The crucial role of expansion tanks in tankless water heaters: ensuring longevity and peace of mind

Tankless water heaters have become increasingly popular due to their energy efficiency and endless hot water supply. However, one common question that arises is whether an expansion tank is necessary for these water heaters. This blog post will delve into this topic, exploring the role of expansion tanks, their necessity for tankless water heaters, and the potential consequences of not having one.

What is an Expansion Tank?

An expansion tank is a pressurized vessel that absorbs the expansion of water as it heats up. When water is heated, it expands in volume, which can put pressure on the water heater and plumbing system. An expansion tank provides a buffer for this expansion, preventing excessive pressure buildup and potential damage.

Do Tankless Water Heaters Need Expansion Tanks?

The short answer is: yes. Tankless water heaters require expansion tanks for the following reasons:

• Pressure Relief: As mentioned earlier, water expands when heated. Tankless water heaters heat water instantaneously, which means the expansion occurs rapidly. Without an expansion tank, this rapid expansion can cause pressure spikes that can damage the water heater, pipes, and other fixtures.
• Thermal Expansion: Tankless water heaters do not have a large storage tank like traditional water heaters. This means that the water heated by the tankless unit expands directly into the plumbing system. An expansion tank accommodates this thermal expansion, preventing pressure buildup.
• System Protection: Expansion tanks protect the entire plumbing system from excessive pressure. High pressure can cause leaks, burst pipes, and even damage to appliances connected to the water supply.

Consequences of Not Having an Expansion Tank

If a tankless water heater is not equipped with an expansion tank, the following consequences can occur:

• Premature Water Heater Failure: Excessive pressure can strain the water heater, leading to premature failure and costly repairs or replacements.
• Plumbing Damage: High pressure can cause leaks, bursts, and damage to pipes, fittings, and appliances connected to the water supply.
• Reduced Water Flow: Pressure buildup can restrict water flow, resulting in reduced hot water pressure at faucets and showers.
• Water Hammer: Expansion without an expansion tank can create water hammer, a loud banging noise that can damage pipes and appliances.
• Safety Hazards: Excessive pressure can pose safety hazards, including scalding from burst pipes or leaks.

Choosing the Right Expansion Tank

When selecting an expansion tank for a tankless water heater, consider the following factors:

• Tank Size: The tank size should be appropriate for the water heater’s flow rate and the volume of water in the plumbing system.
• Pre-Charge Pressure: The pre-charge pressure of the tank should match the static pressure of the water supply.
• Location: The tank should be installed close to the water heater and at the highest point in the plumbing system.

Installation and Maintenance

• Installation: Expansion tanks should be installed by a licensed plumber to ensure proper sizing, placement, and connection.
• Maintenance: Expansion tanks require minimal maintenance. However, it’s recommended to periodically check the pre-charge pressure and inspect for any leaks or damage.

Alternatives to Expansion Tanks

In some cases, alternative methods can be used to address expansion in tankless water heater systems:

• Pressure Relief Valve: A pressure relief valve can be installed to release excess pressure, but it’s not as effective as an expansion tank.
• Water Heater Sizing: Oversizing the tankless water heater can reduce the rate of expansion and minimize the need for an expansion tank.
• Accumulator Tank: A small accumulator tank can be installed to absorb expansion, but it has a limited capacity compared to a full-sized expansion tank.

Wrap-Up: The Necessity of Expansion Tanks

Expansion tanks play a crucial role in the safe and efficient operation of tankless water heaters. By absorbing water expansion, they prevent excessive pressure buildup, protect the plumbing system, and extend the lifespan of the water heater. While alternative methods may be considered in certain situations, an expansion tank remains the most comprehensive and effective solution for expansion management in tankless water heater systems.

Frequently Asked Questions

Q: Can I use a tankless water heater without an expansion tank?
A: It’s not recommended. Without an expansion tank, excessive pressure can damage the water heater, plumbing system, and appliances.

Q: How often should I check the expansion tank?
A: Periodically check the pre-charge pressure and inspect for leaks or damage.

Q: What happens if the expansion tank fails?
A: A failed expansion tank can lead to pressure buildup and potential damage to the water heater and plumbing system.

Q: Can I install the expansion tank myself?
A: It’s recommended to have the expansion tank installed by a licensed plumber to ensure proper sizing, placement, and connection.

Q: What are the benefits of using an expansion tank with a tankless water heater?
A: Expansion tanks prevent pressure buildup, protect the plumbing system, extend the life of the water heater, and reduce the risk of water hammer.