Pool Spa Life
Pool Spa Life


There are several ways to heat a pool 

Despite Australia’s reputation as the land of eternal sunshine and long hot summers, most backyard pools benefit from the installation of a heating system. Swimming pool heating can significantly extend your swimming season — in some cases by months.

Much the same as air conditioning, there are ideal temperature setpoints for swimming pools, depending on the type of activity for which they are used. For leisure swimming, it’s between 24 and 26°C and a little higher for exercise, at around 28°C. Hydrotherapy pools are generally heated to between 30 and 36°C to deliver the optimum environment. Of course, these temperatures are not easily achieved without intervention and most pools sit somewhere between 18 and 22°C during the swimming season. Any heat gained during the course of the day is quickly lost after nightfall, leaving the pool cold again come morning.

One of the quickest ways of warming your swimming pool is to use gas heating, allowing you to extend the swimming season and enjoy the pool for longer, while also increasing return on your investment.

The increased availability of natural gas and LPG has made gas heating an increasingly popular choice. The use of Gas heating for Swim spas or Spas is very popular due to the quick response time to reach the required temperature.

How it works

Gas pool heaters use either natural gas or LPG. As the pump circulates the pool water, it is drawn from the pool and passes through a filter to the heater. The gas burns in the heating unit’s combustion chamber, generating heat which is then transferred to water that is returning to the pool.


Gas is ideal for heating quickly and the most efficient method for heating pools and spas in short periods of time, as they can reach the desired temperature quickly and maintain that setting regardless of ambient conditions.


The size of a gas heater is expressed by its input rating — a measure of its fuel energy consumption in megajoules (MJ) — and by its output rating measured in kilowatts (kW). Small heaters are in the range of 60 to 100 MJ and larger units between 250 to 400 MJ. Heater output ranges between 25 and 100 kW. Consider the following factors when determining the most ap-propriate gas heater size for your application:

  • Desired temperature — this is personal choice, but as a guide the temperatures above are suitable for each type of activity

  • Water volume — determine volume by multiplying the surface area (pool length x width) by the average depth including wading areas and spa (if applicable)

  • Acceptable waiting times — how long you are prepared to wait for water to reach the desired temperature

  • The use of heat-retaining accessories — whether you utilise a pool cover or blanket. When determining swimming pool water volumes, don’t forget to factor in the spa. Most people want to heat the spa more quickly (and to a higher temperature) than the pool, so the ultimate choice should take this into consideration. For applications that only require pool heating and time is less of an issue, a smaller heater may suffice.

Installation and operation

Gas heaters are available in a range of configurations designed to suit specific conditions, including indoor and outdoor positioning. In-door installations require fluing and adequate ventilation for the size and type of heater being used. Heaters designed for outdoor use should not be used indoors.

Though most heaters are designed and constructed to operate in all conditions, appropriate consideration should be given to protection from the elements and the manufacturer’s installation recommendations always followed. Heaters should be installed on a stable non-combustible base, preferably 50 mm or more above ground level.

Things to know and look for

Most gas heaters available today are fitted with thermostatic controls. Heaters connected to spas must have a thermostatic control with a maximum temperature set to 40°C.

As with other heating types, various makes and models offer differing degrees of control and options. While budget is always a consideration, be sure to factor in your lifestyle and usage patterns when assessing alternatives and be sure not to overlook any long-term benefits in favour of a short-term cost-based decision. If you aren’t sure, or would like further advice, consider speaking with a SPASA member, who can point you in the right direction.


Given the combustible nature of gas, there are specific safety considerations:

  • Chemicals — including pool chemicals — must not be stored in the same room as a gas heater

  • Spa blowers must be located a minimum of 1.5 m from an installed gas heater.

A final note: care should be taken when using gas heaters in salt chlorinated pools. ensure that the production of chlorine is adjusted to suit, as excessive salt and/or chlorine levels can damage internal components. this is particularly important when operating for extended periods during heat-up.

Australia’s solar power uptake rates are among the highest in the world, with some homeowners choosing to capitalise on that investment and add pool heating into the mix.

Australia’s dry, sunny climate lends itself to swimming pool solar heating, with many homeowners taking advantage of plentiful sunshine to power their homes and save on electricity or gas costs.

How it works

The specifics of the type of solar system you choose will vary, but the basic principles are the same. Pool water is circulated through the solar collector — a series of tubes generally mounted on the roof — where heat is absorbed and heated water is returned to the pool. The collector is constructed from either Polypropylene or a flexible PVC compound and is usually supplied in multiple tube strips or panels.


Harnessing the power of solar energy is an economical pool heating solution, allowing you to increase pool usage by up to four months, depending on your location. Beyond the initial outlay, annual running costs for a solar system are minimal.

