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Pool Heater Size Chart For Choosing The Right Heater

Having your open personal pool in your backyard is definitely one of the best luxuries, especially in summer when you can enjoy a nice swim in the warm water whenever you want. However, owning a pool also comes with a lot of other responsibilities which include timely maintenance of the pool as well as making sure it is equipped with all the necessary equipment according to the season. You will find it really helpful when winter comes around and it becomes nearly impossible to step into the water without a proper pool heater.

Therefore, a lot of pool owners tend to buy a permanent water heater for their pool which can be enabled/disabled as per the user’s requirements. In most cases, the pool heaters are installed just before the entry point of the water so that there is always warm water in circulation, maintaining a certain temperature for the entire pool. If you are also looking for a pool heater, you will find a guide for the right pool heater size very helpful.

But before we discuss the appropriate size of the pool heater for your pool, let us first understand talk about pool heaters in general and try to understand how these units function to keep such a large water body at a constant temperature.

What is a Pool Heater?

A pool heater is a device or a rather intricate system that includes multiple components that are used to raise and maintain the temperature of water in a swimming pool. While the pool heaters are mainly designed for swimming pools, they are also frequently used for spas, even large hot tubs. It operates by using various methods to generate heat and then transferring that heat to the pool water. This helps to extend the swimming season by allowing people to swim comfortably even when the outside temperature is lower than usual.

There are multiple different types of pool heaters available on the market. But, regardless of the type of pool heater you are getting, you will find that the basic working principle of all pool heaters is pretty much the same. They all work by transferring heat to the water using a heat exchanger. A heat exchanger is a device that allows heat to be transferred from one medium to another medium without direct contact.

A pool heater is a great investment for anyone who wants to enjoy pools in a rather colder season and to make their pool more comfortable and relaxing than ever. But to get the best It’s important to consider various different factors of the pool heater such as the size of your pool, the capacity of the heater, and the average temperature of your region so you can find the right one to meet your needs. First, let us talk about the different types of pool heaters available out there.

Different Types of Pool Heaters

Just like most other accessories that are designed for a pool, there are a couple of different types of options available on the market for a pool heater. While the core functionality of the heater remains the same, you will find that these options differ a lot when it comes to the power source, performance, and capacity. Therefore, you should always check which type of pool heater is the right fit for your pool before you start looking at available options. Mainly, pool heaters are divided into 3 categories that are gas pool heaters, electric heat pumps, and solar pool heaters.

1. Gas Pool Heater

Gas pool heaters can be considered one of the most reliable options for a pool heater since you can use these heaters whenever you want. Gas pool heaters use either natural gas or propane to power the system, which further charges the heat exchanger and other components to heat up the water. The gas is burned in a combustion chamber, which heats up the water in a heat exchanger. Gas pool heaters are best suited for larger pools as they can increase the water temperature at a much faster rate.

One of the main benefits of a gas pool heater is that they are relatively cheaper and also very easy to operate. They are also very efficient and can heat the water quickly, even amidst a strong winter. However, gas pool heaters require a gas line to be installed, which can be pretty expensive. Also, you have to consider the running costs of the pool heater which add up to the fuel cost. Also, you will notice that gas pool heaters require more frequent maintenance and care compared to other options.

2. Electric Heat Pump

Just like most other accessories on the market, pool heaters also have an electric alternative option available. Electric pool heaters also work in a similar fashion as other types of pool heaters. Except, these heaters can utilize electricity as the main power source or the heat exchanger. Electric heat pumps operate by using electrical resistance to generate heat, which is then transferred to the water body. Electric pool heaters are relatively easy to install and are best suited for smaller pools or spas. They can also be used to supplement the heating of larger pools.

Electric pool heaters are also quite cheap. And depending upon the size you are choosing, you may also find it rather affordable to operate an electric pool heater in terms of energy bills. However, they can be costly to operate in the long run due to the high cost of electricity, especially for large water bodies. Additionally, electric pool heaters are not as fast as other heaters and can take a long time to heat the water, especially in a cooler climate.

3. Pool Solar Heater

Solar heaters are the latest addition to the pool heater categories, and it is quick;y gaining a lot of popularity with their eco-friendly design and performance. Solar pool heaters use solar energy to heat the water in the pool. This is done using a series of solar panels, which are typically installed on a roof or a nearby structure. So, it could be the best option for you if you already have a solar energy setup installed in your home. In a solar pool heater, the water is circulated through the solar collectors, where it is heated by the solar energy, before being returned to the pool.

One of the key aspects where solar pool heaters are very valuable is that they are completely environmentally friendly and can be very cost-effective in the long run. They don’t require any additional fuel or electricity to operate, so once they are installed, they can be used for free. Additionally, solar pool heaters are very efficient in warm and sunny climates.

However, there are also a few drawbacks to solar pool heaters. For instance, they require a significant initial investment which can be a bit much, especially if you don’t already have a solar energy setup in your home. They also require a lot of roof space or an alternative location to install the panels. Lastly, they may not be as effective in cooler climates or cloudy seasons where there is not enough sunlight to warm up the water.

Factors That Affect Pool Heater Size

Apart from the type of pool heater you are choosing, there are a few more factors that you need to consider when you are making a choice to be able to choose the right pool heater for your pool. These factors include pool size, required water temperature, climate conditions, general pool occupancy, etc. So, you need to know about these factors and keep all of these options into consideration before you decide what size of pool heater is perfect for you.

1. Pool Size

The size of your pool is one of the most critical factors to consider when selecting a pool heater. The larger the pool, the larger the heater you’ll need to effectively maintain the water temperature. Pool heaters are typically represented in BTUs (British Thermal Units), which measure the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. As a general rule of thumb, you’ll need a heater with a capacity of 50 BTUs per square foot of pool surface area, and so on. So, it is quite easy to find out the appropriate BTU rating for your pool based on the mass of water.

