thermal expansion relief valve vs expansion tank

Thermal Expansion Relief Valve vs Expansion Tank – Guide

Advanced plumbing techniques necessitate installing relief devices often to handle increasing water. The use of thermal expansion relief valves and expansion tanks constitute two of the most used methods for adjusting for water expansion. Thermal expansion relief valves, as well as expansion tanks, provide an exit for vapour and airflow when the water temperature gets hot. Although they accomplish similar tasks, they go about them in unique ways. So, let us find out, thermal expansion relief valve vs expansion tank: Which is the best? Let us begin.

What Exactly is a Thermal Expansion Relief Valve?

Thermal safety and thermal expansion relief valves are additional names for thermal relief valves. It is a preventive measure used in pipes and fluid fittings to safeguard the machinery and infrastructure.

The thermal relief valve opens to expel partial flow and reduce the stress to a safe level when the heat expansions of fluid lead to elevated pressure within an isolated circuit. In principle, the fluid expands slightly as it warms up.

If somewhat not by an extremely significant amount, the quantity increase of the fluid may raise the pressure difference when the temperature rise is relatively high.

Thermal relief valves work well to defend against this pressurization scenario and prevent catastrophe.

Thermal safety controls are utilized when heating accumulation may be an issue, such as lengthy tunnels or tubes subjected to environmental factors (such as direct sunlight), sealed containers, or hot water system purposes. 

What Exactly Is an Expansion Tank?

An expansion tank is a separate modest container that is connected to the water heater’s main pipe and absorbs stress. An expansion tank is intended to release pressure in enclosed hydronic heating circuits as well as potable water supplies.

In order to prevent harm from increased stress, it makes sure that steady force is kept inside the tubes. An expansion tank in a heater is an important factor that safeguards the overall structure from the higher volume and pressure that is created by temperature.

Water needs to expand as its temperature rises. There is only a limited amount of room in the heater and pipelines in an enclosed heater. The force will rise and potentially harm the structure, usually in its vulnerable places.

An expansion tank is intended to reduce load, extending the lifespan of all the thermal system’s parts. To avoid high pressure, the expansion tank is made to accommodate the thermal increases of fluid as it warms up inside the water heaters. 

Thermal Expansion Relief Valve vs Expansion Tank

Expansion Tank: An Overview

Generally, the expansion tank served as the solution to heat flow. It is customary to put this miniature metal tank-like item on the chilled water entrance of the hot water system.

Given that water expands by roughly 4 percent when warmed to boiling (100 °C), and so by around 2 percentage points when warmed from 15 °C to 50 °C, a 2-gallon7.5 litres enlargement tank is sufficient for most 100, 150-litre heating systems.

Expansion Tank

The bottom half of an expansion tank is stuffed with air (usually at 12 psi pressure), whereas an elastic bladder added halfway through the tank enables liquid entering from the upper to force down on the gas beneath.As a result, warm liquid expanding from a hot water system can securely fill the upper house of an expansion tank till stress is alleviated by switching on a warm water tap.

Thermal Expansion Relief Valve: An Overview

A TERV is usually a ball valve with a low-pressure, spring-loaded safety valve. The safety valve will engage (often at pressures ranging from 100 to 125 psi) to allow warm water to flow out of a boiler, whereas the ball valve is a code-approved mechanical shut-off.

Most TERVs used in home piping are designed to discharge liquid that has reached levels of between 100 and 125 psi. Remember that this is considerably below the 150 psi level where a water heater’s PRV is tuned to release and discharge additional pressure. As a result, the TERV serves as the first line of defence, maintaining pressure from rising over 125 psi.

As warm liquid rises from the boiler, the flow in the tube results in the TERV increasing to the value specified by the valve, perhaps 100 psi. The excess heat is now ejected into a few-foot-long output pipe that normally leads to a sewer, where it may properly drain out once the spring-loaded valve is pulled open at this stage.

Which One is Better?

As mentioned earlier, the function of expansion tanks and relief valves remains identical, although their appearance and functionality are distinct. Here are some summaries and differences between both systems:

  • The expansion tank is eco-friendly. Although both systems work to release excess pressure inside the tubes, the TREV discharge the excess water while the expansion tank holds the water, which causes water wastage in the TREV unit.
  • The maintenance of the TREV is lower than the expansion tank. Even though the TREV drains the water into sewage, it is more reliable and costs less to maintain.
  • The lifespan of the TREV is higher than the expansion tank. The TREV may live up to 10 years instead of an expansion tank that only functions for 2 to 6 years.
  • The TREV is easy to instal than the expansion tank. A professional can install a TREV unit within half an hour, while the expansion tank takes roughly an hour.
  • The installation cost of TREV is less than the expansion tank. TREV costs around 70 USD, while the expansion tank costs more than 100 USD.

What Occurs If a Relief Valve or Expansion Tank Malfunctions?

The system cannot provide hot water anymore if the TREV breaks. Moreover, an outburst may result from a PRV failure. Gear breakage, a disruption in workflow, and even physical harm are possible outcomes. 


As you may see from the comparison, the Thermal Expansion Relief Valve could be your choice if you want a dependable, easy-to-work-with, long-lasting product in your hands. However, the expansion tanks can save water alongside giving all these capabilities. 

We hope, with the help of this article, you may choose which is better for you according to your needs.

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