CHOFU Wood-fired Water Heater
Stainless Steel, Wood Fired
Includes Connecting Fittings For Tank
This Chofu model is a precision built wood-burning water heater designed specifically for hot 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 unique feature opens up a whole new range of possibilities for alternative hot tubs. Now you can have a basic soaking tub without pumps, chemicals, or high maintenance. With the Chofu heater you can retrofit an existing tub or put together a low-cost soaking tub, using a wooden tub or stock tank.
The stove body of the Chofu is made with high quality stainless steel, grade (316), so it can be used outside, without worry. Since the firebox is also made of stainless steel, it will withstand years of service without danger of burning-out. The smoke outlet on the Chofu features a unique vented collar that provides secondary combustion of unburned gases, for reducing smoke emissions and chimney sparks.
The Chofu utilizes a sophisticated heat exchange design for efficient water heating. The stainless steel stove body surrounding the firebox is a double-walled water-jacket with a 1-inch space between, making the entire firebox (except the front) a heat-transferring surface. Additional heat transfer takes place in a water-filled baffle plate that runs horizontally through the firebox. The baffle deflects the path of the fire, so it gives up more heat into the water jacket before going up the chimney.
The Chofu hot tub heater will connect to any tub using accessories provided (neoprene tubes, stainless steel pipes, and wire clamps), and thru-wall ports of your choice. Through-wall tub ports must be ordered separately. (Thickness of the tub wall must be specified to determine the length of thru-wall ports. We will be happy to help you make the correct selection.)
Installation requires these four basic steps:
(1) Preparing a brick or cement foundation next to the hot tub to receive the Chofu heater.
(2) Cutting 1 7/8-inch holes in the side of the tub wall for thru-wall ports.
(3) Installing pipes to connect heater and tub.
(4) Installing the stove pipe (8 feet strongly recommended)
Manufacturer recommends that users in high fire danger areas install the Stainless Cap. Using the cap requires the brace kit and five sections of pipe for proper draft. In low fire danger areas the cap and brace kit are not needed, and only four sections of pipe are required for proper draft.
The Chofu operates like a conventional wood stove, achieving its fastest heating rate from dry hardwoods. It uses 17-inch wood with an 18-inch x 14-inch x 14-inch firebox. The most efficient heating comes from using 17-inch x 1 1/2-inch x 1 1/2-inch wood, loaded at 45 min. intervals.
The Chofu has a high and low speed draft control to regulate the heating rate. It operates with the draft wide open for fast heating, and closed down to maintain temperature once the water is hot.
• High grade stainless steel stove body
• 1/8-inch steel stove front
• Heavy cast iron door and grates
• Hot Tub Connection kit (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.
• An ash drawer for easy removal of ashes.
• A long handled ash rake
• Dimensions: 16″ wide x 23″ long x 18″ high
• Weight: 59-lbs.
• Stove body: Grade 316 stainless steel, inner wall 20-gauge, outer wall 22-gauge
• Stove Front: 1/8-inch steel
• Firebox door and grates: cast iron
• Firebox dimensions: 18″L x 14″W x 10″H
• Heat exchange surface area: 9 sq. ft.
• Smoke outlet: 4 5/8-inch (reduced to 4-inch)
• Circulating pipes: 1 3/4-inch O.D.
• Drain: 3/4-inch I.D.
One Year Warranty
Not for pressurized water, 10 psi maximum water jacket. 4″ x 2′ sections of Stainless steel stove pipe and a finishing cap are also available. A minimum of 8′ of the 4″ stove pipe is required to create sufficient draw and firebox heating. The cap will make the pipe stack a bit top heavy and therefore requires some stack support. Ideally you would utilize 5 sections of pipe with the cap for proper draw but 4 sections will work. The cap is a very good idea in any area where a fire danger may exist.
55ºF to 105ºF
|100||1 ½ hours|
|200||2 ½ hours|
|300||3 ½ hours|
|400||4 ½ hours|
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 CHS is 32,000 BTU’s. A 200-gallon tub can be heated at approx. 20ºF per hour.
Note: The heat output of the Chofu increases after an initial 45-min. warm-up period that heats the stove body and establishes a bed of coals.