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.
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:
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:
* 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.
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.
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.