How Does a Pool Heater Work?

Written by Michael Dean
June 5, 2023

pool heaters next to gears

Jumping into a pool of frigid water is not pleasant, so investing in a pool heater is the perfect solution to keeping the water at a comfortable temperature. As a pool owner, you have plenty of options available, from gas to solar heaters, which can be overwhelming.

In this article, I will outline the different types of pool heaters, how they work, the installation process, and how to select the right one for your pool.

Main Takeaways

  • There are three pool heater options available – electrical, gas, or solar.
  • The installation process for a pool heater will depend on the type of heater; make sure to follow the manufacturer’s instructions. If you have any doubts, hire a professional.
  • Before choosing a heater, consider your budget, location, and size of the pool.

How Pool Heaters Work

A pool heater’s job is to keep your water warm. It works by receiving cold water in the heating tank and sending the warmer water back into the pool, keeping the water at a constant temperature with little fluctuations.

Not all heaters work the same way. You can choose from three types of pool heaters: electric, gas, and solar. Each has its own manner of working, how they’re installed, and how they’re maintained.

Electric Heaters

Electric heater diagram above: 1) condenser, 2) compressor, 3) evaporation coil, 4) fan, 5) cool air, 6) warm air.

Electrical heaters work to heat your pool water by transferring warm water directly back into the pool. The pump uses electricity to pull in the outside air (figure 5 in the diagram above) and heat up the water. Inside the pump is a freon, a liquid refrigerant. This freon is compressed (figure 2, via the compressor) until it reaches a high temperature of 200 degrees Fahrenheit. The freon is passed through a valve into a low-pressure system, where it then turns into gas.

This gas circulates through evaporator coils (figure 3) which cools the gas. This cooling of the gas heats the water in the heat pump. The freon, by now, has reverted back to a liquid, and the cycle restarts.

Ideally, the outside temperature should be no less than 50 degrees for optimum heating.

Gas Heaters

Gas pool heater diagram above: 1) heat exchanger, 2) burner, 3) fan, 4) cold pool water entry, 5) heated water exit.

Gas heaters work by burning either natural gas or propane inside a combustion chamber. There are copper coils in the combustion chamber that heat up (heat exchanger, figure 1). The water inside the chamber then runs through the coils, warming up before getting sent back inside the pool (via the heated water exit pipe, figure 5).

Both propane and natural gas burn clean and effectively heat your pool. However, if you’re environmentally conscious, consider using propane, as it has less of an environmental impact than natural gas.

Unlike electrical heaters, gas heaters work independently from the outside temperature, and they heat the water a lot faster.

Solar Heaters

Solar pool heater diagram above: 1) solar panels, 2) temperature sensor, 3) solar controller, 4) pump, 5) filter, 6) check valve, 7) auto valve, 8) heater, 9) salt cell, 10) return, 11) intake.

With the world moving towards more environmentally friendly methods, you are spoilt for choice when going the solar heater route.

Solar Panels

You can choose to have solar panels that heat up the pool water. These panels are installed on the existing pool plumbing. The pool pump filter pumps water through the solar heating panel and back into the pool.

Solar Blankets

As the name implies, a solar cover is a plastic blanket made of “bubbles” that use the sun’s rays to trap the heat in the blanket and warm the pool water below. These solar blankets are great for heating your pool on a sunny day and working hard to prevent evaporation, therefore maintaining your pool’s temperature.

Solar Rings

In theory, solar pool rings are the same as solar blankets. They are made up of two sheets of UV-resistant vinyl. These sheets of vinyl absorb the sunlight and heat the water below. Only 80% of the surface needs to be covered to work. Solar rings are easier to maneuver than solar blankets, as you can attach each section with magnets.

Liquid Pool Cover

A liquid pool cover is an evaporation suppressant. This liquid is poured straight from the bottle into the pool. Doing so creates a barrier between the surface of the water to prevent evaporation, which is the biggest cause of heat loss in water temperature. This liquid can prevent up to 50% of evaporation.

Installation Process

Installing the heater for your pool is a fairly straightforward task if you are a DIY-orientated person. If not, it is advisable to have a professional install it for you.

