Wood Fired Hot Tub Heat Up Time And 3 Easy Temperature Control Tips

Many people often have some questions before buying a hot tub, such as how long does it take to heat up? How to accurately control the water temperature? This article will take you to explore the Wood Fired Hot Tub Heat Up Time , key factors affecting heating time, and practical temperature control techniques, so that you can solve these questions faster.

How Long Does It Take to Heat up a Wooden Hot Tubs?

How long does it take to heat cold water to a suitable temperature for bathing? This section introduces the heating time of Alphasauna Hot tub built-in and external wood stoves and electric stoves for reference.

Heating Structure Type

There are two main installation methods for hot tub wood stoves:

Built-in wood stove: The stove body is placed directly inside the hot tub, usually made of stainless steel, and the stove wall is directly in contact with water for heating. This design has high heating efficiency and heats up faster than an external stove. but the stove body occupies part of the space inside the tub.

External wood stove: The stove body is installed outside the tub and connected to the tub body through two upper and lower circulation pipes. Cold water enters the stove from the lower pipe for heating, and hot water flows back from the upper pipe into the tub, forming natural heat convection. Although the heating speed is slightly slower, the space utilization rate is higher, the safety is better, and it is easy to maintain.

Wood Fired Hot Tub Heat up Time: Built-In Stove

Take the Alphasauna circular hot tub with a diameter of 1500mm*1000mm as an example. The tub is equipped with a seat structure and a built-in wood stove, which occupies about 30% of the space. Therefore, the actual water capacity is about 1050 liters, suitable for 2 to 3 people.
In terms of heating, the tub is equipped with a built-in wood stove with a power of about 15 kilowatts. The wood stove efficiently conducts heat to the water in the tub through the metal furnace wall, which can heat cold water from about 15°C to 40°C suitable for bathing, that is, a temperature increase of 25°C. Under ideal combustion conditions and correct operating conditions, it takes about two hours to reach a suitable bathing temperature.
Formula:
Required heat
Q = 4.186 × 1050 × 25 = 109,865 kJ
Time
t = 109,865/15 × 0.75 × 3600 ≈ 2.71 hours

Wood Fired Hot Tub Heat up Time: External Wood Stove

Take the Alphasauna circular hot tub with a diameter of 1500mm*1000mm and an external wood stove as an example. It is a medium-to-large tub type, suitable for 3-4 people. The external stove does not occupy the space inside the tub. Compared with the hot tub with a built-in wood stove of the same size, the usable space inside the tub is larger, and the effective water capacity is about 1200 liters.
It uses an external wood stove with a power of about 12 kilowatts. Under standard conditions, such as moderate temperature and sufficient combustion, it takes about 3.5 hours for this 12kW stove to heat up from 15℃ cold water to about 40℃ bathing temperature, that is, 25℃.
Formula:
Heat required
Q=4.186×1200×25=125,580kJ
Time
t=125,580/12×0.75×3600≈3.87 hours

Hot Tub Electric Stove

Take the Alphasauna electric heater bath tub with a diameter of 1500mm*900mm as an example. Its actual water capacity is about 1200 liters, which is suitable for 3 to 4 people. The tub is equipped with an external electric heater with a power of 6 kilowatts, which can efficiently heat the water to a suitable temperature for bathing under standard conditions. In contrast, the electric heater only has a constant temperature function and cannot complete the initial heating, so it is more suitable for maintaining water temperature.

Which Effects Wood Fired Hot Tub Heat up Time?

Of course, the actual heating time will be affected by many factors, including the water volume, the power of the heating equipment, the initial water temperature, the ambient temperature, and whether the insulation cover is used. The following are several factors that have a significant impact on the heating time.

Water Capacity

The more water in the barrel, the more heat is needed for heating, so the heating time will naturally be longer. For example, compared with an 800-liter barrel and a 1,200-liter barrel, the 800-liter barrel will heat up faster using the same heating furnace.

Power of the heating equipment

The greater the heating power, the faster the heating speed. Wood stoves usually heat faster than low-power electric stoves due to their high combustion temperature and strong thermal conductivity. In addition, built-in stoves and external stoves also differ in the way of heat conduction. Built-in stoves are in direct contact with the water body and have higher thermal efficiency.

