Doug and Erin's wood-fired hot tub
For a while my friend Doug and I had discussed how best to create a simple wood-fired hot tub. Stressful jobs require drastic measures to help maintain one's health and happiness. Doug took action and created a truly wonderful soaking tub.
Conventional acrylic hot tubs work fine but, frankly, I find them a little stupid. They are expensive to purchase and maintain. It's a little offensive how much energy is consumed maintaining hot tubs at regular operating temperature 24 hours a day. Such a waste! Then there are the chemicals. You always see half-working hot tubs on Craigslist. After paying high utility bills for a couple years, those who don't really appreciate their tubs seem desperate to get rid of them. (Note: Huge thanks to all of my friends who have let me soak in their tubs. Don't let my opinions dissuade you from inviting me over. Ha! I appreciate your sacrifice for me and others!)
Wood fired soaking is not perfect but there are fewer on-going expenses and maintenance hassles. I find the aesthetic appeal of a good hot fire an important part of the relaxation and rejuvenation ritual. Fire provides a raw primordial satisfaction. It's comfort food for the soul.
There are a number of options out there.
There are fancy cedar tubs with specially made submersible wood stoves made by Snorkel Hot Tub in Seattle. Sea Otter Wood Works in Haines, Alaska also makes beautiful cedar tubs that are heated various different ways:
There is the trendy hip Dutch Tub:
There is the extremely rudimentary Cowboy Hot Tub.
Doug settled on another option that falls more on the simple/affordable/DIY side of the spectrum and I think he's hit on something that works great!
Here is the tub:
Under the pergola is a 300 gallon Rubbermaid stock tank (aka a cattle watering trough). Not very visible to the right is a Japanese Chofu wood-fired hot tub stove. On the left is a 150 Rubbermaid stock tank for cold water dunking. (The dunk tank has recently been replaced with a vintage cast iron claw foot bathtub.)
Here's a closer look. Looks inviting, no?
The stove for the tub was purchased from Island Hot Tubs, a distribution company for Chofu. (Doug reports having a positive transaction.) Their website is built around promoting this "stock tank" method of hot tubbing. The Island Hot Tub web site doesn't have much in the way of example hot tubs so I figured this post would help illustrate a working model in action.
Here are some details of the stove and the water connection to the stock tank.
The water is heated via convection current. Cold water enters through the lower pipe and exits into the tub from the upper pipe. Putting a hand over the outlet gives a good sense of the impressive heat and rate of flow. The fire box is designed to burn hot and fast and is surrounded by a jacket of water for heating.
Here Doug stokes the fire. It's a fairly small fire box but it puts out a lot of hot water. I've only arrived to enjoy the hot tub. I haven't been around to light the fire and heat the water up all the way from standing outside (cold) temperature. Obviously this takes more planning, effort and commitment than a conventional hot tub. Doug says it takes about three to four hours depending on the outside temperature.
For water sanitizing they follow Island Hot Tub's recommendations of using concentrated hydrogen peroxide. This method is inexpensive and chemically benign since the chemical quickly breaks down to oxygen and water.
The 300 hundred gallon tank seats 4 people comfortably. Five or six is probably possible but it would displace a lot of water and it might be a bit cozy.
Future plans are to add a passive solar booster to shorten the warm-up time.
postscript: Be sure to check out Doug's revised version of his hot tub here.