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Chofu Wood-Fired Hot Tub Heater
Precision-built in Japan, the Chofu Wood-Fired Hot Tub Heater is an electricity-free wood-burning water heater designed specifically for hot tubs. It circulates water using the principle 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 tub setups and eliminates the expense of a thermostatically-controlled heating system. Now you can have a basic soaking tub without pumps, chemicals, high maintenance, and the excessive energy required to keep a tub hot even when it's not in use. With the Chofu Hot Tub Heater you can retrofit an existing tub or put together a low-cost soaking tub using a wooden tub or stock tank.
The Chofu utilizes a sophisticated heat exchange design for efficient water heating. The grade-316 stainless steel stove body surrounding the firebox is a double-walled water-jacket with a 1" gap, 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 firebox is also made of stainless steel, allowing it to withstand years of service without danger of burning out. The smoke outlet features a unique vented collar that provides secondary combustion of unburned gases for reduced smoke emissions and chimney sparks.* Can be installed outside.
Chofu Wood-Fired Hot Tub Heater Features
- High-grade stainless steel stove body
- ⅛" steel stove front
- Heavy cast iron door and grates
- Includes hot tub connection kit
- Large 18" x 14" x 10" firebox
- Vented smoke outlet for secondary combustion
- ¾" drain for freeze protection
- Ash drawer for easy removal of ashes
- Long-handled ash rake
Installing the Chofu Wood-Fired Hot Tub Heater
The Chofu will connect to any tub using the included hot tub connection accessories (flexible neoprene tubes, stainless steel pipes, and thru-wall tub ports). Installation requires four basic steps:
- Preparing a brick or cement foundation next to the hot tub to receive the Chofu heater
- Cutting 1⅞" holes in the side of the tub wall for through-wall ports
- Installing pipes to connect the Chofu with the hot tub
- Installing the stove pipe (sold separately here in 2' lengths; 8 feet recommended)
Operating the Chofu Wood-Fired Hot Tub Heater
The Chofu operates like a conventional wood stove, achieving its fastest heating rate from dry hardwoods. The most efficient heating comes from using 17" x 1½" x 1½" wood, loaded at 45-minute intervals. It uses 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.
Although the heating rate is variable depending on dryness of wood, frequency of loading, etc., the average heat output of the Chofu is 32,000 BTUs. A 200-gallon tub can be heated at approximate 20°F per hour. The heat output increases after an initial 45-minute warm-up period that heats the stove body and establishes a bed of coals.
To heat a hot tub from 55°F to 105°F, the following amount of time should be expected:
- 100-gallon tub: 1½ hours
- 200-gallon tub: 2½ hours
- 300-gallon tub: 3½ hours
- 400-gallon tub: 4½ hours
* Secondary combustion in the Chofu Wood-Fired Hot Tub Heater eliminates most sparks; however, a chimney cap may be necessary when it is being used in a fire hazard area or when the stove pipe exhausts near trees. While a chimney cap will cause a restriction in the air flow (draft) through the firebox resulting in a slower heating rate, an additional 2-foot length of stove pipe (available separately) may be used to compensate and maintain an optimal draft.
Chofu Wood-Fired Hot Tub Heater Specs
- 16" W x 23" L x 18" H
- Firebox dimensions: 18" L x 14" W x 10" H
- 59 lbs
- Average heat output: 32,000 BTUs (depends on dryness of wood and frequency of loading)
- Made from grade 316 stainless steel (inner wall 20-gauge, outer wall 22-gauge)
- Stove front: ⅛" steel
- Firebox door and grates: cast iron
- Heat exchange surface area: 9 square feet
- Smoke outlet: 4⅝" (reduced to 4")
- Circulating pipes: 1¾" outer diameter
- Drain: ¾" inner diameter
- Manufacturer: Island Hot Tub Company
The Chofu Wood-Fired Hot Tub Heater must be protected from freezing to prevent damage. The included through-wall ports with threaded plugs allow you to keep water in the tub while draining just the heater. To drain the heating unit, plugs must first be inserted into the ports; then remove the threaded drain plug at the rear/bottom of the heater to drain water out of the Chofu. Please note: firing up the Chofu when it is empty of water will quickly damage the heater. The Chofu water jacket must always be filled with water and the tub ports open to allow water to circulate through the water jacket and therefore cool the firebox metal.
Alternative Freeze Protection Methods
- Drain the tub - this will remove about ⅔ of the water from the Chofu water jacket. The remaining water can be drained by removing the drain plug at the rear/bottom of the heater.
- Covering the Chofu - this method can be used instead of placing plugs in the through-wall ports and draining the Chofu. However, it requires that you make an insulated cover that can be placed over the Chofu. The cover can be either a soft insulated (tea cozy) type or a hard-shell wood structure. Covering may provide adequate protection for nighttime temperature drops just a little below freezing, but for long term protection, the enclosure must snug up against the tub to protect the circulating pipes and the heater, and must have an external heat source, such as a light bulb or heat tape. The tape can be wrapped around the bottom stainless circulating tube, causing heat to rise up through the water jacket and into the tub.
When the Chofu heater is not in use (and also to allow it to be covered), the stove pipe may be removed. This can be accomplished by lifting off the pipe at the connection between the black enameled collar and the stainless 4" pipe adapter. This connection has a very snug fit, thus does not need to be secured with sheet metal screws.
This product is shipped directly from the manufacturer or distributor and will arrive separately from any other products ordered. Availability estimates are based on average lead times and can vary due to stock status and location.
Returns & Replacements
Products can be returned for a refund within 30 days of receipt if unused and in original packaging. Returns are paid for by customer unless product is defective or damaged, in which case Real Goods assumes responsibility. Please use Fedex, UPS, or USPS with tracking, for returns.
Returns of solar panels, inverters or other large ticket items will incur a re-stocking fee of up to 20%. Freight shipping is non-refundable.