Initial temperature of water

In summer, the water temperature is high and it takes a short time to heat up to the appropriate temperature; in winter, the starting temperature is low, so it takes a longer time to heat up.

Whether to cover with insulation cover

During the heating process, if the barrel mouth is completely open, the water surface will continue to contact with cold air, and a large amount of water vapor will be emitted, and heat will be easily lost, especially in autumn and winter or when used outdoors.
After adding the insulation cover, the heat can be effectively stored in the barrel, and the steam will not dissipate quickly, so that the water temperature rises more concentratedly and quickly. In addition, without heating, the insulation cover can minimize the drop in water temperature and achieve the effect of insulation.

Liner Material

Stainless steel: It has the best thermal conductivity. It can quickly transfer the heat generated by the stove to the water body. Therefore, under the same stove power, it has the fastest heating speed. It is especially suitable for use in cold environments and can effectively shorten the overall heating time.

Swimming pool membrane: Although it does not have the advantage of metal thermal conductivity, it is thin and has low heat transfer resistance, so the actual heating efficiency is relatively good, which is a choice with relatively balanced thermal efficiency.

How to control the temperature of a wood stove?

Real-time monitoring of water temperature changes

Alphasauna recommends installing an external water thermometer for the tub, such as a float type or a metal probe type, so that the temperature can be monitored without manual testing to avoid burns, and it is also more convenient. It is recommended to stop adding wood and reduce the firepower when the temperature reaches 38-40℃ to prevent the water temperature from rising rapidly.

Control the rhythm of adding wood

It is recommended to concentrate on adding wood and burning at the beginning of heating to achieve rapid temperature rise; when the temperature approaches the target value, reduce the amount of wood or use harder wood instead, which burns more slowly. This will make the temperature rise more gradually and easier to control. Do not continue to add a large amount of wood when the water temperature is close to the target temperature, otherwise it is easy to lose control of the temperature.

Use a heat preservation cover

It is recommended to use a heat preservation cover during the heating stage or when maintaining the temperature. This can not only effectively reduce heat loss, but also maintain the temperature after the stove firepower is reduced.
When using a wood stove to heat a hot tub, temperature control requires certain experience and operating skills. If the temperature is too high, it may cause skin burns; on the contrary, if the temperature is too low, it will affect the comfort of bathing. Therefore, when using a wood stove, if you want to effectively control the water temperature, the key lies in “observation, effective control and the use of auxiliary tools.”

How to Control the Temperature of an Electric Furnace?

The way to control the water temperature of the electric stove is relatively simple. The electric heating system is equipped with a control panel to set the heating temperature. In 2025, Alphasauna launched a new hot tub, which uses a dual heating system, heated by a wood stove, and controls the control panel to keep the electric stove constant temperature, improving convenience and user experience.

FAQ By Alphasauna

What Are the Key Factors That Affect the Heating Time of a Hot Tub?

Key factors include heater power, water volume, insulation, ambient temperature, etc.

Is Your Hot Tub Suitable for Outdoor Use All Year Round? Will It Heat up Too Slowly in Winter?

Our hot tub takes full account of seasonal and outdoor needs in terms of structure and material design. For low-temperature outdoor environments, we recommend using stainless steel or pool membrane liner, combined with a high-power external furnace, and an insulation cover, which can significantly improve the heating efficiency in winter.

Can the Use of an Insulation Cover Really Significantly Shorten the Heating Time?

Indeed, the role of the insulation cover is very obvious. It can effectively reduce the loss of heat from evaporation on the water surface and significantly improve the heating efficiency. When heating outdoors, the heating time can be greatly shortened after the cover is added, and the water temperature can be maintained for a longer time after the heating is stopped.

If I Have Some More Complex Customization Plans, Can Alphasauna Customize Them?

Of course. We provide a full range of customization services, covering size, barrel structure, liner material, heating method and accessory details, and support OEM/ODM customization. No matter how many people you need a hot tub for, we can customize it for you. In addition, our professional team will provide professional suggestions based on your actual situation. If you need to purchase a hot tub, please contact us.