quickly and felt great at the end of a hard day of construction. We've since graduated to a snorkel tub and passed the "hillbilly hot tub" onto another. Depending on where you live, a managed woodlot for firewood and construction materials is a sustainable part of the homestead. Our woodfired hot tub fits our permaculture site as well as the cob house and the solar elect. and hot water systems.

darnell fugate
1/20/2012 8:31:03 PM

Love this but when we make our hottub we want to use our gas firepit underneath to heat the water. Great for these hot summers here in Georgia and much less expensive than purchasing a spa. If we want to keep the water and reuse we several time we can always the pump we still have from our grandkids vinyl swimming pool and use the same kind of chemicals we used in it. When we get ready to empty it the plants will be thankful too. Will definitely be using one of these this summer, if not for a hot tub then for a small swimming pool... at least it will not spring a leak. :)

keith hallam
1/20/2012 6:08:27 PM


wayne johnson
1/20/2012 4:49:11 PM

I agree, certainly nor solar, and the bottom of that tub will quickly deteriorate from the fire, then rust, then be an expensive piece of scrap.

alice campbell
1/20/2012 3:11:23 PM

Since when is burning wood considered Solar power? Is oil solar because it started out as a plant a million years ago?