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Pool Heater vs Heat Pump: What’s the Difference?

Last Updated: February 21, 2020

A Pool Heater

The two primary methods of heating pools are with pool heaters and heat pumps. At first glance, it may be unclear what the difference between these two methods is, and which one would be superior for your situation. This guide explains the differences between the two and walks you through the things you need to understand to choose the machine which is right for your pool.

How does a pool heater work?

A pool heater

A pool heater. Here we see the Hayward W3H400FDP

Pool heaters are added to your system between your pump and your pool. After the water has been cleaned, it is pressurized by the pump for the return trip to your pool, and then goes through the heater, which uses natural gas, propane, or electricity to heat the water.

The heating process works like a burner on a stove. The natural gas or propane is burned to heat a metal element, or the electricity is run through that element, causing it to heat up. The water is run over the heating element, taking the heat with it as it goes.

For most people, pool heaters powered by natural gas will be the cheapest option and can cost as little as three dollars per hour to heat your pool. Propane is more expensive, and you’ll either need a line from the city or a large, underground storage tank to run the heater for extended periods. At the high side, propane pool heaters can cost nine dollars per hour, though they’re often much less than that.

The cost of running an electric pool heater varies. The most important factor is the cost of electricity in your area, though in most places gas and propane will still be cheaper.

Pool Heater Pros

The best thing about pool heaters is that they tend to be cheaper to purchase and install than heat pumps. Like many pool accessories, they’re not the cheapest items in the world, but you can save hundreds and sometimes thousands of dollars by buying a pool heater instead of a heat pump.

Since pool heaters operate by heating something to a very high temperature and then using that to heat the water, they’re the faster of the two heater types, and the race isn’t even close. Pool heaters can usually heat a pool in just a few hours, and while heat pumps can eventually reach the same temperatures, it may take them a day or two to get there, especially if you own a large pool.

Unlike heat pumps, pool heaters work well in any temperature. They’re creating their own heat, so they don’t get less efficient as the weather gets colder. However, it’s worth noting that both types take longer to heat the pool then the temperature drops.

While this varies from model-to-model, pool heaters are typically easier to install. There’s a good chance that the area where your pump is located already has a gas line or electric outlet nearby that you can use for your pool heater.

Pool Heater Cons

The biggest downside to pool heaters is that they tend to cost far more to run. While it varies from model-to-model, you can expect your pool heater to cost between five and fifteen times as much to run as a heat pump on an hourly basis. That’s not a lot in absolute terms, as you may recall, it’s between three and nine dollars an hour. However, it’s still worth pointing out that heat pumps cost much more in relative terms.

The other major downside relates to maintenance. The most important part of your pool heater is also the part that is most likely to break. The heat exchanger, the part that transfers the heat to the water, is exposed to two serious situations that are the death of most man-made materials. They’re required to run at high temperatures, which damages them at a molecular level, and they have water running over them all the time.

Water is abrasive, and it and the constant heat cause the heat exchanger to typically wear out before other parts in the pool heater. Unfortunately, it’s the most expensive part to replace. In some cases, it will be better to buy a brand-new pool heater than to pay just as much to replace the heat exchanger.

How does a heat pump work?

Pool Heat Pump

Here we see the HeatPro heat pump 

Heat pumps work like your air conditioner or refrigerator but in reverse. They rely on a fundamental law of gasses. When you compress them, they get hotter. The more you compress them, the hotter they get.

So, a heat pump starts by taking in ambient air. It runs the warm air over an evaporator, which is used to heat a refrigerant. It’s confusingly-named, but essentially a refrigerant is a substance used to transfer heat in or out of something. After the refrigerant is heated by the ambient air, the heat pump compresses it to make it much hotter and then runs it through a heat exchanger to transfer that heat to the water.

This does warm the water, but the effect isn’t as dramatic as is it with a pool heater since the temperatures involved are much lower.

The heat transfer cools the refrigerant, and the machine returns it back to the start of the cycle to be heated again by the air. Technically, there are a few more steps in the process that we didn’t cover here, but you should now understand in broad strokes how heat pumps work.

Heat Pump Pros

Heat pumps are very energy efficient. They cost about one-fifth of what the cheapest pool heaters cost to run on an hourly basis, and that’s at the least generous. Relative to less efficient pool heaters, they’re 93 percent more efficient, from a cost perspective. If you can afford to spend the upfront cost required to buy a heat pump over a pool heater, it’s an investment that could very rapidly pay for itself and will pay for itself faster the more you use it.

When it comes to actual energy transfer, heat pumps can achieve 500 to 600 percent efficiency, relative to the 82 to 94 percent on a gas, propane, or electric heater. This is possible since they’re taking advance of the energy available in the warm, ambient air to jumpstart the heating process. That’s a big part of why they’re so inexpensive to operate.

That makes them the superior choice for people who will use their pools nearly every day. It takes a while for these machines to heat your pool, but once it’s heated, it can stay that way nearly indefinitely at a low cost, so it makes sense to use it as much as possible.

Heat Pump Cons

A large downside to heat pumps is how slow they are. While pool heaters could warm a pool in just a few hours, it may take a pool heater a day or two to get your pool warm. If your plan is to use your pool for a few hours on a few colder weekends during the year, you’re not going to be getting great value out of your heat pump, since they tend to hundreds or thousands of dollars more expensive than pool heaters.

The biggest downside is that there’s a temperature at which your heat pump stops working. As you may recall from the section on how heat pumps work, the process starts by using warm air to heat a refrigerant. If the air isn’t warm enough, then the heat pump won’t function properly, and won’t heat your pool.

The cutoff temperature is about 50 degrees Fahrenheit. That makes the heat pump a bad choice for places where the temperature quickly gets below 50 degrees in the Fall, and if it doesn’t get above that temperature for a few days at a time, you won’t be able to use your heat pump all winter.

Which heater is right for your pool?

Which model is right for you depends primarily on how you plan to use your pool. If you’d like to swim multiple days a week and add a few weeks or months per year in the fall and spring in which you can swim, then the heat pump is probably the superior choice for you. In some climates, you’ll be able to use the heat pump to heat your pool year-round, and in others, you won’t add too much time because the temperatures will drop below 50 degrees too quickly.

On the other hand, if you want to swim every now and then, and want the option of swimming in the deep winter, then the pool heater is probably the device for you. It heats more quickly, though it costs more to run. However, it’s cheaper to install, and not dependent on the weather, making it a more versatile choice.

We hope that our guide has cleared up the major differences between pool heaters and heat pumps and has led you to the variety of pool warmer that is right for you.