Wood hot tubs are the humble beginnings of the modern spa. The first round wood hot tubs of the 60’s were converted from discarded wine vats from California vineyards. Some wood spas are still sold and in use today, but largely have been replaced by energy efficient portable spas.
Wondering what the difference is between a hot tub and spa? All hot tubs hold hot water, but spas are made of more durable materials like acrylic or resin. They have many more features like advanced filtration, numerous jets, and sanitation. Spas are definitely hot tubs, but wood hot tubs are not usually referred to as spas.
Wooden tubs, often made of redwood or cedar, are constructed in the same tradition as barrel-making, called cooperage. Slotted vertical boards, or staves, are beveled slightly to create a tight fit.
Floorboards are connected together using small dowels, called a pin and hole joint. The slots in the bottom of the staves, called croze, hold the floorboards without nails or glue. Several adjustable metal bands on the exterior are tightened to secure the staves in place.
Wood-fired submersible fireboxes heated early wine-vat tubs, homemade from scrap metal and a little ingenuity. Still made today, these underwater units place the occupants right next to the furnace, protected by a small wooden fence.
Now, exterior stoves are available with a chamber that flows hot water into the tub and cold water out. This is similar to the way ocean currents move water.
Far from the always ready spas of today, these heaters require much work before getting in the tub to relax. Wood must be purchased or cut and split, and a fire must be started for each soak well in advance. In addition to the extra labor, any breeze will blow soot and ash from the furnace into the water.
Wood burning systems do not have temperature regulation. The temperature needs to be checked frequently with a floating thermometer, and the fire dampened to avoid overheating. If the fire goes out, it must be restarted mid-soak to maintain the temperature.
Limited Modern Amenities
To compete with modern, feature rich spas, some builders have added simple heater and filtration systems as upgrades. While these upgrades do address some sanitary and convenience issues, other issues with this design exist.
Not to mention, the original aesthetic charm of a wooden tub is lost with the addition of modern equipment.
With no enclosed cabinet on typical wood tubs, plumbing and equipment is exposed to cold outside air. This inefficient design allows the water in the pipes to cool, wasting energy.
When the pump is re-activated, cold water exits the pipes through the jets, right in the middle of your back! Exterior pipes can also freeze and crack in cold weather without insulation or a warm cabinet to protect them.
Dwindling Lumber Supply
Wood hot tubs require a large amount of lumber from slow-growing, old-growth trees, a precious and diminishing resource. Only heartwood, or the center cut of a tree, is used. Inferior cuts of wood, or those with knots, can leak or split.
Overharvesting of old-growth trees has limited the supply of quality timber available. Due to Federal and State laws, large-scale commercial harvesting of redwood is no longer allowed. This means redwood is not available on most new wood hot tubs, since only young, soft lumber is available.
Western red cedar is most commonly used in modern wood hot tubs. Exotic species like teak are still available, but the cost is much greater.
Most wood hot tubs are shipped as kits, and must be assembled by the consumer. Without experience, poor assembly can lead to serious long-term leaks.
Wood tub manufacturers and dealers often praise a short assembly time of 1-2 hours. Not only is this time represented only for seasoned installers, plumbing is not included in the time frame.
Including a gas or electric heater and filtration requires drilling holes into the finished tub to install jets and plumbing. Those purchasing new wood tubs can expect a large project with many hours of labor and added expense.
Wood tubs require draining and refilling often, and may not be an option in high drought or water restricted areas. Wood-fired units lack filtration altogether, and should be emptied after each use to discourage contamination.
Gas or electric heated tubs with filtration can last slightly longer between fills. Still, they must be drained much more often than their modern counterparts.
Cedar and redwood have naturally-occurring compounds that leach into the water, contributing to poor water quality. Certain toxins present in the wood promote decay resistance, but may be irritating to the skin or respiratory system. Tannins turn water brown and murky, especially with newer tubs.
The porous surface of wood is the perfect breeding ground for bacteria and other contaminants. Even with careful cleaning and sanitizing, wooden tubs are not the gold standard for hot tub cleanliness. As a result, many local health codes prohibit wood hot tubs for public or commercial use.
Standard chlorine and bromine treatments used in portable spas can be detrimental to a wooden tub. Lignin, an organic polymer that aids in the rigidity and decay resistance of wood, is stripped out by these sanitizers. A white coating forms on the inside of the tub, and the wood is weakened permanently.
Gentle mineral sanitizers utilizing metal ions are a much better option in wood hot tubs. The American pioneers used copper pennies to keep drinking water fresh in wooden barrels while crossing the plains. Similarly, Cleanwater Blue uses copper ions to destroy bacteria and algae, without damage to wood structure.
Leaks & Insect Damage
Wood hot tubs are not only difficult to keep clean, but can have serious leaks from the first fill. After assembly and each time the tub is allowed to dry, the tub will leak until the wood swells. For indoor applications, this may damage flooring or underlayment with excess water runoff.
Outside elements can cause cracking, warping, and decay of the wood. During winter, the damp wood freezes and expands, splitting the wood. Wooden tubs are the perfect source of food and water for termites and carpenter ants. These destructive pests can significantly damage the tubs structural integrity.
Empty wood hot tubs dry out quickly and develop even more leaks. When the tub is filled, the wood absorbs with water, swelling to fill each crack. This process is not perfect, and during the "breaking-in" period of a new wood tub, leaks occur readily. The cure is often stuffing damp sawdust into fissures or pouring large amounts directly into the water.
Wood hot tubs absorb water to seal gaps and create a mostly water tight seal. This saturation effectively eliminates any natural insulating value of the wood itself, reducing energy efficiency drastically.
A portion of the heat lost through evaporation can be reclaimed by investing in an insulating spa cover.
Portable spa manufacturers have made huge technological advances in heat retention, and wooden tubs just can’t keep up. Modern spas are low maintenance, easy to install and engineered to save money on heating costs from the ground up.