By Audrey HayesUpdated November 2026
Looking for a closed loop solar hot water system but not sure which model fits your roof, climate and tank setup? A closed loop system circulates a glycol-water antifreeze mix through the collector and a heat exchanger, so the potable water in your home never passes through the panels. That makes it a practical choice for freezing winters and hard water areas. The picks below were selected by comparing published specifications, brand reputation and the patterns owners commonly report about freeze protection, tank coil design, collector construction and ease of installation. Each choice is matched to a specific need so you can narrow the list quickly.
Our top picks at a glance
- 1
TOP CHOICEBest overallSolar Water Heating System Skyline5 Closed LoopView on Amazon - 2
Best for large households1000 Liter Water Heater Active Split System Single Coil Tank 45 Deg FrView on Amazon - 3Best for small homes and cabins400 Liter Water Heater Active Split System Dual Coil Tank 45 Deg FrameView on Amazon
- 4
Best for pool heatingDoheny's Solar Pool Heating System for Above Ground Pools – Eco-FriendView on Amazon
Our Top Picks
Quick Comparison
| Product | Best for | Key feature |
|---|---|---|
| Solar Water Heating System Skyline5 Closed Loop | Most homeowners wanting a complete closed loop package | Closed loop design for freeze protection |
| 1000 Liter Active Split System Single Coil Tank | Large households with high daily hot water use | 1000 liter capacity with single coil heat exchanger |
| 400 Liter Active Split System Dual Coil Tank | Small homes, cabins and limited mechanical rooms | Dual coil tank for solar plus auxiliary heating |
| Doheny’s Solar Pool Heating System | Above ground pool owners | Compact 5′ x 10′ space saver collector |
Solar Water Heating System Skyline5 Closed Loop
Solar Water Heating System Skyline5 Closed Loop
Best for: Homeowners who want a complete closed loop package with freeze protection built into the design
This suits homeowners in climates with regular freezing who want a system that does not rely on draining or on the water in the collector. It also fits builders who prefer a matched collector and tank package over sourcing parts separately.
Key specs
- Closed loop glycol circulation between collector and heat exchanger
- Designed for residential domestic hot water
Pros
- Freeze protection through the antifreeze loop
- Potable water stays separate from the collector
- Single-source package simplifies planning
Cons
- Glycol requires periodic checks of concentration and pressure
- Installation still requires plumbing and electrical work
Bottom line: A strong first choice for most homeowners who want a closed loop system without assembling every component themselves.
1000 Liter Water Heater Active Split System Single Coil Tank 45 Deg Frame Evacuated Vacuum Tubes Hot SRCC Certified
1000 Liter Water Heater Active Split System Single Coil Tank 45 Deg Frame Evacuated Vacuum Tubes Hot SRCC Certified
Best for: Large households with high daily hot water demand
This is aimed at families or multi-unit properties that draw heavy volumes of hot water daily. The split system layout separates the collector from the storage tank, which helps when roof space and tank location are constrained.
Key specs
- 1000 liter storage tank
- Single coil heat exchanger
- Evacuated vacuum tube collector
- 45 degree collector frame
- SRCC certified (per listing)
Pros
- Large storage buffers cloudy days
- Evacuated tubes perform well in cold weather
- Split layout gives flexible tank placement
Cons
- Large tank requires significant floor space and structural support
- Single coil offers less flexibility for auxiliary heat integration
Bottom line: Best suited to larger homes with the space and structure to handle a 1000 liter tank.
400 Liter Water Heater Active Split System Dual Coil Tank 45 Deg Frame Evacuated Vacuum Tubes Hot SRCC Certified
400 Liter Water Heater Active Split System Dual Coil Tank 45 Deg Frame Evacuated Vacuum Tubes Hot SRCC Certified
Best for: Small homes, cabins and limited mechanical rooms
A 400 liter tank fits smaller households and is easier to place in tight utility rooms. The dual coil design allows a second heat source, such as a gas or electric backup, to be connected to the same tank.
Key specs
- 400 liter storage tank
- Dual coil heat exchanger
- Evacuated vacuum tube collector
- 45 degree collector frame
- SRCC certified (per listing)
Pros
- Smaller footprint than the 1000 liter model
- Dual coil supports backup heating integration
- Evacuated tubes handle cold conditions well
Cons
- Limited storage may be insufficient for large families
- Dual coil plumbing adds some installation complexity
Bottom line: A practical choice for smaller households that want solar with a backup heat connection.
Doheny’s Solar Pool Heating System for Above Ground Pools – Eco-Friendly – 5′ x 10′ Space Saver Collector Kit
Doheny's Solar Pool Heating System for Above Ground Pools – Eco-Friendly – 5' x 10' Space Saver Collector Kit
Best for: Above ground pool owners who want to extend the swimming season
This is a pool heating kit rather than a domestic hot water system, so it fits a narrower use case. It is included because some homeowners consider it when comparing solar thermal options for seasonal water heating.
Key specs
- 5′ x 10′ collector footprint (per listing)
- Designed for above ground pool use
Pros
- Compact space saver collector size
- Straightforward kit for pool owners
- Eco-friendly positioning for pool heating
Cons
- Not designed for household hot water or tank storage
- Output depends heavily on sun exposure and season
Bottom line: Choose this only if your goal is pool heating, not domestic hot water.
Buying Guide
Freeze Protection and Fluid Type
The defining feature of a closed loop solar hot water system is the heat transfer fluid. Most residential designs use propylene glycol, which is less toxic than ethylene glycol and is common in solar installations. Check the rated freeze point, the fluid concentration recommended by the manufacturer, and whether the system includes an expansion tank and pressure relief valve sized for the loop volume.
