Wood-fired hot tubs offer unparalleled rapid water heating time, excellent economic efficiency and increasing levels of comfort with every advance in spa technology. Naturally, wood-fired hot tubs are making more of an appearance in your neighbours’ backyards, no matter how spacious or tiny – so, is it time for you to take the plunge too?
Before making the decision to purchase a wood-fired hot tub, it’s important to consider how they work, what they are made of and how that affects your bathing experience. In this guide, we answer the following questions:
- How does a wood-fired hot tub work?
- How are wood-fired hot tubs designed?
- What are wood-fired hot tubs made of?
How does a wood-fired hot tub work?
A wood-burner stove uses the energy from fire to heat water. As it takes an extremely powerful electric heater to achieve anywhere near the same level of heat produced by a burning furnace, wood-fired heaters are typically the fastest and most economical on the hot tub market at heating water for a toasty spa experience.
Water circulation within the heater
Gravity is the governing principle that causes water to circulate through the heater. Cold water stays at the bottom of the tub and enters the heater through the lower inlet hole. As it warms up, the heated water rises, leaves the heater through the upper outlet hole and returns to the tub. This process keeps the water constantly moving, getting increasingly warmer without any need for a pump.
Remember to stir the water to disperse the warm water equally throughout the tub, otherwise, you will feel the layers of different temperatures.
Water filtration
A water filter is used to trap impurities present in the water. A water filter alone, however, will not eliminate bacteria or algae that can quickly build up in warm water. For this reason, water sanitisers are also required.
Massage systems
Wood-fired hot tubs contain specially designed systems that channel massage currents through nozzles installed in the walls of the hot tub. These currents are driven by pumps that require electricity to function. Hydro currents or air jets are used to create the massage effect in hot tubs.
How are wood-fired hot tubs designed?
All-wood design
All-wooden hot tubs feature a 100% wooden design which offers less costly construction, fully recyclable elements, a natural touch and appealing wood smell and they tend to be designed to enable off-the-grid use.
On the other hand, a drawback of all-wooden hot tubs can be that they typically offer a less comfortable experience while sitting and reclining due to their 90-degree edges and hard surfaces.
Wood-fired hot tubs without a liner also require more effort when cleaning them. Sensitivity to chemicals renders the all-wooden models unsuitable for leaving the water in the tub for long periods of time, so it is necessary to replace the water after 1-2 uses the following day.
The timber planks will “move” in response to atmospheric conditions. A certain level of moisture must be ensured to guarantee that the joints do not leak. If the tub gets too dry, cracks will appear, causing leakage, which will only disappear when the wood is refilled with water and the timber swells naturally. For a hot tub owner, this means extra time and effort.
Wooden exterior and lining
A wood-fired hot tub with wooden exterior and sleek lining provides a comfortable experience as the ergonomic contours of the wood are well-adapted to the human body. In addition, they are exceptionally easy to clean. The water in the hot tub can be sanitised and kept for a longer time instead of replacing it after just 1-2 uses. Many models typically come with spa elements, such as massage systems and LEDs, along with water filters.
Type of heater
The type of heater used may impact the amount of space it occupies, either in the tub itself or in the garden. There are a range of different heaters, including:
- An external heater can yield the most heating power, but it takes up more space in the garden and requires extra caution when moving around it.
- A snorkel/submerged heater takes up no garden space, but it will occupy a substantial part of the tub and be more challenging to clean.
- An integrated heater looks especially pleasing to the eye, as it doesn’t even require an inch of garden space and only uses a minimal amount of tub space.
- An electric heater, offered together with or in place of a wood-fired stove, will take more time to heat the water and therefore increase your electricity bills. However, it is more convenient as you can “set and forget” it as well as keep the water in the tub at the desired temperature with no hands-on effort.
Type of water filter
Not all wood-fired hot tubs use a water filter. Off-the-grid models are intentionally designed without any electric devices, such as a water filter. Models that do use a water filter will usually have either a cartridge filter or a sand filter installed.