2. Required Water Temperature

The desired water temperature that you would want in your pool is also important to note before you start looking for a pool heater. If you want to maintain a temperature of, say 80°F, you’ll need a larger heater than if you want to maintain a temperature of 70°F. To put it simply, the higher the temperature, the more BTU capacity is needed on the pool heater to make it possible.

3. Climate Conditions

One of the main reasons to get a pool heater in the first place is to keep the water temperature higher than the surrounding temperature. Therefore, the climate and average temperature in your area are other factors to consider when you are selecting a pool heater. If you live in a cooler climate, you’ll need a larger heater to compensate for heat loss due to lower air temperatures. On the other hand, a smaller heater may be sufficient to maintain a comfortable water temperature if you live in a warmer climate.

4. Pool Occupancy

Another notable factor that can affect the capacity of the pool heater is pool occupancy. It includes the average number of pool users as well as the roundabout of how long the pool is going to be used every day. If you plan to use your pool frequently, you’ll need a larger heater to maintain a comfortable water temperature for longer periods of time. If you only plan to use your pool occasionally such as on weekends, a smaller heater may be sufficient for your needs.

5. Heater Efficiency

Last but not the least, you should check the efficiency of the pool heater as it also plays an important role in the performance of the heater. More efficient heaters will require less energy to produce the same amount of heat, thus saving you money on energy costs and running costs in the long run. However, more efficient heaters can also be more expensive to purchase initially. Also, you will need to carefully check out all available options under your budget and check out the reviews of each option to find the most efficient option for your needs.

How To Calculate The Size of a Pool Heater?

Now comes the most important part, how can you actually find out the right capacity which will not only be compatible with your pool but also makes it a feasible choice for the future? To put it simply, you will have to compare the pool parameters and apply a little bit of calculation to get the approximate size of the pool heater that will be perfect for you. Here’s how you can easily calculate the pool heater’s size.

1. Determine the Surface Area of your Pool.

Before you can get an idea about the appropriate capacity of the pool heater suitable for your pool, you should first find out the surface area of your pool. This will give you an idea about the volume of the water body that is supposed to be heated by the pool heater. You can determine the surface area of your pool by multiplying the length by the width. And even if you don’t have an exactly square or rectangular pool, just create an approximate rectangular boundary around the pool’s edges and use its surface area for calculations.

2. Determine the Desired Temperature Rise.

The desired temperature rise, which is expected from a pool heater, is the difference between the average air temperature in your region and the desired water temperature that you want in your pool. For example, if the average air temperature is 60°F and you want your pool water temperature to be 80°F, the desired temperature rise would be 20°F.

3. Determine the heat loss.

Heat losses occur when heat escapes from the pool water into the surrounding air. Heat loss depends on several factors, such as air temperature, wind speed, humidity, and the type of pool cover. While it is not possible to calculate the exact amount of heat loss in all cases, you can simply go with general consideration and put it into your equation for good measure. A good estimate of heat loss is around 10 BTUs per hour for every square foot surface area of the water for every single degree Fahrenheit water temperature difference.

4. Calculate the required BTUs.

Now comes the last step, calculating the approximate BTU rating you want on your pool heater.

To calculate the required BTUs, you can use the following formula and put the values we have considered.

(Approximate BTU output) = Pool Surface Area x Required Temperature Rise x Heat Loss Factor

For example, if you have a 100-square-foot pool, and you want to raise the temperature by 30°F, and the heat loss factor is 8, the required BTUs rating would be:

(BTU output) = 100 x 30 x 8 = 24,000 BTUs

So in this example, you would need a pool heater with a BTU output of 24,000 to effectively heat the pool water. And just to be safe, we will suggest rounding it up to 30,000 to make an efficient choice in case of sudden temperature drops.

Pool Heater Size Chart

Now that you know the BTU rating of the pool heater size and how you can check out the appropriate BTU rating for your pool, let us compare a few standard options available on the market based on approximate pool sizes and water volume. If you find the pool size or water volume close to any of the ones mentioned here, you can easily go with the respective BTU rating mentioned on the table or your pool heater without any problem.

Approximate Pool Size


Water Volume


Required BTU Rating

(Gas Pool Heater)

Required BTU Rating

(Electric Pool Heater)

12 x 24 12,960 49,058 100,000 – 150,000
14 x 28 17,640 66,774 150,000 – 200,000
16 x 32 23,040 87,215 200,000 – 250,000
18 x 36 29,160 110,382 250,000 – 300,000
20 x 40 36,000 136,274 300,000 – 400,000
Round/Circular Pools
15 Round 7,950 30,094 100,000
18 Round 9,050 34,257 100,000
21 Round 15,580 58,976 100,000 – 150,000
21 Round 15,580 58,976 100,000 – 150,000

Why Should You Choose The Right Size of a Pool Heater?

While it may not seem important, choosing the right pool heater size for your pool is a very intricate part of the process. As the size of the pool heater affects the performance as well as the experience of the user, it is essential to choose the right size of pool heater for your pool. Otherwise, you might end up with an expensive pool heater which is not much of a use when winter is at its peak. A pool heater that is too small for your pool will struggle to maintain the desired temperature, which means it will need to run longer and consume more energy to keep the water warm. A smaller heater may also be unable to maintain a comfortable water temperature, affecting your swimming experience.


So far, we have gone through the basic working principle of a pool heater, different types of options available on the market, the importance of choosing the right pool heater size, and many other essential aspects you should know about before you can buy a pool heater. So after reading our guide, it is safe to say that you are now equipped with everything you need to know and you can now easily go with the best option for your needs based on the information provided here. If you have any doubts regarding any topics covered in our guide today, you can reach us via the comment section below.

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