Chofu Wood-Fired Water Heater for Hot Tubs

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. And 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.  

Installation
The Chofu will connect to any tub using accessories provided (see connection kit): flexible neoprene tubes, stainless steel pipes, and thru-wall tub ports. (Thickness of the tub wall must be specified to determine the length of thru-wall ports.)
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 recommended)

Operation
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.

Features
• 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

Specifications
• 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.

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.

Heating Schedule
55ºF to 105ºF

Gallons

Time

100

1 1/2 hours

200

2 1/2 hours

300

3 1/2 hours

400

4 1/2 hours