How Does a Solar Pool Heater Work?

By Kami Turky


With inflation hitting various industries, finding cost-effective and energy-efficient solutions is becoming essential. And solar pool heaters provide a timely and practical answer to this challenge. 

But how exactly do these systems manage to warm up your pool while keeping costs in check?

They do so by using solar collectors, typically positioned on rooftops or sunny areas. These collectors contain tubes that carry pool water. 

When sunlight hits the collectors, the water inside them absorbs the heat and returns to the pool, gradually increasing its temperature.

In this guide, I’ll walk you step by step through the mechanics of solar pool heaters and how to select the right system for your needs.

Key Takeaways

  • The working mechanism of solar pool heaters uses the sun’s energy, collectors, a filter, pump, valves, and sensors.
  • Before purchasing, evaluating site conditions, considering factors like shading and weather, is essential.
  • Calculating the pool’s volume and surface area determines the system’s type and size.
  • Comparing various systems based on thermal performance and cost aids in making a good choice.
  • Complying with local building codes and standards ensures safety and efficiency in solar pool heating systems.

What Is the Working Mechanism of a Solar Pool Heater?

The working mechanism of a solar pool heater is the process through which pool water gets circulated and heated by the sun’s radiant energy.

At the heart of this lies the solar collector, where water flows to absorb the heat from the sun. 

Picture a solar panel with a tube at both ends, guiding the flow across the panel and through the header/manifold.

Next in line, there’s a filter designed to remove debris before water gets pumped through the collector. 

Following this filtration stage, a pump moves the water through both the filter and collector, subsequently sending it back to the pool, now comfortably warmed.

Also part of the system, a flow control valve, whether automatic or manual, ensures the pool water gets diverted through the solar collector. 

In hot climates, the system can cool the pool by circulating the water through the collector(s) at night.

Some systems also include sensors and a specialized valve to divert water through the collector(s) when the collector’s temperature is enough greater than the pool’s. 

When temperatures are similar, the filtered water simply bypasses the collector(s), returning to the pool without heating.

Solar pool collectors vary in materials, and the type needed depends on your climate and how you intend to utilize the collector. 

Unglazed collector systems, made of heavy-duty rubber or plastic and treated with a UV light inhibitor, are ideal for above-freezing temperatures and are generally more economical.

For colder weather, glazed collector systems come with copper tubing on an aluminum plate, covered with iron-tempered glass. 

These capture solar heat more efficiently and can be utilized throughout the year in various climates. Moreover, glazed collectors have applications in heating domestic hot water.

Both these collector systems, glazed and unglazed, require freeze protection if used in colder areas. 

How to Select Right Solar Pool Heater?

1. Evaluate Your Site’s Solar Resource

Before you buy and install a solar pool heating system, you first need to consider your site’s solar resource. 

Why does this matter? The entire efficiency and design hinge upon how much sun energy your building site can capture.

Consider this. Solar pool heating systems don’t just work with direct sun rays; they also make use of diffuse solar radiation. 

So even if your abode isn’t in a scorching, sun-drenched region, like parts of the southwestern United States, you might not be out of luck. 

If your place doesn’t have a lot of things blocking the sun and it generally faces south, well, it might be a great candidate for solar pool heating.

But how do you know if your site has what it takes? A local solar system supplier or installer should be able to perform an analysis of the site. 

They’ll look into things like shading and orientation, which all affect the sun’s energy reaching the site. This info guides the way for the best positioning of the solar collector.

Now, when you start to really dig into this, you’ll find there’s a whole array of factors that intertwine. 

The direction the collectors should face, how the whole thing should fit into the landscape, the local weather (like those foggy mornings that can really dampen things), and even larger regional climatic considerations all play a part.

These aspects lead to choices on the right type of collector, figuring out the best tilt and orientation, and understanding how different times of the year might affect the efficiency of the system.

What’s more, the solar resource of your site isn’t just about efficiency; it can also impact your wallet. Places with more sun can often get by with a smaller and less costly system while still keeping the pool nice and warm. 

For example, a home situated in the sunny plains of California needs fewer solar panels than a house tucked in the cloudy hills of Scotland. 

In California, a more modest setup might suffice, utilizing solar power to the maximum. 

In Scotland’s less sunny terrain, a more extensive array of panels might be necessary, leading to a higher expense for similar heating.

2. Calculate Your Pool’s Dimensions

Calculating your pool’s dimensions isn’t about measuring the length and width. 

It’s about understanding the entire volume and surface area of the pool to ensure that the heating system can handle its specific requirements. 

The surface area of the pool affects the size of the solar collector required. 

