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How to Choose the Right Pool Heater and Determine the Perfect Size for Your Pool?

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Categories: Q&A Topics, Energy Efficiency, Heaters
 
As the seasons change and the chill of winter approaches, many pool owners begin to ponder the same question: "What size pool heater do I need?" The answer lies in finding the perfect pool heater. But choosing the right pool heater and determining the correct size for your pool is not as simple as it may seem.
 
It requires a careful understanding of your pool's unique characteristics, your climate, and your heating preferences. In this comprehensive guide, we'll explore how to choose the right pool heater and what size heater your pool needs, ensuring you enjoy a warm and inviting pool all year round.
 
Understanding the Types of Pool Heaters
Before diving into the specifics of choosing the right pool or spa heater, it's essential to understand the different types of pool heaters available on the market. Each type has its unique features, benefits, and considerations.
 
Gas Heaters
When it comes down to it, there are only a couple ways to heat water... The most common method is using a gas heater. These heaters will burn natural or propane gas to heat the water. There are also heat pumps that essentially work like a backward air conditioner. Heat pumps use condensed refrigerant that heat up as it is condensed. It will use the heat from the condensing refrigerant to heat the water. Lastly, there are all electric heaters. These have an element that heats up using high-voltage electricity. The water passes over the element, heating the water.
 
Gas heaters are the most popular option when it comes to heating water because they are the most versatile and most powerful. The only major consideration when it comes to gas heaters is elevation. If you are in higher altitude areas, you’ll need to consider your elevation when purchasing a heater. There are some heaters that will work from sea level all the way up to 9,000 feet without any issues. While others will require a specific heater depending on your elevation. There are two main types of gas with these heaters: natural gas and propane. When choosing the type of gas for your system, verify if you’re going to need a propane tank or if you can run a natural gas line to your heater from the source. If there are any questions about gas, your local gas provider is your best point of contact. Some heaters can be easily converted from natural gas to propane and vice versa, some cannot. We would be happy to review different options with you.
 
Heat Pumps
A heat pump is a great way to heat a pool with low energy costs. This option uses electricity, but not nearly as much as an all-electric heater. The primary downfall when it comes to heat pumps is that they’re not very powerful, so the option is limited based on the size of your pool. Using a heat pump in the right conditions is by far the least expensive way to heat water. Not the fastest, but the most efficient.
 
A heat pump is a great way to maintain a temperature at low costs during warmer months. Gas heaters and electric heaters are not greatly affected by outside air or water temperature, but heat pumps are. Heat pumps work best in warm or humid climates for that reason, Floridians LOVE heat pumps!
 
Electric Resistance Heaters
Electric heaters are different from heat pumps as they use electricity to heat an element that heats the water as it passes through. These use a lot of current and voltage to heat the water and are typically used on smaller bodies of water, like spas and small above-ground pools. Some of these heaters come salt compatible.
 
These heaters use electric currents to generate heat and are suitable for small pools or spas. They are less common due to their higher energy consumption.
 
Understanding Key Features of Pool Heaters
When selecting the right pool heater, understanding specific features and terminologies can guide you to the perfect choice. Let's delve into some essential aspects:
 
Low NOx Emission
NOx (or oxides of nitrogen) is an emission produced during combustion. Low NOx indicates limited emissions, essential in regions with strict emission regulations, such as Texas, Utah, and some Southern California counties. Brands like Raypak offer some Low NOx models, while others like Pentair make all their heaters Low NOx compliant.
 
ASME Certification
For commercial properties, heaters must pass ASME (American Society of Mechanical Engineers) tests to ensure suitability. ASME-certified heaters typically feature a robust heat exchanger and glass-lined metal headers, meeting the rigorous demands of commercial applications.
 
Cupro-Nickel Heat Exchangers
Cupro-Nickel heat exchangers are copper exchangers nickel-plated for resistance against abrasion, making them ideal for salt pools or pools with harsh water. Investing in a Cupro-Nickel heater ensures durability and compliance with warranty requirements.
 
Automation Compatibility
Modern heaters offer compatibility with automation systems, allowing temperature control through the automation interface. The functionality may vary based on the heater, pool setup, and automation system, but the convenience of remote temperature setting is a significant advantage.
 
Millivolt Standing Pilot (Obsolete Technology)
Older heaters used a standing pilot, a constant flame that ignited the gas running through the burners. This technology is now obsolete due to challenges in windy conditions and potential safety risks. Modern heaters use electronic ignition, similar to gas stoves, providing a safer and more efficient operation.
 
