Author: Oliver Smith

Gone are the days where the water had to be changed the day after enjoying a soak in your wood-fired hot tub. With technological advances, you can now maintain the water unchanged for days, weeks or even for a couple of months with the most modern units! Or at least, that’s what hot tub makers are saying, so let’s find out how they’ve made it possible and what you should know about preserving the quality and sanitation of the water in your hot tub for your ease and convenience.

The following factors affect how long you can keep the hot tub water in excellent condition and prolong the time between water changes:

1. Types of water filters used in wood-fired hot tubs
2. Liner vs all-wood
3. Water treatment chemicals
4. UV light purification

What are the typical water filters used in wood-fired hot tubs?

There are two types of water filters: cartridge and sand filter. Each type comes with its own advantages and disadvantages which we will explore below.

Cartridge filters

1. Size – A cartridge filter is more compact. It is usually integrated into the structure of the hot tub behind the exterior cladding, while some models can be hung inside the hot tub.

2. Durability – A cartridge will typically last for up to a month, but this is highly dependent on water quality and usage. Its life can be extended by regularly rinsing the dirt off until it becomes too dirty to wash or scrub.

3. Changing – Changing the cartridge is a breeze.

4. Cost – The cost of the water filtration unit itself is less than a sand filter. However, cartridges must be replaced much more often than the sand or filter balls in a sand filter, which slightly increases the overall running cost.

5. Fibre – The fibre used in filter cartridges today is non-recyclable, which means it is not environmentally friendly.

Sand filters

1. Maintenance schedule – Sand filters need their filtering equipment replaced less frequently. Once the filter has been filled with sand, you will be good for up to five years before the time comes to replace it. However, there is more work involved in changing the sand compared to a filter cartridge. In addition, with a sand filter, you’ll need to regularly perform the backwash operation by draining a small amount of water at a time.

Modern sand filters have been adapted to work with fibre balls, which offers significant advantages. First of all, filter balls are much lighter than sand. You will not need to perform the backwash, but filter balls require minimal washing once every three months. They can typically last for about two years.

2. Environment friendliness – Another benefit is that both sand and recyclable filter balls are environmentally friendlier solutions than cartridges.

Difference between wooden and lined hot tubs

Wood is a natural material which is very sensitive to water. When wood is overly dry, the joint areas tend to shrink and start leaking. When wood is left in contact with water for a long time, algae and bacteria can quickly build up, leaving the water unusable and unsuitable for bathing. When using sanitisers in a wooden hot tub, it is important to bear in mind that chlorine destroys lignin, the component in wood that strengthens its cell walls, and therefore the timber loses its integrity. As such, you have to be careful, to say the least.

For these reasons, plastic liners were invented to separate the wooden exterior from the water. Later, fibreglass became much more commonly used in the wood-fired hot tub industry, and acrylic liners have more recently made their way onto the scene.

In short, a wood-fired hot tub with a liner will offer better and more varied water hygiene options.

What wooden hot tub chemicals do you need to protect against microorganisms?

It can be easy to get confused with all of the different chemicals needed for water hygiene when you own a hot tub, but we’ve made it easy for you with our guide below.

First things first: for any sanitisers to work appropriately and kill the different microbial organisms in your hot tub water, you need regular testing discipline and pH level maintenance. Even before we get into the different types of sanitisers, make sure you have a pH tester (either strips or an electronic tester) and a pH increaser/decreaser to keep the hot tub water within the 7.2-7.6 alkaline range.

Next up, use water sanitisers to kill bacteria, viruses, algae and fungi. The most commonly used sanitiser is chlorine, which is easy to manage, cost-effective and eliminates pathogens. A downside of chlorine, in addition to its recognisable smell, is that it can be harsh to some hot tub parts and may cause skin or eye irritation. If these are issues for you, there are alternatives discussed further in this guide.

Some oxygen-based sanitisers require three separate agents for water sanitation: oxygen (tablets or granules), oxygen activator and algaecide for the full triple-action defence.

A water clarifier helps to keep the hot tub water clean and clear by attracting and enlarging tiny dirt or dust particles to assist the filter in capturing them.

Anti-foam agents fight water pollutants, such as perfumes and lotions, causing them to sink down so they can be trapped by the water filter.