Typically, the collector’s surface area will be between 50% and 100% of the pool’s surface area. In cooler regions, you might need a collector that’s even larger than the pool itself.

This need for larger collectors in cooler regions leads to another critical consideration. If the pool’s surface is larger, naturally, more energy will be needed to heat it, hence requiring a more robust solar heating system. 

The volume of the pool, often calculated by considering its depth, length, and width, plays into how much water needs to be heated. 

A deeper or larger pool will take more energy to raise the temperature, affecting the type and size of the solar system required.

But the size and depth aren’t the only factors here. The pool’s shape might also play a role. 

Unconventional shapes may require special considerations for even heating, guiding the selection of the collector and its orientation. 

Furthermore, the specific location’s characteristics, such as the wind exposure, may need additional considerations. Understanding these aspects could guide you in opting for a specialized heating system or a unique configuration.

For instance, a 15-by-30-foot outdoor swimming pool in Florida might need a collector that equals the pool’s square footage for year-round use, amounting to 450 square feet of collectors. 

In northern California, where systems cover 60%–70% of the pool’s surface area, the story is different since most people use outdoor pools for only 6–8 months.

These geographical variations bring us to the role of the contractor, who will use various tools and software to crunch these numbers, guiding the selection process. 

It’s an intricate dance between science and art, factoring in the pool’s physical dimensions with the climate, desired temperature, and more. 

3. Determine the Collector Orientation & Tilt

The collectors, which can be mounted on roofs or any location near the swimming pool with proper exposure, need to have the correct orientation and tilt toward the sun, as both aspects will influence the system’s performance.

When it comes to collector orientation, the goal is to geographically align the collector to receive the maximum amount of daily and seasonal solar energy. 

Usually, in the northern hemisphere, the optimum direction for a solar collector is true south. 

However, depending on your location and the tilt of the collector, the collector can face up to 45º east or west of true south without a substantial decrease in performance. 

In determining the best orientation, you should also consider roof orientation if the collector will be roof-mounted, the presence of landscape features that could shade the collector at various times, and local weather conditions such as foggy mornings or cloudy afternoons.

Collector tilt is equally essential and varies depending on your geographical latitude and the length of your swimming season, whether it’s just for the summer or all year round. 

Ideally, collectors for summer-only heating should have a tilt angle equal to your latitude minus 10º–15º, while those for year-round heating should be tilted at an angle equivalent to your latitude.

Studies have revealed that even if the collector isn’t tilted at the optimum angle, it doesn’t greatly reduce the system’s efficiency. 

This flexibility means that you can often mount collectors flat on your roof, which may not be at the perfect angle but might appear more visually appealing.

Therefore, in determining the collector orientation, you should collaborate with a skilled contractor to evaluate specific needs and surroundings. This process ensures optimal alignment, balancing energy efficiency with visual appeal.

4. Determine the Efficiency of the System

Determining the efficiency of a solar swimming pool heating system plays a pivotal role as it directly correlates with the overall performance and cost-value of the installation. 

The higher this efficiency rating is, the more solar energy can be harnessed, which, in turn, might lead to cost savings both in the setup and ongoing operation.

For this purpose, you must examine the thermal performance rating of the solar collector. 

This measurement can be expressed in various units, including Btu (British thermal unit) per square foot each day, or kilowatt hours (kWh) per square meter each day. 

You could also convert these ratings into Btu or kWh per day, factoring in the overall collector area. A rating that’s higher signifies more effective collection of solar energy.

Now, it’s important to bear in mind that factors such as local weather conditions, the precision of the instruments used, and other variables can introduce variations in these ratings.

For instance, if two collectors have ratings within 25 Btu/(ft^2day) of each other, these variations might be attributed to external factors rather than actual performance, leading to both units being considered roughly equal in efficiency.

Another aspect worth considering is that solar collectors with higher efficiency not only hold the potential to lower your yearly operating expenses but might also mean that less collector area is needed for the installation. 

This could translate into further cost savings initially.

5. Compare Solar Swimming Pool Heating System Costs

It’s important to compare different solar pool heating systems before you buy one. 

This way, you can figure out how much money you might save by choosing a more efficient type of collector. This might even mean you need fewer panels to heat your pool.

First, get to know how well each collector works by looking at its thermal performance rating. 

You can find this rating on the collector’s specifications or from the manufacturer, represented in terms like Btu (British thermal unit) per day. 

Then, include the total number of collector panels or piping required for the area needed to heat your pool, along with the total installed cost of the system.

Next, you can figure out how much energy you get for each dollar you spend. There’s a formula for this:

Btu per Day per Dollar Spent = Total Installed Cost of System ÷ (Btu/Day×number of Collector Panels/Piping Modules)

Let’s work with an example to make things more clear. Say you have 4 collector panels, each with a rating of 27,900 Btu per day, and the total cost of the system is $3,000.

