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Open vs Closed Circuit Solar Hot Water Systems

Solar hot water system panels on home roof

When people think of energy efficiency, solar panels are often the first thing that comes to mind. Like most types of heaters, there are different kinds of solar water heating systems on the market, and it’s important to be aware of each so you can make an informed decision. With solar water heaters, you’ll soon discover that they’re either categorised as open or closed circuits. Let’s compare the two and weigh up each system’s advantages and disadvantages. 


What is the difference between an open loop and closed loop water heating system?

The key difference between the two system types is how they operate and heat your water. An open loop system heats the water you will use and stores it. 

A closed-loop system will heat an anti-freeze and water solution that transfers heat to your domestic water. Each system has its pros and cons, so you’ll need to weigh up your own situation when determining which type of hot water heater is best for your home.


How Does an Open Circuit Solar Hot Water System Work

An open-circuit solar hot water system is considered an active system that doesn’t need a heat exchanger.

The most basic model of an open loop system is what is known as an integral collector or batch collector. These systems have multiple pipes or storage tanks and are plumbed into your house’s domestic hot water system. More advanced systems will feature a separate insulated storage tank that uses a circulator powered by electricity. Some systems also feature photovoltaic pumps to help prevent freezing.


If you live in an area where the temperature stays above freezing, an open circuit system should work for you. However, in colder areas, you’ll need additional features to avoid freezing water in your pipes. While this will help prevent your water from freezing, it can have negative effects on your system’s temperature sensors and wastes heat, energy and water.

Source: https://www.fsec.ucf.edu


How Does a Closed Circuit Solar Hot Water System Work?

The setup of a closed-circuit solar hot water system is inherently more complex mechanically. Rather than directly heating the water itself, a closed-circuit solar system uses anti-freeze in a coil within the storage tank to heat water. This can be a huge advantage in any area where temperatures drop below a certain level in the cold season.

In a drain-back system, the opposite occurs, with warmer water being pumped into the storage tank. The distilled water is only in the tank when necessary, which helps avoid freezing issues that can come with an open loop system. 

Closed loop heaters are often passive systems (or a thermosiphon system) meaning they don’t require an outside power source. 

Same Day Hot Water - Closed Loop Solar Hot Water System Technical
Source: Dummies.com


Pros & Cons of an Open Loop Solar Hot Water System


  • The simplest system to design and install.
  • Needs the least amount of construction.
  • Potentially can go longer without maintenance.
  • Usually the more affordable option.



  • Open loop systems struggle in freezing temperatures.
  • If water freezes in pipes, it can cause a rupture which is expensive to repair.
  • Preventative measures to avoid the above issue will add to your costs.
  • If you don’t use water quickly enough, you may experience heat loss. 


Pros & Cons of a Closed Loop Solar Hot Water System


  • Better equipped to handle colder climates.
  • More reliable in delivering hot water.
  • Less energy and heated water wasted.


  • Usually more expensive.
  • More complicated systems and setups.


The Final Verdict: Which is Better, an Open or Closed Solar Hot Water System?

The answer to this will come down to your personal circumstances. Open loop systems have a distinct disadvantage in cold climates. However, depending on where you are in Australia, this may not be a big issue. If you’re moving to a new area, keep in mind that some places in Australia get a lot colder in winter than you would expect. 


A closed solar hot water system is a more versatile system that can work in a wide range of environments to provide warm household water. They are popular in the Northern Hemisphere in countries that experience snow, but they can be lifesavers in Australia as well. If you live in one of the southern states where the temperatures drop to freezing, a closed system is your best choice.



Talk to the experts about the best solar hot water heater for you

Considering what the best solar water heater is for you? Same Day Hot Water Services has a range of solar systems to meet your hot water usage needs. Whether you are looking for help with installation, repairs or maintenance, our friendly team has all your needs covered. 

Get in touch today to discuss how we can help you with your hot water needs.


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