Pool Heater Sizing: What Size of Pool Heater Do I Need?


The right size of pool heaters is crucial in ensuring their optimal functionality. If it is too small for the size of your pool, it will be ineffective in warming the water. On the other hand, if it is too powerful compared to what your pool requires, you will end up unnecessarily wasting energy. 

Curious about the right pool heater sizing? Keep on reading and learn from the things we’ll talk about in this short guide. 

Factors to Consider in Pool Heater Sizing 

What size of pool heater do I need? There is no straightforward way to answer this question. There are certain factors to consider, including those that we will be briefly talking about below. 

  • The Volume of the Pool 

The size of the heater will depend on the volume of the pool. The bigger the pool, the more powerful is the electric pool heater that you will need. There is a specific formula for calculating this depending on the shape of the pool, which will be discussed in the next section of this brief guide. 

  • Ideal Water Temperature 

Individual preferences will also dictate the right size of the pool heater that you will be using. For instance, some would like the water to be just the right level of warmth while others want it to be hot. This will also depend on the place where you live or the season. If it is winter, for instance, you might want the pool to be hotter compared to the temperature of the water during the summer months. 

  • Type of Water Heater 

The technical specifications of pool heaters will vary depending on the type that you will choose. This will also have an impact on the overall heating capacity. Here are some of the pool heater types that you might want to consider. 

  • Gas-Powered Pool Heaters: If power is the most important consideration for you, this is what you should choose. They have high BTU output, which can range from 100,000 to 500,000. If you have a large pool, this is the ideal choice for you. 
  • Electric Heat Pumps: As the name implies, they use electricity instead of gas. It uses ambient air and sunlight to increase the temperature of water in the swimming pool. When in the right environment, it can be cheaper to operate compared to gas, although, it won’t be as powerful. 
  • Solar Pool Heaters: This is the least powerful of the three. It is a popular choice amongst eco-conscious homeowners since it uses renewable energy. It can help you save a lot in the long run because it uses a free source of energy, which is the sun.  
  • Heat Up Time 

Do you want the water in your swimming pool to heat up quickly? If yes, then you might need to find one that will heat within a few minutes after turning it on. On the other hand, if you have the luxury of time, you can choose one that is less powerful if you do not mind waiting a bit before you can take a plunge in a pool with warm or hot water. 

  • Temperature Rise 

This is one of the most important figures that you need to compute to determine proper pool heater sizing. It is the difference between the temperature of the pool water that you want and the current ambient air temperature. When you know the temperature rise, it will be easier to narrow down the choices for pool heaters depending on their heating performance or power. 

  • Heating Efficiency 

The heating efficiency is expressed as BTU, which stands for British Thermal Units. Whether it is in sauna heaters, tent heaters, and other kinds of heaters, the BTU is an important measurement for heater sizing. The higher the BTU, the more powerful is the heater, which also means that it will be more ideal for a larger pool.  

Making the Calculations 

You have to do the math to find the right size of the heater that will work best for your pool.

The first thing that you need to do is to calculate the surface area of the swimming pool. All that you need to do is to multiply the length of the pool with the width. While it may sound so simple, it is a different case when you have an irregular-shaped pool. 

Once you can calculate the surface area of the swimming pool, you have to divide it by three, and this will determine the minimum BTU that is needed for the heater. Take note that this is only the minimum requirement. You can always go higher if you want a more powerful heating capability. 

If there is a freeform pool, the formula can be different. If you go online, you will see different recommendations on how to do the computation. The simplest that we can recommend is to multiply the average length, average depth, and average width with 7, and the answer will be the volume in gallons. 

Read the Label 

You don’t need to make things complicated. The simplest thing that you can do is to read the label or the manual and know the size of your pool. From here, you can have an idea of what size is the best for your needs. Although, this will fail to consider other things, such as the ambient temperature and the temperature rise. 

If you ate unsure about the size to choose, the best thing you can do is to consult with the pros. They know better, so you can be confident that they can offer the right expert opinion. 



Q: What size of pool heater do I need?


The size of pool heater you need will depend on the size of your pool, temperature, and type of water heater, among others. On average, if you have a 1,000-square-foot pool, the recommended heater is 105,000 to 315,000 depending on the intended temperature rise. The table below provides a quick summary of the right pool heater size.  

Temperature Rise  10 Degrees  15 Degrees  20 Degrees  25 Degrees  30 Degrees 
200 square feet  21,000 31,500 42,000 52,500 63,000
300 square feet  31,500 47,300 73,000 78,000 94,500
400 square feet  42,000 63,000 84,000 105,000 126,000
500 square feet  52,500 78,800 105,000 131,000 157,000
600 square feet  63,000 94,500 126,000 157,000 189,000
700 square feet  73,500 110,000 147,000 184,000 220,000
800 square feet  84,000 126,000 168,000 210,000 252,000
900 square feet  94,000 142,000 189,000 236,000 284,000
10000 square feet  105,000 157,000 210,000 263,000 315,000

Q: Can a pool heater be too big?


 No, a pool heater cannot be too big. If it is more powerful compared to what your pool requires, the only thing that can happen is that it will heat water quicker. Nonetheless, there’s no need to worry that there will be short-cycling.

Globo Surf Overview 

At this point, we hope that you already have the answer to this question – what size of pool heater do I need? As noted above, the volume of the pool and ambient temperature, among other factors, will have an impact on the right side of the pool heater. Make sure to consider all relevant factors to keep your pool safe and comfortable as water is heated.

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My name is David Hamburg. I am an avid water sports fan who enjoys paddle boarding, surfing, scuba diving, and kite surfing. Anything with a board or chance I can get in the water I love! I am such a big fan I decided to start this website to review all my favorite products and some others. Hope you enjoy!