DIY Hot Tub

Want to create a relaxing oasis in your backyard for less than $1,000? We'll show you with this easy DIY hot tub plan.

| June/July 2010

DIY Hot Tub

You can customize your DIY hot tub setup to your wishes. This backyard design includes a wood-fired heater, a handy storage nook and a small shed for stacking wood.


I have lived in the Pacific Northwest with its cool, damp winters for more than 20 years, and I always wanted to build a hot tub. I wasn’t interested in one of the popular jetted tubs because their cost is prohibitive, the pump noise and vibration are bothersome, and the chemicals used to keep the water free of bacteria are a turnoff.

The idea of using a stock-watering tank for a DIY hot tub project has been around for a long time, but all of the ones I’d seen were pretty unattractive. I wanted a setup that was nice-looking, easy to use, and economical. My hot tub dreams came together when I discovered a wood-fired spa stove made in Japan by a company called Chofu and imported by Island Hot Tub Co. Depending on how the soaking area is customized, the setup I’ve designed can cost less than $1,000.

Soaking in a Wood-Fired Hot Tub

Unlike a commercially available tub that only requires you to plug it in and set a timer, you’ll be more involved in the operation of your wood-fired soaking tub. The water is not continually kept hot, so each soak needs to be planned a few hours in advance. I find the involvement is part of the attraction. It creates anticipation that starts with building the fire and culminates with climbing into the steamy, relaxing tub.

The Japanese have long recognized the benefits of soaking in hot water to relieve aches and pains and deal with the daily stresses of life. They typically bathe before soaking to avoid dirtying the water and to maximize the number of times the water can be used before it requires changing. Before each soak, I wash up using hot water dipped directly out of my tub. This keeps the water clean and also acclimates me to the water temperature. Traditionally, the Japanese tend to like their water exceptionally hot, but the Consumer Product Safety Commission recommends the water temperature in a hot tub never exceed 104 degrees Fahrenheit. I keep a hose handy to add cold water if necessary.

Heating and Maintaining the Water

The tub I chose holds 100 gallons if filled to the brim. That much water costs about a buck in our town. Fill the tub 3 to 4 inches from the brim, otherwise the water displaced by your body will be lost when you get in. This setup uses considerably less water than commercially available tubs, thus making it more practical to drain the water frequently, keeping it free of bacteria without using toxic chemicals.

With daily use for two people, we replace the water every four days. When the water needs to be changed, you can simply drain it into a garden area. If you want to keep the water longer or are worried about bacteria growth, add about a quarter cup of 35 percent hydrogen peroxide per 100 gallons (wear gloves and safety goggles during handling). Hydrogen peroxide at this strength is sold as a water clarifier in spa stores. It separates into hydrogen and oxygen in the water, and the oxygen is the active ingredient that kills bacteria.

3/19/2015 7:28:40 AM

Thanks for this post.Someone who just enjoys the the sanctity thermal water can bring, this article is sure to please anyone.

4/9/2014 4:43:05 AM

Hi Greg! Great article, enjoyed reading it!!! I only really recommend winterization. To the hot tub, you may add polyurethane insulation. Check it out Glass enforced plastic inner elements of hot tub offer a good opportunity to build exactly such hot tub as you like. Glass enforced plastic inner elements As long as you have the cover on your hot tub, the heat has no where to go and it maintains a nice warm. Internal or outside heaters I hope that's useful :) Benny

12/15/2010 5:00:03 PM

Many who would like something like this live in climates that freeze! How about addressing how to use in that climate?

abbey bend
12/15/2010 10:31:28 AM

A solar heating system is really no different than a wood, electric, gas, or whatever the heat source is, all will work better on hotter days because of the Third law of Thermodynamics. That being said a solar system is easy to build, done properly needs no pump either, and even on hazy days supplies some heating to the water. 100 or so gallons of water are not hard to heat solar. A thermo-siphon does not need to be very tall to work; a small pedestal for the tub, with a lay-down breadbox style heater will work well. Can be made out of a large piece or pieces of Plexiglas or glass, with a black tank or black ABS piping inside a straw bale enclosure. So a solar heating system can be made for under $100.00 without too much trouble. It will be a bit slower but free to run, and will keep the water hot year round. I do like the stirring Oar!

6/18/2010 4:18:17 PM

The issue is that the solar will work better on a hotter day, not a cold day. There is also the issue that draining the solar system, then bleeding the air out when refilling it. If you use a dedicated fluid transfer system, the cost would be an issue as well. Also, this system uses no power, so unless the hot tub is higher than the solar collector, it will need a pump as hot fluid rises.

6/16/2010 11:09:48 AM

why not heat the water with rooftop passive solar and supplement if the water is not hot enough with wood.

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