Above Ground Pools and Spas: Special Considerations
 
Above Ground Pools
When shopping for heaters for your above-ground pool, the largest obstacle that you may face is the type of plumbing that is used. Most above-ground pools utilize a flex hose type of plumbing, which many heaters are not compatible with. It's crucial to ensure that your plumbing is compatible with your preferred heater when looking to add a heater to your above-ground pool system.
 
Spas
For spas, the primary consideration is the capacity of the heater. Spa heaters are typically oversized to heat the spa quickly within a reasonable timeframe. For example, a large spa that holds 1,000 - 2,000 gallons can perform well with a 125,000 BTU-rated heater, resulting in a 45-minute to 1.5-hour heat-up time, depending on your location. If you increase the BTU rating to 250,000 – 350,000 BTU, the heat-up time can drop to as little as 20-30 minutes. Choose the capacity of your heater according to your preferred heat-up time.
 
What Size Pool Heater Does My Pool Need?
Choosing the right-sized heater for your pool is a critical decision that impacts both comfort and energy efficiency. Whether you're looking to extend your swimming season or maintain a specific minimum water temperature, selecting the appropriate heater size is essential.
 
Different pools have unique requirements, and understanding how to determine the correct heater size for your particular needs is vital. From calculating the volume of your pool to considering the desired temperature increase, various factors play a role in this decision. In this guide, we'll explore the traditional methods to calculate the right pool heater size and introduce a handy pool heater sizing calculator to simplify the process.
 
Pool Usage Patterns and Heating
Preferences Pool owners have diverse preferences when it comes to using their pools, especially during the cooler months. Some individuals like to maintain a consistent minimum water temperature, necessitating regular heater usage, similar to how a home thermostat functions. In contrast, others might only heat their pools for specific occasions or use them less frequently during colder periods. Recognizing these varied usage patterns is crucial when determining the ideal heater size for your pool.
 
At this point, you might be asking yourself, “What size pool heater do I need?” No matter your usage preferences, there are four basic steps to take in order to determine heating requirements for your pool.
 
  1. Calculate the volume of your pool in gallons. You probably already have this information, but we can use a simple example to illustrate the process:
     
    Volume (in gallons) = Length (ft.) x Width (ft.) x Average depth x 7.5
     
    In the case of a rectangular pool that measures 20' by 30' with a shallow-end depth of 4' and deep-end depth of 8', the calculation is this:
     
    Volume = 20 x 30 x 6 x 7.5 = 27,000 gallons
     
    This information is important because water volume dictates how many BTUs will be needed for a specific pool. BTUs are a measurement that represents the heat necessary to raise one pound of water one degree Fahrenheit). Heaters, as you've probably noticed, are identified partly by their BTU capacity per hour.
     
     

  2. Determine how many BTUs will be needed to raise the temperature throughout the pool one degree Fahrenheit. As we said BTUs are based on pounds, and one gallon of water weighs 8.34 pounds, so the pool from the example above has 225,180 pounds of water.
     
    27,000 gallons x 8.34 = 225,180 pounds of water

  3. Find out how many BTUs are required to achieve a one-degree temperature change within a 24-hour period. To do this you'll divide the pool volume in pounds by 24.
     
    225,180 / 24 = 9,382

  4. Now that you know how much heat is required to achieve one degree of temperature change over 24 hours you can use that as a multiplier, along with the number of degrees of desired temperature increase, to determine how many BTUs are necessary for your pool to reach the intended temperature in the 24-hour time frame.
     
    For instance, if we want to raise our example pool's water temperature from 65*F to 85*F in 24 hours:
     
    9.382 x 20 degrees = 187,680 BTUs will be needed, or 187K as commonly notated
That temperature must be maintained, of course, but this can ordinarily be done with no more energy required than that used in the initial warmup phase. Once you have a solid idea of how long it will take to heat your own pool (based on its size and the capacity of available heating options), you're better equipped to make an informed decision.
 
Gas Line Sizing: A Critical Consideration
When selecting the right heater for your pool, one often overlooked but vital aspect is the proper sizing of the gas line. The distance the gas line runs and the size of the heater in BTU must be carefully matched to ensure optimal functionality. Incorrect sizing can lead to the heater not functioning properly or not working at all.
 