Sizing, location and orientation

Obviously, the amount of heat absorbed is heavily dependent on the size, location and orientation of your solar system. There is a little more calculation and pre-planning required for solar heating than other alternatives: size and area, positioning and the type of solar controller to use.

The size of the solar collector is a major determiner of overall system effectiveness. It is usually expressed in square meterage and, as a general rule, relates to the surface area of your pool.

There is no hard-and-fast rule, as a range of variables will determine the square meterage required. These variables include local climate, shading of the roof or pool, type, colour, slope and orientation of the roof, wind protection and the collector type. Recommendations generally come with the proviso that they apply only in ‘ideal’ conditions.

Australian standard AS 3634-1989: Solar heating for swimming pools provides guidance for the minimum acceptable collector area in ideal conditions. This varies by geographic location and uses a simple estimation. A rule of thumb is at least 60% of pool surface area (length x width) for FNQ/NT, 70% for SEQ, Alice Springs/parts of WA and 80% for NSW, act, Vic, SA, TAS and Perth.

When higher than average water temperatures, longer swimming season or rapid heat response are the desired goals, opt for a larger solar collector area — this can be up to and over 200% of the pool surface. It is important to note that ‘area’ in this context means the actual collector strip area, not the roof surface area.

AS3634 details solar collector calculation methods as follows: Nx (W+D), where N = number of tubes, D = tube diameter and W = width between tubes. The maximum web width that can be used is no more than one tube diameter per tube.

Solar collectors can be placed in a northerly-facing position and if the site does not permit a north-facing orientation (perhaps due to the Solar PV electricity panels being there), the collector can be installed on any other roof orientation and the area should be increased to compensate as per AS3634. Ideally, the collector will be located in a position free from shade caused by trees, neighbouring houses and other structures for at least six hours per day.

Things to know and look for

Pumping requirements

A pump is required to circulate water through the solar system. You can elect to use the existing pool pump or opt for a dedicated unit. When using the existing pump, you will need to ensure the following conditions can be met:

  • The required rate of turnover of the pool water for filtration purposes must be maintained.

  • The operating pressure of the filter must not be increased above the manufacturer’s maximum pressure by the addition of the solar circuit.

  • The pump must have sufficient capacity to handle the static head and friction losses introduced by the addition of the solar collector circuit.

The average residential solar installation requires a minimum flow rate of around 100 to 200 litres per minute to operate effectively. In most circumstances this means that a dedicated solar pump is required. When assessing pump alternatives, check that the minimum design flow rate of the solar collector will be met and be aware that this will vary with the diameter of tubing being used.

Circulated water must be strained to avoid blocking the solar collector with dirt and debris. This requires use of a strainer when opting for a dedicated pump.

Solar controllers

Solar controllers make the operation of the Solar systems fully automatic. Temperature sensing control devices allow operation of the solar pump system only during times when heat can be gained. The more advanced controllers have the ability to cool the pool in the early morning hours if it had become too hot due to geographical location or excessive hot weather.

Handover and documentation

Once installed you should receive documentation that confirms the system has been installed and commissioned according to AS3634 and your contract. Handover documentation should include:

  • A list of all major system components, including the size and make of solar collector, make and model of the control system, components and pump.

  • Copies of all warranties as issued by the component manufacturers, along with warranties issued by the installer.

  • Operating, preventive maintenance and service instruction documents that describe start-up, normal running and shutdown procedures.

  • A record of the date of installation and the name and address of the installer.

A final note: Using a pool blanket will increase the benefits of solar pool heating as it traps in the heat and additionally minimises evaporation. Covers and blankets are available in a range of styles from simple manual types through to fully automated options.

Electric heat pumps are another popular choice, delivering warmer water even while the sun doesn’t shine. Electric pumps extract heat from the air and use it to produce hot water. They are available in two types: on/off and inverter.

How it works

Heat pumps feature three main parts: a fan, an evaporator and a condenser.

Water is circulated by the pool pump, passed through a filter and drawn through the pump heater. The heat pump draws in air and directs it across the evaporator. Refrigerant absorbs heat from the outside air and warm gas then passes through the pump’s compressor. The compressor increases gas heat and passes it through the condenser. The condenser transfers the gas heat to the cooler water circulating through the heater and that heated water returns to the pool. The hot gas returns to liquid form as it flows through the condenser and back to the evaporator, allowing the entire process to begin again.

On/off heat pumps are self-explanatory — they run at 100% heating capacity when on and 0% when off. Inverter heat pumps adapt compressor and fan speeds up or down depending on the pool temperature requirements, which can offer greater efficiency through reduced heating times and running costs.