Plumbing cleaner removes biofilm, scale deposits, grime, oily residue and other chemical, mineral and organic contaminants that may be present in the pipes of the hydromassage system (if present).

Chlorine or non-chlorine sanitisers

Make sure to be careful with chlorine if you are using it. Chlorine is the most common chemical utilised for hot tub or pool sanitation purposes. With hot tubs that have wood-fired stoves, however, this is not necessarily the case. The reason for this is that these stoves can be made from different types of steel with varying anti-corrosive properties. Simply put, the cheaper the steel, the more sensitive it is.

Steel AISI 430, for example, which is used in the most economical wood-fired hot tub models, has both lower durability and resistance to chemicals. The same goes for aluminium, which can be easily 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. However, don’t get discouraged about either AISI 430 or aluminium, as they are perfectly safe to use with chemicals other than chlorine.

Steel AISI 316 is a stronger type of steel that is guaranteed to resist the effects of chlorine or seawater. 

AISI 304, the in-between steel variation, is also effective when used with chlorine, although it is more susceptible to pitting when exposed to chlorine at higher temperatures.

It is critical to understand the different materials used for the metal parts of a wood-fired hot tub when you are deciding which chemicals to use for water sanitation purposes. If you have sensitive skin, you should take extra care with the chemicals you choose, and it is recommended that you do not use chlorine.

Chlorine sanitiser alternatives include:

• Bromine – This acts even more effectively at high temperatures and does not produce gases that irritate skin as chlorine does.
• Oxygen-based – These sanitisers are milder mineral solutions, which makes them perfect for sensitive skin and they will not cause any structural materials of your hot tub to deteriorate. However, they require slightly more effort and regular maintenance.
• Biguanide – Kills bacteria just as well as chlorine and bromine, only it’s more expensive and may cause deterioration of rubber or plastic parts. Ensure you check with your hot tub manufacturer before using any biguanide sanitisers.

UV to augment the effectiveness of sanitation chemicals

Ultraviolet (UV) light disinfection systems help to protect bathers against pathogens, such as moulds, viruses and bacteria.

UV radiation prevents various microorganisms from reproducing or even kills them. This form of radiation also destroys floating algae. As a result, the clarity of the water is greatly improved.

Please note that the UV light alone will not sufficiently neutralise all microorganisms present in the hot tub water, and therefore it must be used together with sanitisers for maximum effect. The good news is, however, that with such a system, the amount of chemicals needed can be reduced by up to 80%! This makes it both an economically and environmentally efficient feature in a wood-fired hot tub.

Hot tub water treatment requires more than just a single chemical to keep it clean and hygienic. Whether you should go with the more traditional chlorine or gentler options depends on factors such as skin sensitivity and the materials used in the design of your hot tub.

The go-to system we typically recommend involves oxygen-based sanitisers + UV disinfection since this combination can be used with just about any type of wood-fired hot tub, and they don’t produce any unwanted smell or skin irritation. An added benefit is that you also won’t kill the garden plants when watering them with the water you drain from your hot tub!

We hope all this information helps you to decide on the best choice for water maintenance in your hot tub. Stay safe and happy soaking in that fresh, clean water!

Wood-fired hot tub manufacturers such as Kirami, Royal Tubs, Skargards and others never miss a chance to boast their state of the art, faster than ever water heating time, which is typically three to six times quicker than that of electric heaters.

Hot tubs with electric heaters, on the other hand, are virtually instantaneous. Once installed, they need nothing more than to be plugged in and turned on to heat up the water. To compete with electric heaters, wood-fired hot tub producers have innovated solutions that provide hot tub lovers with a combination of the two. Read on to discover how a hybrid wood-fired and electric heating system works, what its capacity is and whether all top wood-fired hot tub brands in the UK offer it.

Why use a hybrid heating system in a wood-fired hot tub?

For wood-fired hot tubs, low-powered electric heaters are primarily used to maintain the water temperature once it has been heated by the main wood-fired stove and to prevent water from dropping to freezing temperatures in winter.

Wood-fired and electric heating systems can be effectively combined into a hybrid approach, so there’s nothing to stop you from using both heaters at the same time to speed up the water heating process. Since wood-fired hot tubs already achieve fast heating, the hybrid system cuts that process down even more for excellent results.

