Constructing a Wood Fired Hot Tub

What You'll Need
Bulk fluid container
Hacksaw or angle grinder with metal cutting and grinding discs
Metal file
Arc welder and accompanying safety gear
Steel wires
Heating gun
Old Radiator (drained and cleaned)

Is there anything more relaxing than sitting in a wood fired hot tub? If you want to enjoy this on a cold winter evening, you can build your own wood fired hot tub with some woodworking and some metalworking skills.

Step 1—Prepare a Level Base

Plan where you're going to place your hot tub. Once it’s full it will be quite heavy, so plan ahead with a reinforced base. If installing on the ground, you can use sand to create a level base for it to sit on.

Step 2—Buy or Build a Tank

You can build your own hot tub from anything large enough to hold you and tolerate hot water. You can make a wooden hot tub from an old whiskey barrel lined with a pond liner cut to size. You can purchase a hot tub kit. You can even make one from cinder blocks, well mortared, lined with plastic.

One of the easiest ways to get a tank is to buy a metal or plastic bulk liquid tank or stock tank. You can find stock tanks at a local feed store.

Step 3—Preparing a Bulk Liquid Tank

Bulk liquid tanks often have a plastic tank inside a metal cage. If you choose this option, here’s how to prepare it.

  1. Unbolt the crossbars holding the plastic tank in the cage, then remove the tank.
  2. Shear off the top of the cage using a hack saw or grinder.
  3. Shorten the cage to a comfortable height.
  4. Smooth the steel edges using the grinder or a file.
  5. Replace the top ring of the cage (make sure all edges are smooth).
  6.  Put the tank back in the cage.
  7. Draw a horizontal line with a marker just below curve at the top of the tank. Use the cage's lip as a reference when you're drawing the line.
  8. Cut off the top of the tank at your marked line with a hand or hacksaw.
  9. Slice deep slots into each corner of the tank, stopping approximately 1/2 inch above the top of the cage.
  10. Heat the top portion of the plastic with a heat gun, then bend the plastic flaps over the rim of the cage.
  11. Clamp the flaps in place until they've cooled.

Step 4—Prepare Your Heat Source

Heat the tub's water with a commercial snorkel stove or create your own heat source. A snorkel stove is wood burning stove that has a stove pipe or "snorkel" for directing smoke. The snorkel stove sits directly inside the hot tub. You can create a snorkel stove yourself using a heavy metal container that can withstand fire burning directly inside of it.

To create a heat source that is outside of the tub, use an empty, clean radiator placed directly below the bottom of the hot tub. Install piping attaching the bottom of the tub with the bottom of the radiator. Also, install piping from the top of the radiator to halfway up the tub. You will then create a fire under the radiator to make a thermosyphon. The reaction from this process will draw the cold water from the bottom of the tub, heat it, and then return it hot to the top of the tub.

If you choose too create a thermosyphon system, be sure to not sit near the entry point for hot water, as it can burn you. If that does not work for you, the problem can be alleviated by installing a water pump that will return the hot water to the bottom of the tub, however this method will take longer to heat the water.

With either method of heating, it generally takes one to two wheelbarrows of wood to bring the tub to a suitable temperature, depending on the size of your tub.