Types of water filters include:
- A cartridge filter is easy to operate and maintain and is generally cheaper than a sand filter. However, the cartridges have to be replaced fairly often.
- A skimmer or a hang-on filter uses a coarse filter before passing the water through a cartridge. It works in much the same way as a cartridge filter, except you need to place the filter unit inside the tub, take it out after use, store it in a safe place, then bring it out again for future use.
- A sand filter only needs to have its filtration system replaced once every a few years. Recyclable filter balls can also be used to make this into an environmentally-friendly option.
- A UV lamp is also offered by some brands to help decrease the amount of chemicals used for water disinfection.
Type of massage system
There are three main options when choosing a massage system for your hot tub: hydro currents, air jets or a combination of the two.
- Hydro jets create a stronger, more focused massage. However, it is worth noting that the system requires additional maintenance to prevent biofilm formation in the tubes.
- Air jets provide a gentle full-body massage requiring no maintenance efforts at all.
What are wood-fired hot tubs made of?
As with the technology solutions listed above, the materials used in the manufacturing of wood-fired hot tubs will have a significant effect on your hot tubbing experience, ease of use and maintenance and the durability of your chosen model. Let’s now discuss the most commonly used materials across the industry.
Wood
Aspects like price, durability, weight, colour and ease of maintenance will vary between different types of wood. The most common types of wood used are as follows:
- Thermowood ensures superb resistance to rot and stability in different weather conditions. It only requires treatment to retain its original brown colour, otherwise it can be left untreated.
- Spruce is the most economical type of wood but it requires regular maintenance work.
- Oak is exceedingly strong and durable and has a distinctive look, but is also very expensive.
- Cedar is characterised by its outstanding durability and it offers the best heat insulation properties, but it has a rough texture and is the most expensive.
- Composite cladding is not wood at all, but rather it is made of recycled household plastic waste. This material offers excellent weather resistance and requires little maintenance. We will leave you to be the judge of the visual and tactile satisfaction of this type of panelling.
Liner materials
When choosing a wood-fired hot tub liner, there are three choices: polypropylene (least expensive), fibreglass (most commonly used) and acrylic (latest technology).
- Polypropylene liners were made to separate the bathing water from the timber exterior and enable water sanitation. However, plastic liners are the least durable option and have limited shapes.
- Fibreglass liners support their weight and can therefore be shaped for comfortable seating. They can be used with some water treatment chemicals, excluding chlorides, and can be repaired if cracked.
- Acrylic is even sturdier than fibreglass, scratch-resistant and compatible with sanitisers containing chlorine for water disinfection. However, acrylic liners cannot be fixed in the unlikely case of cracking.
Steel
While you should avoid any models that do not specify the alloy of the stove, most brands do inform you about what material composition they use. Here are the main types of steel used in wood-fired hot tubs:
- Aluminium does not corrode in clean water but it will get damaged when exposed to chemical compounds like bromine, chlorine, lime and cement solutions, or even chemicals present in tap water, such as fluorine, potassium and sodium.
- AISI 430 grade stainless steel cannot be used with chemicals in the water.
- AISI 304 grade stainless steel with nickel has increased corrosion resistance and lasts longer.
- AISI 316 grade stainless steel alloy has an even higher nickel content and includes molybdenum, which increases its corrosion resistance, especially from acids and chlorides.
Summary
In this guide, we have reviewed the key technology and material solutions available in the modern wood-fired hot tub market to help you make the right choice when considering which wood-fired hot tub to add to your home.
Each combination will come at a different price point and offer a unique user experience. Naturally, superior materials and design solutions will provide benefits as simpler maintenance, the ability to keep the water unchanged for longer periods and offer a sense of luxury – all of which are worth paying extra for. It is important to weigh up the advantages and disadvantages of each feature of a hot tub to decide what is most relevant for your needs. You may find that you are happy to compromise on some features while ensuring you have others.
Now that we’ve broadened your understanding of how a wood-fired hot tub works and everything that goes into constructing it, we’re ready to clock off and enjoy a nice soak ourselves. Hopefully, you can do the same once you’ve purchased your own wood-fired hot tub!