Below are the three key practical benefits of a hybrid wood-fired and electric heating system in a hot tub:

1) You can use the electric heater when you are unable or have no time to use the wood-fired stove.

2) You can rapidly heat the water in the hot tub with the wood-burning stove, then comfortably maintain the temperature with the electric heater for hours or days on end without needing to stoke the stove with an extra log or re-fire it.

3) You can switch the electric heater on when subzero winter temperatures are approaching. You can maintain the water temperature above 8°C, so you can rest assured there will be no damage caused by frost, and you won’t have to drain the water.

How do electric heaters combine with wood-fired stoves?

In a hybrid heating system, the electric part of the duo will typically be installed by the water filter that serves as a water pump to circulate water through the heater. Some systems may be designed to use the water circulation of the hydro massage system, or the electric heater may have its own dedicated pump. The point is that the electric heater will only do its job when water is circulated through it.

Another benefit of an electric heater is that it is compact and easy to control. Most feature a thermostat which allows you to select the desired temperature level. Some have an automated switch that enables them to respond to thermostat readings, while more basic models may require you to manually plug them in to set them to work.

Can an electric heater do the job alone?

Over a period of approximately 20 hours, an electric heater of around 3kW  can bring the water up to a toasty temperature for the ideal dip, consuming some 60kWh of electric power. In winter, this heating time can be longer, so it just depends on your level of patience and how far your power budget extends.

We note that we are unable to produce exact numbers for how long you would need to wait for an electric heater alone to heat a wooden hot tub since these figures are highly dependent on factors such as the size of the hot tub, time of year, mains water temperature, level of hot tub insulation and the capacity of the heater itself.

Taking a practical example from our own experience, we found that a six-seater hot tub containing approximately 1200 litres of water took us 22 hours to heat with a 3kW electric heater in winter with an outside temperature of 0°C.

What is the capacity of an electric heater in a wooden hot tub?

Wood-fired hot tub makers are unlikely to risk the need to add in a special electric power installation for you to house in your garden, so the electric heaters used typically consume low levels of power, varying at around 3kW. Such heaters can be connected to a regular power outlet to get them going.

The top wood-fired hot tub brands in the UK offer the following options for hybrid heating:

Skargards – 2kW

Gardenvity – 3kW

Royaltubs – 3kW

Kirami (The Log Company) – 2.3 to 3.3kW

Timberin offers a uniquely wide variation of electric heaters. The standard model starts at 6kW which can be upgraded to 9, 12, 15 or even 18kW! In addition, Timberin offers a more cost-effective solution of a floating 300W electric heater to prevent the water from freezing.

How can you improve the efficiency of your heating system?

Lined wood-fired hot tubs can be insulated to help you save on firewood and keep the water warmer for longer. This can be a wise decision to make as a hot tub owner, as adding polyurethane insulation only costs approximately £150 extra. Reviews left by hot tub owners indicate that this extra insulation is a worthwhile investment, as it keeps the water warm for notably longer periods.

Another essential part or accessory of a wood-fired hot tub to maximise heating efficiency is an insulated cover. Whether or not this is included in your hot tub package depends on the manufacturer, as in some cases you may have to purchase it as an additional accessory yourself. As we’ve learned ourselves, an insulated cover is a game-changer for hot tub heating. It speeds up the heating process and keeps the water warmer for longer since a hot tub has a considerable surface area, causing it to quickly lose heat if left uncovered. When deciding on a cover to purchase, you can choose between plastic, wooden or insulated faux-leather lids. The latter produces the best result.

Summary

The key benefit of a hybrid heating system that combines both a wood-fired stove and an electric heater in a wood-fired hot tub is the comfort and convenience it brings to quickly heat the water and maintain it at an optimum bathing temperature for as long as needed, with no additional work required.

This hybrid system also gives you the confidence to keep using your hot tub throughout winter. When you keep the electric heater on, you can rest assured that your hot tub will not be susceptible to frost, which can get into the water circulation system and damage your hot tub.

A further benefit is that the secondary electric heater can shorten the water heating time. What’s more, it does this without requiring any additional power outlet installation from your side. Plus, if you’re patient enough, you can even heat the water with the 3kW heater with just the flick of a switch.

While a hybrid heating system may not be a must-have for every hot tub owner, it is certainly a worthwhile investment for extra convenience and hands-free operation.