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Heating pool & spa water

An array of options

Once the aforementioned information has been gathered, it is time to narrow the client’s options. With so many choices, it is important for builders to understand the pros and cons of each, and be able to relate that information to their clients.

Fossil fuel (natural gas or propane)

Pool cover
There are many benefits to covering pools. The main advantage is minimizing heat loss due to evaporation, while other fringe benefits include cleanliness and lower chemical usage.

Fossil fuel heaters are generally very quick in providing on-demand heat and are inexpensive to install the gas and venting connections. These systems are a common mid-range efficiency pool heater that is one of the lower priced units on the market today. However, they can be more expensive to operate (increasing cost of gas), have higher emissions and must run at higher temperature ranges for optimal performance.

As they are mid-range efficiency class heaters, the output of gas and emissions is something that should be discussed with the customer. The other thing to consider is when running pool water temperatures below 15.5 C (60 F), with colder outside temperatures, it is hard on a gas heaters, as they condensate from the temperature difference in the heat exchanger. Condensate then drips onto the burner causing premature failure. Therefore, these heaters are not intended to run lower temperatures for extended periods of time.


There are a few pros to using an electric heater. Generally, they are inexpensive to operate and create no emissions on site. They can also run at various temperatures without causing damage to the heater. On the other hand, electric heaters place a significant demand on the household electrical supply and require an expensive initial installation.

Often the case with new and/or existing homes, the main electrical panel is not large enough to provide the amperage needed to run an electric heater without the need to install additional amperage. Wiring sizes and potential electrical upgrades can make electric heater installation become expensive.

Air/water heat pumps

Heat pumps are efficient and heat pool water inexpensively. These systems draw in outside air, which is passed over an evaporator coil containing a liquid refrigerant. As heat is absorbed, the liquid turns to gas, which then passes through the compressor and condenser where heat is transferred to the cooler pool water circulating through the heater.

Heat pumps, however, are more expensive than standard heaters and have higher electrical demands. They can also take more time to initially heat the pool depending on the ambient outside air temperature (i.e. when the weather is cold, the heat pump does not work as well).


Geothermal heating systems are efficient, can be used year-round and are an environmentally conscious choice, as they draw heat from underground or water to water, via heat exchangers and transfers it to the pool.

During the summer, when the house is being cooled, geothermal systems also allow the heat extracted from the home to be dumped into the pool to heat the water. Usually these systems do not have a carbon footprint and have a very high return on investment (ROI) with regards to the electricity used to operate the system versus the heat generated.

Due to the high costs involved in retrofitting an older home, geothermal heating systems are mainly used in new home construction.

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