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How do Hot Tubs Work?

If you're curious to know more about your hot tub then look no further. In this article we explore the mechanics of hot tubs and get to know how they work.
couple in hot tub
The basic principle of hot tub function is that water is warmed by a heater which is then circulated around the hot tub and pumped through aerated jets to provide a soothing sensation for its inhabitants.

To get the water into a hot tub you will need a garden hose or tap. The water inside your hot tub is treated regularly to prevent bacteria growth and replaced when necessary. The way hot tubs are filled is sometimes a cause of confusion for new hot tub owners ; many believe the water is pumped continuously into the hot tub through a mains water source. This however is not the case. Home hot tubs are filled and emptied seasonally and maintained through the use of sanitization chemicals.

Crucial Components

Hot Tub Filter

Hot tubs also contain a filter (some large hot tubs may contain two). The filter helps to clear and water of contaminants that may interfere with the water's clarity or cause blockage of the jets. Hot tub filters also help to draw out large particles of detergents such as cosmetics and soaps as well as natural oils from hair and skin. The filter plays a very important role in keeping the hot tub clean and assisting the sanitization chemicals can properly do their job.
hot tub filter

Hot Tub Pump

Most hot tubs operate using two pumps. One pump is responsible for cirulating the water through the heating and filtration system while the other sends water supply to the jets. In some hot tubs there may even be three or more pumps.

In home hot tubs, water should be circulated throughout the spa at a minimum of 2 to 4 hours twice a day. It is also possible your spa operate with a 24 hour energy efficient pump. How often your pump runs will depend on your hot tubs design however it is essential the pump operates to circulate the water regularly. Regular circulation of hot tub water is essential as water is constantly moving through the filter where impurities can be removed. Regular circulation also helps the water throughout the hot tub stay a constant and even temperature, with no hot or cold spots.
hot tub pumps

Heating Element

Most home hot tubs use an electrical heater to heat up the water. However, other methods of heating can also be found such as wood burning and even solar power. Electrical heaters on the other hand tend to be more accurate and allow for better temperature control.


Hard shell hot tubs are fitted with jets. These jets pump water and air into the hot tub which creates the massage experience hot tub users love. Most hot tubs are equipped with two types of jets: high pressure pin jets and low pressure massage jets. The high pressure pin jets are smaller in diameter and push out less water. However, the high pressure still feels good on the skin. Low pressure high flow jets on the other hand are thought to offer a more effective massage, with the theory the higher water flow is able to stimulate below the derma layer. Therefore, when it comes to hot tubs, it is not the amount of jets fitted that will offer the best experience, but rather the quality of each jet.
hot tub and jets picture

How does it all work?

Hot tubs run using a closed loop system. This means the same spa water is cycled throughout the spa over and over again until it is replaced. Keeping the water cycling constantly is important as it prevents stagnation and allows water to continuously run through the filter where dirt and bacteria can be removed from the water flow.

Hot tubs are electrically powered. To acquire this power they can either be plugged into a standard domestic mains outlet or wired directly to the home's electricity supply by a qualified electrician. Hot tubs which plug directly into the mains are typically referred to as 'plug and play' hot tubs. Plug and play hot tubs tend to be smaller than non plug in hot tubs as they must be 13A or under.
woman in hot tub


All hard shell hot tubs contain a heating element. This element is responsible for warming the water to a desired temperature.


To operate, hot tubs use suction, filtration and return inside a closed loop system.

First, water is taken in through a floor drain and skimmer and into a suction line. The skimmer sits just below the water's surface and is often concealed to look like a jet. The suction line is the start of the circulation process. Once water is taken in, it is sent to the pump. The pump then pushes water through the filter or heating element. Depending on the type of filtration system being used, the water may pass through the heater or filter first.

Once the water has made its way through the suction line, heater and filtration system it may then pass through an ozonator (if the hot tub is fitted with one). Ozonators are an additional method of filtration and sanitization. They work by injecting ozone gas into the water. This reactive gas helps to break down pollutants and kill off bacteria.

Finally, the water makes its way through the hot tub's return line. The return line is typically a PVC pipe which ends at a manifold diverter. Here, the clean, heated water is pumped through the diverter to various points inside the hot tub.


Unlike the circulation pump, the secondary jet pump functions under the instruction of the control panel, which is managed by the hot tub user. When the user decides to switch on the jet function, the pump takes in a water and air mixture, which is then pressurised and sent into the hot tub through the jets.
Woman sat in hot tub
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