Good picks for this: Solar Water Heating System Skyline5 Closed Loop, 400 Liter Water Heater Active Split System Dual Coil Tank
Tank Size and Daily Demand
A common planning method is to estimate daily hot water use per person and multiply by the number of occupants. Storage should cover at least one to two days of demand in cloudy weather. Undersized tanks run out early in winter, while oversized tanks waste standing heat. Confirm the usable capacity in the manufacturer documents, since nominal volume and usable volume can differ.
Good picks for this: 1000 Liter Water Heater Active Split System Single Coil Tank, 400 Liter Water Heater Active Split System Dual Coil Tank
Coil Configuration and Backup Heating
A single coil tank connects one heat source, usually the solar loop. A dual coil tank adds a second connection for an auxiliary heater, such as gas or electric, so the stored water can be topped up on overcast days. If you plan to add backup heat later, a dual coil design avoids retrofitting. Confirm the coil surface area and the connection sizes match your plumbing.
Good picks for this: 400 Liter Water Heater Active Split System Dual Coil Tank, 1000 Liter Water Heater Active Split System Single Coil Tank
Collector Type and Efficiency
Evacuated tube collectors use a vacuum layer to reduce heat loss, which generally helps in cold and windy conditions. Flat plate collectors are simpler and less expensive to build but can lose more heat in winter. Look at the stated collector area, absorber coating and the test certifications listed by the manufacturer. Systems with SRCC certification have published performance data you can compare.
Good picks for this: 1000 Liter Water Heater Active Split System Single Coil Tank, 400 Liter Water Heater Active Split System Dual Coil Tank
Mounting Angle and Roof Fit
Collector tilt should roughly match your latitude for year-round performance, with adjustments for winter-heavy or summer-heavy use. Many split systems use 45 degree frames for mid-latitude installations. Measure your roof pitch, orientation and shading before buying. Remember that the collector and tank may need separate mounting points, and the tank must be placed at or above the collector level so the loop drains properly.
Good picks for this: Solar Water Heating System Skyline5 Closed Loop, 400 Liter Water Heater Active Split System Dual Coil Tank
Installation and Maintenance Requirements
Closed loop systems need periodic fluid checks, pressure monitoring and pump maintenance. Plan for access to the expansion tank, the pump and the isolation valves. Building codes often require a licensed plumber or electrician for connections, and local permitting may apply. If you are not experienced with hydronic systems, a professional installation is advisable. Consult a licensed professional before modifying gas, electrical or structural elements.
Good picks for this: Solar Water Heating System Skyline5 Closed Loop, Doheny’s Solar Pool Heating System for Above Ground Pools
Application Fit: Domestic Hot Water vs. Pool Heating
Domestic hot water systems need insulated storage, potable-rated components and code-compliant connections. Pool heating kits are designed for lower temperature targets and do not store water for household use. Matching the system to the job prevents the common mistake of using a pool kit for a home water heater. Always confirm the intended use on the product listing and in the manufacturer documentation.
Good picks for this: Doheny’s Solar Pool Heating System for Above Ground Pools, Solar Water Heating System Skyline5 Closed Loop
FAQ
What is a closed loop solar hot water system?
A closed loop solar hot water system circulates a heat transfer fluid, usually a glycol and water mix, through the collector and a heat exchanger. The potable water you use is heated indirectly, so it never enters the collector. This protects the system from freezing damage in cold climates.
Is propylene glycol safe for a closed loop solar system?
Propylene glycol is generally considered less toxic than ethylene glycol and is widely used in solar thermal systems. Because the loop is separate from drinking water, the risk is limited, but you should follow the manufacturer’s fluid specification and avoid unapproved additives. Consult a licensed professional for specific safety questions.
How often should the glycol be checked?
Most manufacturers recommend checking fluid concentration, pH and system pressure at least once a year, with more frequent checks in harsh climates. Replacement intervals vary by product, so follow the documentation for your specific model.
How big a tank do I need?
Start with your daily hot water use per person, then multiply by the number of occupants. Choose storage that covers one to two days of demand, adjusting for your local sunshine. Compare usable capacity rather than nominal capacity when sizing.
Can I add a backup heater?
Yes, if the tank has a second coil or auxiliary port. Dual coil tanks make this easier. Backup heating is commonly gas or electric, and the connection must meet local plumbing and electrical codes.
Do I need a permit to install one?
Many jurisdictions require permits for solar thermal and plumbing work. Check with your local building department before installation and consider hiring a licensed installer.
What is the difference between a closed loop and a drainback system?
A closed loop system keeps the antifreeze fluid circulating under pressure, while a drainback system drains the collector when the pump stops. Drainback avoids glycol but needs careful slope and tank placement. Each approach suits different climates and installation layouts.
Conclusion
For most homeowners, the Solar Water Heating System Skyline5 Closed Loop is the most complete starting point, since it is built around the closed loop concept. Larger households with the space and structural capacity should consider the 1000 liter split system, while smaller homes or those planning a backup heater will find the 400 liter dual coil tank a better match. The Doheny’s pool kit is appropriate only for pool heating, not household hot water. Match the tank size to your daily demand, confirm the coil layout, and verify freeze protection and local code requirements before purchasing.
Sources
- Federal guidance on solar water heating types, components and system sizing (energy.gov)
- Standards and technical resources for hydronic and solar thermal system design (ashrae.org)
- Research data on solar thermal performance and system efficiency (nrel.gov)
Related reading
- 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 Compareds (2026)
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.