So, in this case:

3,000 ÷ (27,900×4) = 37.20 Btu per Day per Dollar Spent

But, if you only know the prices and thermal performance ratings of collectors, you can use the following formula:

Btu per Day per Dollar Spent = Btu/Day ÷ Collector Price

For example, if you have a collector with a rating of 21,000 Btu per day and it costs $387, you would calculate:

21,000 ÷ 387 = 54.26 Btu per Day per Dollar Spent

However, don’t make your decision solely on cost or efficiency. 

You should also consider factors such as the design, installation, and the overall suitability of the system for your pool, as they play vital roles in ensuring you get the best solar pool heating system for your needs.​

6. Find out the Building Codes and Permits

Before you take the plunge into installing a solar pool heating system, it’s a must to look into the local building codes and regulations that govern such installations. 

These rules ensure that your chosen system aligns with safety, efficiency, and local standards.

The Solar Rating and Certification Corporation (SRCC) plays an essential role in this process. 

They provide ratings for solar pool heaters under the OG400 standard. This is a guideline that helps consumers identify solar pool heating products that meet specific performance, safety, and efficiency criteria.

By consulting the SRCC’s directory of certified solar pool heaters, you can make sure you’re selecting a product that complies with the established standards. 

Choosing a heater with the OG400 certification means that you’re investing in a system that has been evaluated and approved by experts in the field.

I know navigating these regulations and codes might seem like a daunting task, especially if you’re new to solar heating systems.

This is why I recommend working closely with an experienced installer who understands the local requirements can alleviate some of this burden. 

They’ll handle the compliance with these codes and ensure that the system gets installed correctly, avoiding fines or removal that might occur if the system doesn’t meet the local regulations.

7. Know the Installation and Maintenance You’ll Need

The last thing you want to face when you’re about to dive into your warm, solar-heated pool is a hiccup with the system’s installation or maintenance.

It’s a non-easy task, involving a blend of solar resource assessment, climate consideration, adherence to local building code requirements, and safety protocols.

So, you need to look for a qualified solar thermal systems contractor, one who knows the ropes of installing these systems, can make the whole process less of a plunge into cold water. 

They’ll ensure that the system fits snugly with your location’s unique conditions and legal stipulations.

After the installation, your focus shifts to the system’s maintenance. 

You might think that it’s a full-time job, but with the right care, your solar pool heating system can run smoothly for anywhere from 10 to 20 years. 

Regular checks on the pool’s chemical balance and filtering system can make the collector virtually self-sufficient. 

Glazed collectors might also need some scrubbing in dry climates, but typically, rainwater offers a natural rinse.

And because choosing the right contractor to navigate these waters isn’t as simple as picking a name out of the hat, I’ve gathered some essential questions that could guide you in making this critical choice:

  • “Does your company have experience installing and maintaining solar pool heating systems?” Select a company that’s well-versed in the type of system you desire.
  • “How many years of experience does your company have with solar heating installation and maintenance?” A rich history often equates to quality service; asking for references backs up these claims.
  • “Is your company licensed or certified?” Depending on your state, a valid plumber’s or solar contractor’s license might be more than just a nice-to-have. Check with local authorities, and verify the credentials with your state’s contractor licensing board.


Do Solar Pool Heaters Really Work?

Solar pool heaters really work by using collectors to absorb sunlight and heat pool water, reducing the need for traditional heating methods.

How Long Does It Take to Heat a Pool With Solar Energy?

It takes about 5-6 days to heat the pool with solar energy, with a gradual increase of 2-4 degrees per day. This leads to an overall temperature difference of 12-15 degrees.

How Long Can You Use a Solar Pool Heater?

You can use a solar pool heater for about 10-20 years as long as you properly maintain it and ensure that it’s functioning efficiently throughout its lifespan.


As promised, we’ve covered the ins and outs of solar pool heaters, from their working mechanisms to selecting the right system for your pool’s needs.

And if you ask for my advice, I’d recommend switching all your appliances, where feasible, to solar-powered ones. 

This goes beyond just heating your pool efficiently—it’s about embracing a sustainable lifestyle that benefits both your wallet and the planet.

Do you still have any questions? Feel free to leave them in the comments below.

Kami Turky

Kami is a solar engineer with nearly a decade of experience in researching, testing, and reviewing various solar products. He has also provided technical consultation to several organizations on the best ways to incorporate solar energy into their operations. When he’s not busy helping others find the best solar solutions, Kami enjoys spending time outdoors, hiking, camping, and exploring the natural wonders of his home state.

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