Open or Closed Water Heater System: Which is Better?

Choosing between an open or closed water heater system is a pivotal decision that homeowners must make when installing a new electric or gas water heater.

This choice is not just about ensuring a consistent supply of hot water; it's about safeguarding the longevity of the water heater, protecting your property, and ensuring the safety of the system's users.

Understanding the mechanics, benefits, and potential drawbacks of both open and closed systems is crucial to making an informed decision.

Temperature's impact on water heater safety and performance

expansion tankExpansion tank is often required in closed systems (photo: amazon)

Water tank heaters, irrespective of their type, operate on a basic principle: they heat water stored in a tank, which increases the water's temperature, pressure, and subsequently, its volume.

A study by the water heater manufacturer Rheem highlighted a significant increase in water pressure with a moderate rise in temperature: when water temperature escalates from 75°F to 100°F, the pressure can jump from 80 PSI (pounds per square inch) to a staggering 520 PSI.

Water heaters are typically designed to handle a working pressure of around 150 PSI, with safety tests conducted at pressures up to 300 PSI to ensure durability.

However, if the internal pressure exceeds this threshold, it can lead to tank deformation, bulging, and eventually, leaks or catastrophic failure.

This is where the temperature and pressure relief (TPR) valve plays a critical role by releasing hot water to decrease pressure, thus preventing damage.

Open or closed water heater system? What's the difference?

When it comes to setting up a water heater in your home, you're faced with two primary options: the open system and the closed system.

Each setup offers distinct advantages and considerations that can impact the efficiency and safety of your water heating solution.

Bellow you will find specifics of both systems, helping you make an informed decision that best suits your household's needs.

Open water heater system

An open water heater system allows for the free movement of expanded water back into the cold water supply, and potentially into the municipal supply, if the pressure is sufficient.

This setup relies on the absence of any one-way valves (such as shut-off valves or check valves) that would otherwise block this reverse flow.

In scenarios where the water expands due to heating, the open system ensures that the pressure within the water heater remains equivalent to the incoming supply pressure, thus averting the risk of over-pressurization.

However, to prevent potential backflow of water into the municipal system, many local codes mandate the installation of check valves and shut-off valves, thereby unintentionally creating a closed system environment.

Closed water heater system

Conversely, a closed water heater system is designed to prevent the mixing of heated water with the municipal supply by employing various valves (check valves, pressure-reducing valves, backflow preventers, etc.).

While this arrangement effectively isolates the home's hot water supply, it also traps expanding water within the system. Without an avenue for the excess pressure to escape, the risk of reaching critical pressure levels increases, which can activate the TPR valve.

Should the TPR valve fail to operate correctly, the system is at risk of developing dangerously high pressures, leading to potential tank rupture or failure.

To mitigate these risks, the installation of an expansion tank is often required in closed systems. Expansion tanks are engineered to accommodate the increased water volume, thereby reducing pressure within the system to a manageable level.

This not only ensures the system's safety and efficiency but also complies with local building codes that aim to prevent pressure-related damages.

emergency plumber

Tips for homeowners

Regular maintenance and inspection schedules

  • Consider a thermal expansion valve: This valve is essential for controlling pressure caused by thermal expansion in closed systems. Installing one can prevent unnecessary stress on your water heater.
  • Regularly inspect the TPR valve: The temperature and pressure relief valve is a critical safety feature. Inspect it annually to ensure it's operational, as it releases excess pressure and prevents tank damage.
  • Flush your system annually: Sediment buildup can impair your water heater's efficiency and lead to corrosion. Draining and flushing your tank yearly can extend its lifespan and improve performance.

Signs of overpressure and when to consult a professional

  • Monitor water pressure: Use a pressure gauge to regularly check your system’s water pressure. Consistently high readings may indicate a malfunctioning pressure relief system or an issue with thermal expansion.
  • Look for signs of overpressure: Unexplained leaks, a constantly leaking TPR valve, or banging noises from the tank are indicators of overpressure. If you observe these, shut off your water heater and contact a professional.
  • Use pressure reducing valves: If your home's incoming water pressure is too high, a pressure-reducing valve can protect your water heater and plumbing system from damage due to overpressure.

Importance of professional installation and consultation

  • Consider an anti-scald mixing valve: Professional installation of an anti-scald mixing valve can prevent excessively hot water from reaching taps, protecting against burns and ensuring comfortable water temperature.
  • Balance system pressure: A professional can install balancing valves or recommend adjustments to ensure consistent water pressure, enhancing comfort and protecting the system.
  • Upgrade to a water heater with built-in protection: Modern water heaters often come with advanced safety features, including built-in thermal expansion protection. A professional can help you select and install a model that best suits your needs.

Making the right choice

Deciding between an open and closed water heater system depends on several factors, including local building codes, the specific needs of your household, and the existing plumbing setup.

Open systems, while simpler, may not be feasible or legal in all areas due to the potential for backflow.

Closed systems, though more complex, offer greater control over water pressure and are adaptable to a wider range of plumbing configurations.

In either case, understanding the dynamics of water expansion and pressure regulation is crucial. Proper installation and regular maintenance, including checking the TPR valve and expansion tank, are essential for the longevity and safety of the system.

In summary, both open and closed water heater systems have their merits and challenges. A thoughtful assessment of your home's requirements, compliance with local regulations, and a commitment to ongoing maintenance can guide you to the best solution for your hot water needs, ensuring a reliable, safe, and efficient water heating setup.

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