By Audrey HayesUpdated November 2026
Shopping for an open loop solar hot water system usually comes down to one question: will the unit heat water directly enough for your use, and will it fit the way you plan to run it? An open loop system pumps potable or pool water straight through the solar collectors, so there is no heat-transfer fluid between the sun and the water you use. That makes the design simple and efficient, but it also means you need to think about water quality, freeze protection and how the collectors mount. The picks below are judged on the criteria that matter most for this type of system: how directly the collectors fit the intended use, the kit size, the stated specifications, mounting and drainage, and how well the product matches a typical owner’s situation.
Our Top Picks
Our top picks at a glance
- 1
TOP CHOICEBest overallSolar Water Heating System Islander Base Open LoopView on Amazon - 2
Best for above ground poolsDoheny's Solar Heating Systems for Above Ground Swimming Pools (2.5' x 20' Collector Kit)View on Amazon - 3
Best budget pickDoheny's Solar Pool Heating System for Above Ground Pools – Eco-FriendView on Amazon
Quick Comparison
| Product | Best for | Key feature |
|---|---|---|
| Solar Water Heating System Islander Base Open Loop | Owners wanting a general open loop heater with a base-style installation | Open loop design that heats water directly through the collectors |
| Doheny’s Solar Heating Systems for Above Ground Swimming Pools (2.5′ x 20′ Collector Kit) | Smaller above ground pools and tighter installation spaces | Narrower 2.5-foot collector width for compact layouts |
| Doheny’s Solar Pool Heating System for Above Ground Pools – Eco-Friendly – 5′ x 20′ Collector Kit | Owners wanting more collector area on a budget | Wider 5-foot collector width for greater heating capacity |
Solar Water Heating System Islander Base Open Loop
Solar Water Heating System Islander Base Open Loop
Best for: Owners who want a general-purpose open loop solar water heating setup and are comfortable planning the plumbing and mounting themselves.
This is the most flexible choice of the three for owners who are not limited to a single pool shape. It suits anyone who wants to heat water directly for a home or outdoor use, provided the roof or ground mount has good southern exposure and the plumbing can be run with proper valves and drainage.
Key specs
- Open loop configuration, heating water directly in the collectors
- Designed for base-style installation
- Specific collector dimensions and fittings should be confirmed on the listing before purchase
Pros
- Open loop design avoids heat-exchanger losses, which owners often cite as a reason for better daytime efficiency
- Flexible use case beyond a single pool
- Simple layout that is easier to understand for a first build
Cons
- Water quality and freeze protection require careful planning
- Installation details depend heavily on local plumbing and climate
Bottom line: A strong pick for owners who want an open loop system for general heating and are ready to handle the valves, drainage and winterizing themselves.
Doheny’s Solar Heating Systems for Above Ground Swimming Pools (2.5′ x 20′ Collector Kit)
Doheny's Solar Heating Systems for Above Ground Swimming Pools (2.5' x 20' Collector Kit)
Best for: Smaller above ground pools and tight installation spaces where a narrower collector footprint is easier to fit.
This kit suits owners with a modest above ground pool, or those working with limited sun-facing space on a fence line, deck edge or ground rack. Because the collectors are narrower, the layout is easier to position without blocking walkways.
Key specs
- Collector kit size: 2.5 feet by 20 feet
- Intended for above ground swimming pool heating
- Open loop operation, with pool water circulated through the collectors
Pros
- Compact collector width suits smaller footprints
- Designed specifically for above ground pool use
- Straightforward kit format for a pool-focused setup
Cons
- Narrower collectors provide less total heating area than the wider kit
- Still requires a suitable pump and proper plumbing connections
Bottom line: Best for owners with a smaller above ground pool who need a compact footprint and are not aiming for maximum heating output.
Doheny’s Solar Pool Heating System for Above Ground Pools – Eco-Friendly – 5′ x 20′ Collector Kit
Doheny's Solar Pool Heating System for Above Ground Pools – Eco-Friendly – 5' x 20' Collector Kit
Best for: Owners who want more collector area for an above ground pool and a lower-cost entry point into open loop solar heating.
The wider 5-foot collectors give more surface area to catch sunlight, which is useful in cooler climates or for pools where you want a longer swimming season. It fits owners who have a suitable sunny spot and can handle a larger collector layout.
Key specs
- Collector kit size: 5 feet by 20 feet
- Designed for above ground pool heating
- Open loop operation through the collector panels
Pros
- Wider collectors provide more heating area than the narrower kit
- Budget-friendly option within the open loop pool category
- Good match for longer swimming seasons when sun exposure is strong
Cons
- Larger footprint requires more clear, sun-facing space
- Owners often report that heating output depends heavily on weather and pump flow
Bottom line: The best fit for owners with enough sunny space who want more collector area without paying for premium features.
Buying Guide
Confirm Open Loop Compatibility With Your Water Source
An open loop system sends your water through the collectors, so the water source matters. Pool water and potable water need different handling. Potable water passing through copper, PEX or other pipe may need to meet local plumbing codes, and any system that circulates drinking water should be reviewed by a licensed plumber. Check whether the kit is intended for pool use or for domestic hot water before you buy.
Good picks for this: Doheny’s Solar Heating Systems for Above Ground Swimming Pools (2.5′ x 20′ Collector Kit), Doheny’s Solar Pool Heating System for Above Ground Pools – Eco-Friendly – 5′ x 20′ Collector Kit
Collector Size and Heating Area
Collector area is one of the main drivers of heating output. A wider collector provides more surface for sunlight to strike, but it also needs more clear space. Measure the sunny area you actually have before deciding, and remember that shade from trees, fences or neighboring structures can reduce output significantly.
