Introduction: Homesteader Wood Fired Hot Tub

I have always wanted a cedar wood fired hot tub. After checking prices I realized I needed to find a more realistic dream. So I began the research process and found a few people who had done what I wanted to attemp. I combined the best ideas from those and came up with a solid plan. This tub cost under 300 and requires no electricity. All materials were easy found at the home improvement store and farm supply chain.

Step 1: Procure Materials

Gather your materials. You will need a tank around 100 gallons or so. Bigger the tank the harder to heat. I went with a rubbermaid 150 fits 2 people great under 2 hundred dollars. 20 feet of 1/2" copper tube. Diameter and length will effect heat time. The proprr fitting to secure copper line to tank. I used 1/2" compression fittings to 1/2" pipe thread then found fitting made to seal to a tank with matching thread sizes. Then a few rims or similar metal scrap to build a burn chamber.

Step 2: Placement

If the area you want your tub on isn'ta hard level surface make one. I used a pallet the tub fit perfectly on.

Step 3: Making the Thermo-siphon (Chofu) Heater

Your copper tubing should come in a roll, unwind it till it looks thusly and fits in your stove snuggly. For the thermo-siphon to work one end needs to be higher than the other. This will be the hot water out. Be careful it comes out boiling and often shoots out quickly. Yes I burned myself while testing it out. The coil must never be run dry or it will be damaged. It should have a lid so it can be dampened down if it gets out of control or to control smoke while soaking. Due to the popularity of creative stoves here, I decided mine needed character. So I added elephant ears a trunk, eyes and glasses. I set my stove body on a rim, it fit perfectly. Notice the holes in the bottom of the stove, these were there already and will allow air in to allow a good burn. I used a rim for a lid welded up the rim holes, added a hinge, handle and stove pipe. The stove pipe diameter is a little small.

Step 4: Attaching Heater to Tub

Line the leveled stove up to the leveled tub and mark the spot. Drill then carefully cut or hole saw a hole for the gasketed tank fitting. Telfon tape on any non gasketed non compression connections. Many connection styles will work, possibly even a length of hose to a hose barb in place of the compression fitting. My lower piped leaked a bit at first.

Step 5: Inspect and Fill!

After inspecting all connections, checking tub for level-ness, etc. Fill your tub, and wait to fire it up till the coil is filled completely. The tub will not function unless the coil is fully below the water level. I takes me 8 hours or so of burn time to get my tub up to temperature. Also be careful of the 120+ degree water coming out of the coil. It can scald.

Comments

author
livichris (author)2014-09-30

how does the water circulate through the system. is there a pump?

author
cbissett (author)livichris2014-10-13

Hot water just like air rises. Since the coil is a constant rise it slowly circulates the water through the pipe automatically, Though its slow the water coming out is very hot almost boiling so be carefull. I either stir the tub or have added a small pond pump to shoot cold water from the bottom to the very hot top layer. Evens everything out.

author
DavidE342 (author)2017-03-13

How has the copper coil held up being in direct contact with coals and flame? Really want to build one but was curious about that! Thanks for the awesome post!

author
joetribe (author)2014-09-30

Can this be used with gas

author
panne (author)joetribe2016-02-24

gas or propane would work, but most of the heating comes from the coal bed sitting on my coil. it would burn a lot of gas or propane to initially heat, the same it does with wood. the flames don't heat it as much as the coals. large masses aren't quick to heat up or cool down, so heating takes time. slow and steady with smaller fires or heat sources giving yourself ample time works the best. with a few small gas flames under the coil and a bit of tinkering you could probably keep it heated for cheaper than using wood.

author
cbissett (author)joetribe2014-10-13

Absolutely, anything to heat up the coil. I'm thinking of trying that myself, tending a fire for hours is getting boring. Ive also been cheating with a propane stove boiling water to speed up the process.

author
visualsenses (author)2015-12-07

Always the fire and wood idea in Barel etc. We have a big spa bath for two but hot tub heater is broken. Is the pipe rolled around in circle? Would that work if the hot water pipe would run through a 96sq feet green house in BC Canada. Just to keep above freezing?

author
panne (author)visualsenses2016-02-24

you would probably have too much head pressure going through that much tubing. the cold water ahead of the heated water acts like a plug pushing down, causing surges and unsafe pressure inside the tubing that could cause it to burst. for a greenhouse i would attempt something similar, but use a large compost pile for the heat source or rocket mass heater.

author
panne (author)2014-11-14

if you shorten your tubing to about two wraps, add a check valve and cover your tub, it will heat up a lot faster. you should be able to get a temperature rise between 6-12 degrees per hour with the set up you have, possibly more. a large blanket or tarp draped over a beach ball works well as a cover. without a cover, it's a really hard fight to heat it faster than it cools off. when the coil is too long, it flows slower, due to added resistance.

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author
deltafour (author)panne2015-12-14

Where would put the check valve?

author

If you were going to add a check valve, I would install it on the lower side of the tubing, coming from the tub, into the fire box. Flow arrow facing toward the fire.

author
cbissett (author)panne2015-07-02

I have a Styrofoam cover, I bumped up my tube size to 1 inch. It now takes about 3 hours to reach temp. With about 3 pallets worth of wood.

author
seamster (author)2014-09-29

Nice work! Thanks for sharing this.

author
cbissett (author)seamster2014-09-30

No problem, mit was a long lived dream of mine. I did all ky research on here and felt there needed to be a more definitive design with better materials. It worked so well I needed to inform everyone! Thanks for looking.

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Bio: I have been restoring volkswagens for 10 years and doing metal sculpting for far longer. I have sold sculptures internationally as chrisbcritters on etsy. Here ... More »
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