Chofu Wood-Fired Water Heater


The Chofu is a precision-built, high-efficiency water heater designed specifically for soaking tubs. It circulates water using the principal of “thermosiphon” – the pumping action created by rising hot water – eliminating the need for a circulating pump or electricity. This allows a soaking tub to be used in a variety of settings including remote locations.

The Chofu enables you to have a basic, low- cost soaking tub by retrofitting an existing hot tub or by using a stock tank, wood tub, bathtub, etc.

To order the Chofu Heater, click here.

Engineered Design

Every detail of the Chofu Heater has been engineered for maximum efficiency, utilizing a sophisticated heat exchange design. The stainless steel body surrounding the firebox is actually a double-walled water-jacket with a 1-inch space between, making the entire firebox a heat-transferring surface. Additional heat transfer takes place in a water- circulating baffle plate located directly above the fire, which deflects the path of hot gases in a circuitous path.

What Makes the Chofu Unique?

  1. High-Efficiency Heat Transfer
    The Chofu heater achieves extremely high efficiency by using 20-gauge stainless steel in the firebox wall for rapid heat transfer. Only Chofu’s state of the art welding process makes this possible. The genius of the Chofu design comes from the fact that when a fire is burning inside the firebox, water is constantly flowing through the water-jacket and into the tub, replaced by cold water from the bottom of the tub. The stainless steel wall of the firebox/water jacket never gets too hot because it is constantly being cooled. 
  2. Internal Fire Baffle
    Another feature that allows the Chofu to rapidly transfer heat into water and that sets it apart from any other water heater is an internal baffle system. The hollow, water-circulating baffle plate, located inside the firebox, receives direct contact with the flames. It increases the heat transfer surface area and also routes hot gases in a circuitous path – extending contact to the water-jacket. No other water heater has this design feature.
  3. Reflective Heat Shield
    Located behind the heavy steel front is a polished stainless steel heat shield that reflects heat back into the firebox. It’s backed with refractory insulation to prevent heat loss.
  4. Clean Emissions
    The smoke outlet on the Chofu features a vented collar that provides secondary combustion of unburned gases for reducing smoke emissions and chimney sparks.


• Premium grade (308) stainless steel stove body and firebox
• Heavy steel stove front
• Cast iron door with adjustable draft
Durable stainless steel grate
• Tub connections provided (see photo)
• Generous size firebox, 18″L x 14″W x 10″H
• Vented smoke-outlet for secondary combustion
• 3/4-inch drain for freeze protection
• Ash drawer for easy removal of ashes
• Long-handled ash rake provided

• Dimensions: 23″ L x 16″ W x 18″ H
• Weight: 52-lbs.
• Stove body: 20-gauge grade 308 stainless steel
• Stove front: 1/8-in. steel
• Firebox door: cast iron
• Stove grate: stainless steel

Firebox dimensions: 18″ L x 14″ W x 10″ H
• Heat exchange surface area: 9 sq. ft.
• Smoke outlet: 4 in.
• Circulating pipes: 1 3/4-in. outside diameter
• Drain: 3/4-in.

Heat Output: 47,000 BTUs



The Chofu will connect to any tub using accessories provided (neoprene tubes, stainless steel pipes, and wire clamps), and thru-wall ports of your choice. (Thickness of the tub wall must be specified to determine the length of thru-wall ports.)
Installation requires four basic steps:
(1) Prepare a non-combustible foundation (cement or tile) next to the soaking tub to receive the Chofu heater.
(2) Cut two holes in the side of the tub wall for thru-wall ports.
(3) Install connecting pipes from heater to the tub.
(4) Install the stove pipe (8 feet recommended).


The Chofu operates like a conventional wood stove, achieving the fastest heating rate from burning dry hardwoods. It uses 17-inch wood, with the most efficient heating coming from using 17-in. x 11/2-in. x 11/2-in. wood, loaded at 30-40-min. intervals.

Temperature Control

The heating rate is controlled by the amount of air let into the firebox through the adjustable draft in the door – wide open for fast heating, and closed down once water is hot.

Heating Rate Information

Although the heating rate is variable depending on dryness of wood, frequency of loading, etc., the average heat output of the Chofu is 47,000 BTUs. A 200-gallon tub can be heated at approximately 20ºF per hour.

Heating Schedule

55ºF to 105ºF




1-1/2 hours


2-1/2 hours


3-1/2 hours


4-1/2 hours

Freeze Protection

The Chofu can be used in the coldest climates. It can be easily protected during freezing temperatures by draining the water-jacket after the fire is out. These simple steps are required:

  1. Insert freeze plugs into the thru-wall ports from inside the tub.
  2. Remove the drain plug from back of Chofu to drain the water-jacket.
  3. Reverse procedure when tub is used again.

(also see Freeze Protection page)

Chimney Cap (see photo)

Secondary combustion at the smoke outlet of the Chofu eliminates most sparks; however, a chimney cap may be necessary when the heater is used in a fire hazard area or when trees are nearby. 

Note: Using a chimney cap causes a reduction in the velocity of air-flow (draft) through the firebox, resulting in a slower heating rate. To compensate, an additional 2-ft. length of stove pipe can be added to maintain the optimum air-flow. 

Stove Pipe Support Bracket (see photo)

8-ft. of stove pipe is recommended for optimum draft and does not need support; however, when additional pipe is added or a chimney cap is used, the pipe must be supported using a stove pipe support bracket.

Chimney Removal and Storage

When the Chofu heater is not in use or for storage, the stove pipe can be easily removed by lifting the pipe off at the connection between the black enameled collar and the stainless 4-in. pipe adapter. This connection has a very snug fit that does not need to be secured with sheet metal screws, as do all the other connections.