There are many methods available for heating your swimming pool water, all with advantages and disadvantages. When shopping for a pool heater, keep in mind that different methods will be better for different swimming pools. When looking at options, consider the environment of your pool as well as the features of the heater.

In this article, we’ll be taking a close look at electric heaters. There are two types of electric swimming pool heaters: electric resistance pool heaters and electric heat pump pool heaters. A significant difference between these two types of heaters is that one creates heat (resistance heaters) and one captures heat and moves it, but doesn’t generate it (heat pumps); this will impact how your pool is heated and how the temperature maintains.

Electric Resistance Pool Heaters

Because resistance pool heaters use electric currents to create heat, these types of heaters are very inefficient and consume electricity in large amounts. Water heats by washing over a metal resistor that has been heated by an electric current.

Due to its need for large amounts of electricity, these types of heaters are very costly to install (requiring large-amperage circuit breakers and heavy wiring) and operate. As a result, you’ll most often see these in small therapy pools or spas.

Electric Pool Heat Pumps

There are two different types of swimming pool heat pumps: water-source and air-source. Let’s take a look at the two different types of electric heat pumps and what you need to consider when purchasing.

Water-source Swimming Pool Heat Pumps

Water-source swimming pool heat pumps (also referred to as geothermal heat pumps) have newer technology, and with higher efficiency and lower operating costs, they are growing in popularity. In particular, they benefit pools used year-round or in temperatures below 60 degrees because the temperature of the air does not affect their operation or efficiency.

Water-source heat pumps transfer heat from a water source to your pool water. Source water passes over a coil and heats a liquid refrigerant called Freon. The source water then exits the evaporator and goes back to its source.

Meanwhile, the heated Freon goes through a compressor, which makes it even hotter. Next, the Freon goes through a condenser while the pool water enters and exits the condenser. As the pool water goes through, heat is transferred from the Freon, cooling the refrigerant as it exits. Rinse and repeat.

There are different types of water-source heat pumps because there are many different bodies of water:

  • Open loop: This type of heat pump has two deep wells, one supplying water to the heat pump and one to which the water returns. Make sure you wells are deep, or the well will draw down loose soil and clog the system.
  • Closed loop: This system uses the ground for heat, instead of the water. Also known as a ground loop, this heat pump uses a mixture of water and antifreeze that runs through plastic tubing, collecting heat from the ground. This mixture then heats the evaporator coil. Closed loop systems are either deep and narrow (vertical closed group) or wide and shallow (horizontal closed group).
  • Surface water: Considered an open loop system, in this system water, comes from either fresh- or salt-based sources.  Due to that surface source, this type of heat pump usually requires more maintenance to keep the heat exchangers free from clogging from organic materials.
  • Mechanical loop: This setup uses water to remove heat from an air conditioning system that removes indoor heat waste before transferring it into the water loop. The loop is cooled with a cooling tower that is usually installed on the roof. This system supports the air conditioner by removing the waste heat, making it more efficient.

American Standard 9075.120 Safe-T-Heater
  • Whirlpool accessory
  • Maintain constant water temperature
  • Allows for longer, more relaxing soak

Pros and Cons of Water-source Heat Pumps

Because heat pumps only transfer heat, instead of producing it, water-source heat pumps are extremely energy efficient. With a longer lifespan, ability to install indoors or outdoors, low operating costs, and quiet operation, the water-source electric heat pumps make a small environmental footprint. Water-source heaters are great for colder climates and can extend the swimming window into the spring and fall.

Water-source heat pumps are more expensive ($2,000 – $4,000) compared to gas heaters (many available for under $1,500), and while more efficient are slower to heat. On the other hand, the heat pump costs are typically between $50 and $150 per month and their lifespan can be up to 10 years.

Air-source Electric Pool Heat Pumps

Air-source pool heat pumps are more effective in warmer environments and when used on a regular basis. Air-source heat pumps are sometimes called reverse-cycle heat pumps because they can be used to heat and cool your swimming pool, making them ideal for hot climates and year-round swimming pools.

An air-source heat pump is similar to a refrigerator or air conditioner, using the refrigerant to carry the heat to a compressor, then operates as a reverse air conditioner before transferring the increased heat to your pool’s water. While air-source pool heat pumps operate at less than half the cost of gas pool heaters, they are limited to climates with outside temperatures of 50 degrees or more. Below that temperature and there is no heat to withdraw from the air.

Pros and Cons of Air-source Electric Pool Heat Pumps

Although more reliable and efficient than gas heating systems, electric pool heat pumps are more expensive to purchase and to install (they require a breaker size of 30-60 amps with a dedicated circuit).

However, over the long term, heat pumps consume less energy than gas, so your heating bills will be lower. With heating costs up to six times less, heat pumps are a better investment than gas at a rate of $.63 an hour versus $3 – $9 per hour.

When maintained, a heat pump can last for 10-15 years; gas pool heaters average a 5-year lifespan. One other benefit is that the gas-powered heaters emit carbon dioxide so using an electric pool heat pump will reduce your carbon footprint.

How to Size Your Pool Heat Pump

When looking at the size of electric heat pump you want for your swimming pool, you will need to consider several factors. First, match the heater BTU output to the size of your pool in gallons. The larger the pool heater, the faster it will warm your water.

Smaller heaters are slower to heat and have to work harder, shifting purchase savings to higher running costs. If your pool is in a windy or colder area, or you don’t have a pool cover, consider getting a heater one size larger than recommended.

An additional consideration is whether the pool is an above ground pool heater or inground. Above ground heat pumps would be in the range of 50-75K BTU while inground would be in the 100-150K BTU range.

SunHeater S120U Universal Solar Pool Heater 2 by 20-Feet, Black
  • Simple DIY installation; for in ground or above ground pools
  • Installs on roof, rack, ground or fence
  • Patented web design for maximum exposure to sun's rays


Due to the advancement of technology in swimming pool heaters, you can heat your pool for less cost and better efficiency than ever before. While shopping for a heater, do your research. Ask swimming pool installers and manufacturers questions and read reviews before you invest.

You will also benefit by taking steps to reduce heat loss and increase heat capture. Coupling an electric pool heat pump with a solar system to cover all your bases or add heat loss measures like a solar cover can greatly reduce your maintenance costs, even with a larger upfront investment.

Electric swimming pool water heaters require less maintenance and are more reliable compared to gas heaters. Due to safety requirements for gas heaters, heat pumps have a simpler design and are considered safer.

With its low operating costs, small environmental impact, and ability to maintain consistent water temperatures, electric pool heat pumps are a great long-term investment.

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