The major advantage of heat pumps is that they are an extremely energy-efficient alternative. This is because the pump itself requires much less energy (in the form of electricity) to operate when compared with the amount of energy (in the form of heat) that it produces.

The energy efficiency is measured by coefficient of performance (COP), a ratio of energy consumption to production. COP is expressed as a whole number and the higher that number, the more efficient the pump. For example, a heat pump that consumes 2 kW of electricity that produces 10 kW of heat energy has a COP of 5.0. This is because for every kW of electricity it takes to run, it generates five kW of heat.


Swimming pool heat pumps are available in a range of sizes.

You’ll need to consider the following factors when determining the most suitable option for your application:

  • Location — ambient climatic conditions will have a huge influence.

  • Desired temperature — this is personal choice, but as a guide the following temperatures are suitable for each type of pool:

    • pools used for social swimming or exercise — 24 to 28°C,

    • therapeutic pools — 28 to 35°C,

    • spa pools — 34 to 38°C.

  • Water volume — determine volume by multiplying the surface area (pool length x width) by the average depth including wading areas and spa (if applicable).

  • Shading and wind exposure — both will affect the heat losses and gains of heated water.

  • Use of a cover - this will dramatically reduce the running cost and the required size of heat pump

  • Position — an indoor or outdoor location.

  • Desired season — determine if you would like to swim year-round or just to extend the season by a few weeks in autumn and/or spring.

Installation and operation

Heat pumps can be located indoors or out, as long as appropriate airflow and ventilation are available in the chosen location. Heat pumps use a fan to draw in air and to expel it, so adequate ventilation is required for indoor installations.

Outdoor installations can be positioned at ground level (a 50 mm plinth is recommended), mounted on a wall or on a roof.

Heat pump units can be included as part of the pump and filter network or plumbed as a separate heating circuit. An average-sized residential installation will generally require a single-phase electrical connection, whereas large pools may require three-phase power.

Where possible, consider an off-peak connection to further reduce running costs.

Things to know and look for

Swimming pool heat pumps will incorporate a flow control device to prevent operation when adequate water flow is not available.

Heat pumps are thermostatically controlled and most are available with Wi-Fi and Apps to give convenient control from a remote location.

As with all pool equipment types, not all heat pumps are created equal. Some will include additional features and controls such as timeclock and/or pump interlock which allow the user to ensure the most economical operation. Make sure you are comparing apples with apples when assessing alternatives. If you need more information or advice, speak with a SPASA member.

A final note: Care should be taken when using heat pumps in salt chlorinated pools. Ensure that the production of chlorine is adjusted to suit, as excessive salt and/or chlorine levels can damage internal components. This is particularly important when operating the heat pump for extended periods during heat-up.

The introduction of Inverter technology has become a popular choice for Pool owners. If you want to swim in your pool every day, require exercise regularly, or need warm consistent water temperatures for therapeutic reasons, an inverter heat pump is the ideal solution.

Inverter heat pumps deliver a solution that creates improved efficiencies and performance compared to the Standard On/Off type. The end result is a significant reduction in running costs and carbon emissions.

How it works

Operating on a similar principle to an air-conditioner system, an inverter heat pump absorbs the available energy from the surrounding air, and the electrical pump transfers the heat into the pool through a series of processes.

Energy efficiency

An inverter heat pump is one of the most energy-efficient electric pool heating systems available and produces far more energy than they consume.

They can produce up to 16 times more energy than what they consume. For every 1 kW of electricity used, up to 16 kW of heating can be produced. This is referred to as the COP (coefficient of performance). Realistically the average COP of a inverter heat pump will be somewhere in the middle (7-11x) as peak performance is heavily reliant on maintaining a set temperature continuously during warm, humid weather.

To achieve high COP’s the inverter technology continually optimises the way the heat pump operates to ensure that the least amount of energy is required to maintain the desired temperature, producing incredible efficiency and lower electricity bills. This allows for the desired pool temperature to be managed much more efficiently.

The motor works like cruise control in your car to maintain a set temperature, rather than stopping and starting the motor like traditional on/off heat pumps. The inverter heat pump runs at maximum capacity to get the pool up to temperature as fast as possible, but then automatically reduces its speed and energy consumption to maintain the temperature.

It is strongly recommended to limit the amount of Heat loss by using a pool cover and allowing the Heat Pump to maintain the desired temperature continuously. The more hours a Heat Pump is off, or the Pool cover is not on, then the harder the Heat Pump works to recover and the more expensive it becomes to run.

With excellent energy efficiency advancements, it makes sense that this can translates to low running costs. With care in sizing and adherence to best practice in operating the Units an inverter heat pump can cost up to 85% less to operate than conventional electric elements and up to 60% less than gas heating. 

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