Building and maintaining a pool is very costly. If it is then too cold to use it becomes a pretty poor investment. Adding a heating system will completely transform your swimming experience. With modern pool heating systems one can relax in a steaming hot pool, even in the middle of winter, or simply heat the water to a temperature where you and your family can stay in the pool for hours, without getting cold.

There are a number of different technologies that are commonly used to heat swimming pools and jacuzzies. With this article we aim to provide an unbiased look at the advantages and disadvantages of each of these technologies. Let’s however first start with some basic.

Pool Heating Basics

  1. Pool Thermal Blanket

    The majority of heat loss occurs on the surface of a pool. If the ambient temperature is lower than the pool temperature your pool will cool down. This gets much worst when even a slight breeze is blowing over the surface of the pool. The higher the thermal loss, the harder the heating system will have to work in order to maintain the desired temperature. Covering the pool with a thermal pool blanket will drastically reduce the effort and size of the heating system. This applies to indoor swimming pools as well, as the evaporation from the surface of the pool will cause heat loss and high levels of humidity inside the building. If, for some reason, a thermal pool blanket cannot be used, you would potentially need a heating system that is at least twice as powerful as the recommended system. This is however dependent on how hot you want your pool to be and how much wind you have on the surface of the pool. If you are only interested in raising the pool temperature to a few degrees above ambient, the effect is less dramatic, provided of course, that there is no surface wind.

    Preventing thermal loss is not the only benefit of having a pool cover or a thermal blanket. The correct type of pool cover will also substantially reduce evaporative water loss, filtration pump time and chemical usage and is therefore maybe not a bad idea even if you are not interested in a heating your pool. Please note that we do not sell, nor do we generate any income from promoting pool blankets. In fact, we would make more money if you do not use a blanket because you will need a bigger heating system.

  2. Installation

    All pool heating systems are connected to the pool in the same way. The heating system is installed in-line with the pool filtration system after the filter but before any chemical dosing device, like a chlorinator, for example. The reason for this is that you do not want concentrated chemicals flowing through your heating system.

  3. Pool water outlet

    In order for your pool heating system to efficiently heat the entire pool, it is ideal to have deep water jets or outlets at the bottom of the pool, as opposed to surface or shallow outlets, since hot water rises. If your pool is fitted with surface outlets launching horizontally, you will experience higher thermal losses and longer heating time of the deeper water. In order to overcome this challenge, you can either turn your jets to face downwards, or fabricate a simple downward outlet that attaches to your jets by connecting a 50mm, 90° downward elbow to a length of pipe, with another 90° elbow facing outwards.

Pool Heater Options

A. Electrical Element Pool Heating

This method simply uses an electrical element to heat the pool. The element is relatively cheap but water heating requires a lot of energy and so the electrical running cost is very high. Because of this the practical usage of this type of heating is really limited to infrequently used small Jacuzzis.

B. Gas Pool Heating

In this instance LPG gas heaters are installed to heat the pool. The units are relatively expensive for typical domestic size pools, but becomes more cost effective when you get to Olympic size pools. The running cost of a gas pool heater is more expensive than an electric element pool heater. Gas pool heating will only make sense as if you need to heat a pool in a place where there is no sunshine, electricity or a generator. A life expectancy of up to 10 years can be expected on a good quality unit that is well maintained.

C. Solar Pool Heating

The most common solar pool heater uses unglazed solar collectors, and the water from the swimming pool is simply pumped via the solar collectors to heat the water. The collectors usually consist of a network of black plastic pipes or a black plastic sheet. The upfront cost is higher than that of an electrical heater but, cheaper than gas heaters. The swimming pool filtration pump is usually strong enough to pump the water via the panels, which means the running cost of this system is basically zero. Since the output temperature of these systems are dependent on the sun and ambient temperature, you will not have a steaming hot pool in the middle of winter, but your pool can easily reach a comfortable, warm temperature like 28°C for 6 to 9 months of the year. The relatively low cost locally made panels will last about 5 years while a premium product like Heliocol has a proven lifespan globally of more than 20 years.

D. Heat Pump Pool Heating

A heat pump extracts heat from the surroundings air and converts it to higher temperatures. Heat pumps require electricity to operate but typically produces five times more thermal energy than the electrical energy it consumes when operated at pool heating temperatures. The upfront cost is about the same as that of gas heaters for domestic size pools. The electrical running cost is around a fifth of that of element heaters, which really makes it the only cost-effective option for heating your pool during winter. Even in a place with no electricity, it would be cheaper in the long run to use a generator or solar electric system combined with a pool heat pump than a gas heater. Heat pump units up to about 25kW in output power are still available in single phase input power, but for units bigger than that you would need a three-phase power source. A lifetime of approximately 10 years can be expected on a good quality unit that is annually serviced. Servicing the heat pump is mainly just making sure the evaporator is clean and free from debris.

A Practical Example

Let’s say we have a pool that is 6m x 4m with an average depth of 1.5m (36 000 L). The desired pool temperature is 28°C and the pool has a pool blanket on. We will assume an annual average thermal loss of 72kWh/day. We will also assume the client pays R3/unit (kWh) for electricity and R38/kg for LPG gas.

For electrical element heating we would require around a 9kW unit and that costs about R4000 and a power connection that can handle this! The running costs will be more than R78 000/year and you will need a three-phase power supply.

For a LPG gas heating system we would also require around a 9kW thermal output unit which costs about R20 000. At 85% efficiency the unit will consume around 6.26kg of LPG per day. The running costs will be more than R86 000/year.

For solar water heating you will need about 12m2 of a high-density solar panel like Heliocol or 24m2 of the common locally made panels, and it will costs about R10 000. The running cost is basically zero. The system will however only be able to heat the pool to the desired temperature for 6 to 9 months of the year since the performance is dependent on the sun and ambient temperature. Figure 1 shows what can be expected form a properly sized solar pool heater with and without a thermal pool blanket.

pool-temperature-usage-chart

For heat pump heating you would need around a 13kW thermal output pool heat pump since a pool heat pump’s output power capacity is dependent on the ambient temperature. A unit like this will cost you about R20 000. The running costs will be around R15 500 per year.

Conclusion

From the above it should be clear that the only sensible options are solar or heat pumps.

Heat pumps are really the only option for people who desire a warm pool in the middle of winter or simply do not have roof space for solar pool heating panels. For that privilege you will however have to make a monthly “contribution” to Eskom’s well-being. If you however have a PV electric system that produces too much power, you can “dump” it into the pool heat pump.

If you simply want to get the most out of your pool for six to nine months of the year and you are not interested in swimming in the middle of winter, nothing comes close to a good quality solar pool heater.

On bigger and very frequently used pools combining solar pool heating and a heat pump gives you the best of both worlds. The solar system will provide free energy from the sun while the heat pump will do the temperature top-up when required. It is important to use a solar pool heating system controller on a system like this to ensure maximum gain from the solar system and also to prevent the heat pump from waisting energy on the solar panels during cold days.