Here's a handy pool heater sizing chart to help you size your heater based on the length and size of the gas line:
 
Natural Gas Through Iron Pipe:
Distance in Feet
100-150k BTU
200k BTU
250k BTU
300k BTU
350k BTU 400k BTU
500k BTU
0 - 50
0.75"
1"
1"
1.25"
1.25"
1.25"
1.25"
50 - 100
1"
1"
1.25"
1.25"
1.25"
1.25"
1.5"
100 - 200
1.25"
1.25"
1.25"
1.5"
1.5"
1.5"
2"
200 - 300
1.25" 1.25"
1.5"
2" 2"
2"
2"
 
Liquid Propane Gas Through Iron Pipe: 
Distance in Feet
100-150k BTU
200k BTU
250k BTU
300k BTU
350k BTU 400k BTU
500k BTU
0 - 50
0.75"
0.75"
1"
1"
1"
1"
1"
50 - 100
0.75"
1"
1"
1"
1.25"
1.25"
1.25"
100 - 200
1"
1"
1.25"
1.25"
1.25"
1.25"
1.25"
200 - 300
1" 1.25"
1.25"
1.25" 1.25"
1.5"
1.5"
 
No matter which heating method makes sense for you, it's essential to consider your heating purchase as an investment.
 
Utilize a Pool Heater Sizing Calculator
For those looking to find the perfect size for their pool heater or heat pump, you can utilize this pool heater sizing calculator. This handy tool simplifies the process by taking into account various factors such as pool size, location, and desired temperature. By using this calculator, you can ensure that you choose the right heater size for optimal performance and energy efficiency. It's a valuable resource that takes the guesswork out of the equation, providing you with accurate and tailored recommendations.
 
Comparing Popular Heating Options
When it comes to pool heater sizing, it's essential to understand the difference between a pool heater and a pool heat pump. A pool heater typically refers to a gas heater that burns fuel to generate heat. A heat pump, on the other hand, uses electricity to capture heat from the ambient air and transfer it to the pool. Proper pool heat pump sizing is crucial to ensure that the heat pump operates efficiently and meets the heating demands of your pool.
 
 
 
 
Pros  - Nearly 50% cheaper than comparable heat pump
- Heats pool quicker - gas heaters burn either propane or natural gas inside a chamber that gets hotter faster
- Fairly simple to install
- Works better in cold climates
- Much lower energy bills - only uses electricity
- More energy efficient
- Similar in operation to a home HVAC unit
- Longer life span (usually 10 years) due to the less volatile nature of the heat pump's internal processes (they draw heat from the air rather than creating it internally)
- Safer operation than gas heaters  
Cons  - More costly to operate - costs are tied to rising gas prices
- Less energy efficient - as much as 20% of the source gas doesn't burn completely
- The exhaust created by the burning process is harmful to the environment 
- More likely to need repair - equipment failure is typically an issue sooner than with heat pumps
- Shorter life span (usually 5 years) 
- More expensive - heat pumps are more complex than gas heaters, which helps explain the higher price tag
- Slower heat-up - heat pumps draw outside (often very cold) air, then compresses it into gas which heats the circulating water
- Trouble with very cold climates 
 
When it comes down to it, the gas heater (as the comparative BTUs suggest) will finish the job faster, and at less cost up front, but the heat pump is a more long-term approach, more likely to provide years of reliable service.
 
No matter which route makes more sense for you, It pays to treat your heating purchase as an investment. You will find that the jump in price from one size to the next (in both heaters and heat pumps) is not substantial in a relative sense.
 
Going up a level or two in capacity from the minimum baseline you determined earlier won't greatly increase your energy consumption, either. A larger model, also, will require less time to perform the same amount of heating and thus be subject to less use.
 
Enjoy a Warm Pool All Year Round
Choosing the right pool heater and determining the perfect size for your pool is an investment in comfort and enjoyment. By understanding the types of heaters, considering essential factors, and following our guidelines, you can extend your swimming season and relish the luxury of a warm pool even in the chilliest months.
 
It's important to remember that using additional methods to keep the pool warm (solar covers, solar panels, etc.) is another key way to place less strain on the heater itself, which can add years to its usefulness and provide a consistently comfortable pool. Check out one of our previous posts about additional heating methods for your pool.
 
Need personalized assistance? Contact us today. Our expert team at Pool Supply Unlimited is here to guide you every step of the way. Explore our extensive range of pool heaters and pool supplies to make your pool closing process as smooth as a summer swim. Shop Pool Supply Unlimited today!
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