I have briefly outlined the installation process for each type of heater to give you an idea of what to expect, but always follow the manufacturer’s instructions that you are provided with.

Electric Heaters

Step One: Choose the location

Choose a location to install the heater where it can get a good flow of air, preferably outdoors. There should be no obstructions to the outcoming air. Otherwise, it could end up going back inside the heat pump.

Step Two: Check the water flow rate

Ensure the water flow rate from the pool pump and the filter is high enough for the heat pump. If it’s too low, your water won’t heat fast enough.

Step Three: Mount the base

The base of the electric heater should be placed on a flat surface like concrete or even timber decking. Sometimes, humidity can cause the heater to drip water, so ensure proper drainage below your heater.

Step Four: Do the electrical work

Before installing your pool heater, ensure your circuit breaker can handle the pool pump. Otherwise, it might cause your electricity to trip. Be sure that the cable connecting the heater and electrical point is placed so that people walking over it can’t damage it.

Because the heat pump will need to be correctly installed, it is best to have a qualified electrician do the electrical work.

Step Five: Complete the plumbing

This part of the installation can be tricky, but you shouldn’t have any problems if you follow the manual correctly. As you install the heat pump into existing plumbing, you will need connectors and elbows.

The heat pump requires two pipes only, a flow and return pipe. These are connected to the existing pipes on the pool pump, forcing the water from the pool pump into the heat pump and back through the pool pump into the pool.

Gas Heaters

The steps for installing gas heaters are the same as electric heaters. Choose a suitable location, and connect the flow and return pipes in the existing pool pump using connectors and elbows.

When installing the gas line, you may be required by law to have a professional sign off on it before using it or for them to actually install it for you. Check your local regulations for more information.

Solar Panels

Installing solar panels is a little bit more complicated than the rest. A qualified professional should do it for you. Here is a brief outline of what happens during the installation process.

Step One: Choose your panels

Measure the size of your pool to determine what size panel you will need. You will need panels that are at least 50% of the size of your swimming pool to heat your pool effectively.

Step Two: Choose the location

Choose a location that offers at least 4 hours of direct sunlight and is not obstructed. A good place to put the panels is on your roof. The solar panels don’t need to face the pool or even be near the pool for them to work. They just need to be placed at an angle that faces the sun.

Step Three: Hire a professional

By hiring a professional, they will connect the panels to your existing pool pump effectively, deal with all the plumbing that comes with the solar option, and connect all the wiring safely.

Solar Rings, Blankets, and Liquid Solar Cover

The installation for these is pretty straightforward, and they come with a manual. Generally, the solar rings and blankets are placed on the water surface to float, while the liquid blanket is poured straight from the bottle into the water.

Need to Install a Pool Heater?

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Maintenance Tips

Maintaining your pool heater is the easiest way to ensure it will last for a long time. Here are some helpful maintenance tips.

  • Clean debris from pool pumps
  • Check for leaks or cracks in the pipes
  • Regularly turn the thermostat knob to prevent erosion
  • Keep the area around the heaters clear
  • Check the wiring – there should be no melted or exposed wires

How to Select the Right Heater for Your Pool

Selecting the right pool heater for your pool should be based on your specific needs. You will need to take into account your budget. Sometimes electric heaters are cheaper than solar, or the cost of propane and natural gasses might rise while electricity remains constant.

You would also need to take into account your area and climate. If your area is often cold and overcast, solar heating is not the right option. Electric heaters are more effective in colder climates.

As a general rule of thumb, consider the following three things when choosing a heater:

  • Budget
  • Location
  • Size of pool

Head to my guide on the best electric and gas pool heaters for specific model recommendations. I have a separate article on the best solar heaters if you’re interested in those as well.

Bottom Line

Choosing a pool heater doesn’t have to be complicated; you can choose electric, gas, or solar, and I have outlined the differences and how they work. By considering your budget, the area you live in, and the size of your pool, you can choose the right one for you.

I listed some of my other heater articles below if you need more help.

Questions about how pool heaters work? Let me know.

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