Good picks for this: Doheny’s Solar Pool Heating System for Above Ground Pools – Eco-Friendly – 5′ x 20′ Collector Kit, Solar Water Heating System Islander Base Open Loop
Mounting and Orientation
Collectors generally perform best when they face south in the Northern Hemisphere and are tilted to suit your latitude. Ground racks, roof mounts and base mounts each have different wind loading and access needs. Confirm that the mounting approach works with your structure and local wind requirements before committing to a layout.
Good picks for this: Solar Water Heating System Islander Base Open Loop, Doheny’s Solar Heating Systems for Above Ground Swimming Pools (2.5′ x 20′ Collector Kit)
Freeze Protection and Drainage
Open loop systems are exposed to freezing temperatures in many climates, and water left standing in the collectors can split plastic or damage fittings. Look for a design that drains fully, or plan for manual draindown or a freeze-protection control. If you live where temperatures drop below freezing, this factor can matter more than collector size.
Good picks for this: Solar Water Heating System Islander Base Open Loop, Doheny’s Solar Pool Heating System for Above Ground Pools – Eco-Friendly – 5′ x 20′ Collector Kit
Pump and Flow Requirements
Open loop heating depends on steady water flow through the collectors. Too little flow can overheat the panels, and too much can reduce the temperature rise. Check the flow rate the kit is designed for and match it to a pump you can run reliably. Owners often report that pump sizing is one of the most common setup mistakes.
Good picks for this: Doheny’s Solar Heating Systems for Above Ground Swimming Pools (2.5′ x 20′ Collector Kit), Doheny’s Solar Pool Heating System for Above Ground Pools – Eco-Friendly – 5′ x 20′ Collector Kit
Durability and Materials
Collectors are exposed to UV, heat cycling, hail and debris. Check the stated material and warranty terms. Plastic or polymer collectors are common in pool applications, while metal collectors are more typical for domestic systems. Read the manufacturer’s stated lifespan and UV protection details rather than relying on general claims.
Good picks for this: Solar Water Heating System Islander Base Open Loop, Doheny’s Solar Heating Systems for Above Ground Swimming Pools (2.5′ x 20′ Collector Kit)
Maintenance and Seasonal Care
Open loop systems need periodic inspection for leaks, debris in the collectors and scale or algae buildup. Plan access for cleaning and for shutting the system down for winter. A kit that is easy to inspect and drain will save time over the years, and manufacturers’ maintenance recommendations should be followed closely.
Good picks for this: Doheny’s Solar Pool Heating System for Above Ground Pools – Eco-Friendly – 5′ x 20′ Collector Kit, Doheny’s Solar Heating Systems for Above Ground Swimming Pools (2.5′ x 20′ Collector Kit)
FAQ
What is an open loop solar hot water system?
An open loop system circulates the water you intend to heat directly through the solar collectors. There is no separate heat-transfer fluid or heat exchanger between the sun and the water, which is why open loop designs are common for pools and simple outdoor heating.
Is an open loop system safe for drinking water?
It can be, but it depends on materials, local codes and how the system is installed. Any system that heats potable water should be designed and reviewed by a licensed plumber, and you should confirm that the components are approved for drinking water use in your area.
How much sun does an open loop system need?
Most manufacturers recommend a clear, south-facing location with as little shade as possible during the hours of peak sun. Output drops quickly with shade, so check the site across the full day and across seasons before installing.
Do open loop systems work in cold climates?
They can, but freeze protection is essential. Plan for draindown, a freeze-protection control or seasonal shutdown. Owners in freezing regions often report that winterizing is the most important maintenance step.
Do I need a pump for an open loop solar system?
Usually yes. Open loop systems rely on circulation to move water through the collectors and to keep temperatures even. Pump size should match the flow rate the kit is designed for.
Can I install an open loop system myself?
Many owners handle the mounting and basic plumbing themselves, but any connection to a home water supply or a gas or electric backup should be handled by a licensed professional. Local permit rules may also apply.
Which pick is best for an above ground pool?
Both Doheny’s kits are built for above ground pools. The 2.5-foot kit suits smaller footprints, while the 5-foot kit gives more collector area when you have enough sunny space.
Conclusion
For a general open loop setup that is not limited to one pool, the Solar Water Heating System Islander Base Open Loop is the most flexible choice, provided you are ready to handle plumbing and freeze protection. For an above ground pool with limited space, the 2.5-foot Doheny’s kit offers a compact layout. For more heating area and a lower entry point within the pool category, the 5-foot Doheny’s kit is the better match, as long as you have enough clear, sun-facing space. Match the pick to your site, your water source and your climate before buying.
Sources
- Federal guidance on solar water heating types, design basics and system sizing (energy.gov)
- Research and performance data on solar thermal systems from the National Renewable Energy Laboratory (nrel.gov)
- Plumbing and mechanical code references that apply to water heating and potable water systems
Related reading
- 4 Best Closed Loop Solar Hot Water System Options Compared (2026)
- What Is the Cheapest Solar Hot Water System? Options and Trade-Offs
- Top 5 Solar Thermal Storage Tanks for Home Hot Water Systems
- Top 4 Service Solar Hot Water System Options Compared (2026)
- Sunbird Solar Hot Water System Prices: What You'll Pay and Why It Varies
About Audrey Hayes
Audrey Hayes is part of our editorial team and reviews and edits our solar water heaters guides, checking product details against manufacturer specifications and owner feedback.
