Wood-fired spa heaters offer an alternative to traditional electric or gas heaters, providing a unique and often off-grid heating solution for hot tubs and pools. This article delves into the world of wood-fired spa heaters, examining their features, benefits, drawbacks, and various design considerations.
Understanding Wood Fired Hot Tubs
A wood-fired hot tub utilizes a wood-burning stove to heat the water. These stoves can be either submerged in the tub or located externally. Submerged stoves are considered more efficient as they directly heat the water, while external stoves use a thermosiphoning process where cooler water is drawn into the stove, heated, and then circulated back into the tub.
Key Components
- Wood Burning Stove: The heart of the system, responsible for generating heat through wood combustion.
- Chimney: Vents smoke away from the tub.
- Heat Guard: Protects users from burns.
- Tub: Constructed from various materials like wood, aluminum, or plastic.
- Circulation Pipes/Hoses: (For external stoves) Facilitate water flow between the stove and the tub.
Benefits of Wood Fired Spa Heaters
- Off-Grid Capability: Wood-fired heaters can operate independently of electricity, making them ideal for remote locations.
- Faster Heating (Potentially): Some users report faster heating times compared to electric heaters, especially from a mild temperature.
- Lower Running Costs: Wood can be a cheaper fuel source than electricity or propane, especially if you have access to free or low-cost wood.
- Unique Experience: Many enjoy the ambiance of a wood-burning fire and the natural, chemical-free water.
- Contrast Bath Therapy: Pairing a wood-fired hot tub with a cold plunge pool can offer health benefits through alternating hot and cold exposure.
Drawbacks and Considerations
- Time Investment: Heating a wood-fired tub requires time for building and maintaining the fire.
- Temperature Control: Maintaining a consistent temperature can be challenging without a thermostat. Overheating is a potential risk.
- Water Sanitation: Without proper sanitation, the water can quickly become dirty and unusable.
- Maintenance: Emptying, cleaning, and refilling the tub can be time-consuming.
- Localized Heating: Uneven heat distribution within the tub can occur, especially near the stove.
- Hassle and Spontaneity: The setup and heating process requires planning and isn't as spontaneous as an electric hot tub.
- Water Replenishment: Managing the water can be difficult, potentially requiring frequent replenishment.
Design and Material Considerations
Stove Design
- Submersible Stoves: Efficient, directly heat the water.
- External Stoves: Offer more space in the tub and eliminate the risk of touching a hot stove.
- DIY Heating Coils: A cost-effective option where a fire is built around a coil, heating the water as it circulates.
Tub Materials
- Cedar: A popular choice due to its durability, decay resistance, and pleasant aroma. Western red cedar is a common and cost-effective option. Alaskan yellow cedar is also a good choice.
- Aluminum: Durable, recyclable, and easy to clean.
- Fiberglass: Often used as a liner for wooden tubs to prevent leaks and simplify maintenance.
User Experiences and Reviews
One user shared their experience with an off-grid wood-fired hot tub, highlighting both pros and cons. The tub heated up relatively quickly (from a mild temperature), reaching 39°C (102°F) in about 50 minutes. However, they noted localized heating, a lack of temperature regulation leading to overheating, and a stale water stench the next day due to the absence of chemicals and filtration. Emptying and refilling the tub also proved to be time-consuming.
Another user recounted building their own cinder block hot tub with a homemade snorkel stove. They found that heating the large volume of water took a considerable amount of time. They also had to address the issue of the stove floating and the need for water circulation to ensure even heating.
Maintaining Your Wood Fired Hot Tub
Water Quality
- Chemical-Free Approach: Requires frequent water changes (every 2-3 uses) and wiping down the tub.
- Chemical Sanitation: Using chlorine, bromine, or saltwater can help maintain water hygiene and prevent bacteria and algae growth. Regular testing and pH balancing are essential.
Wood Selection
- Seasoned Hardwood: Oak, birch, maple, or ash are recommended for efficient heating.
Chimney Maintenance
- Regularly remove the stove pipe for storage when the heater is not in use.
Brands and Products
- AlumiTubs: Known for their aluminum-lined cedar hot tubs with efficient heating systems.
- Forest Cooperage: Specializes in Japanese-inspired wood hot tubs crafted with interlocking wooden staves.
- Backcountry Recreation: Offers high-quality wood hot tubs made with Canadian Western Cedar or Scandinavian thermowood.
- Snorkel: Inventor of the underwater hot tub stove, offering both tubs and stoves.
- Wild Mountain Tubs: A new venture with different design to most of the traditional tubs on the market but heat up time is generally under an hour.
- Skargards: Good build quality. Takes about 45 mins to fill and about 2.5 hours to heat up to a decent temp.
- Chofu: Precision-built, high-efficiency water heater designed specifically for hot tubs.
DIY Considerations
Building your own wood-fired hot tub is possible. One example detailed building a functional hot tub with a cold plunge for around $2,000.
Enhancements and Modifications
- Flue Damper: Adding a flue damper to the chimney can help control airflow and improve efficiency.
- Air Intake Adjustments: Modifying the air intake to provide more even distribution to the fire.
- Gaskets: Adding gaskets to the doors to reduce smoke stains and heat loss.
- Heat Exchanger Modifications: Channeling heat to travel farther over the pipes to increase efficiency.
- External Heating: Adding an additional heat exchanger for air heating.