Thermal Expansion and Water Heaters
Thermal expansion is the term used to describe the expansion of water volume due to heating. All water heaters, regardless of heat-source can experience thermal expansion. In every tank-type water heater, cold water is heated as it enters the water heater tank. The heating increases the overall water volume and pressure inside the tank and must be relieved to avoid the potentially adverse effects of thermal expansion.
To understand the importance of a thermal expansion tank, it is first helpful to provide some background information on thermal expansion. When water heats in a tank-type water heater from room temperature to 120 degrees Fahrenheit, it causes the water to expand. This phenomenon is known as thermal expansion. For example, when 40 gallons of cold water is heated to 120 degrees Fahrenheit or more it expands to 40.6 gallons. A thermal expansion tank manages the thermal expansion, the extra .6 gallons, and the system water pressure.
Thermal Expansion Tanks
A thermal expansion tank or expansion vessel is a small tank used to protect closed (i.e., not open to atmospheric pressure) domestic hot water systems from excessive pressure. The modern vessel is a small container or tank divided in two by a rubber diaphragm. One side of the thermal expansion tank attaches to a home’s water supply system that contains water. The other side of the tank, or dry side, holds air under pressure. The tank also has a Schrader valve (car-tire type valve stem) for checking pressures and adding air when needed.
Open and Closed Domestic Hot Water Systems
At one time, residential hot water systems were “open” systems and did not have any backflow prevention capabilities. Consequently, when the volume of heated water exceeded water heater tank capacity, it simply flowed back out to the city water main or water well.
Current plumbing regulations require the integration of backflow preventers or check valves into a residential water heating system, to prevent a home’s water from backflowing into the city water supply system and potentially contaminating it. Residential hot water systems with check valves or backflow preventers are designated “closed” systems. In a closed system, one without any thermal expansion devices, the expanded water has no place to go, the resulting pressure increases will cause a water heater’s temperature and pressure (T&P) relief valve to trigger, subsequently expelling the additional pressure and water volume through the valve.
The Negative Effects of Thermal Expansion
Even before the T&P relief valve is triggered (usually at 150 psi), excessive pressure levels caused by thermal expansion can exert forces that have adverse effects on your hot water system, such as:
About T&P Valves
A water heater’s temperature and pressure (T&P) relief valve is designed as a safety device, used primarily in emergency situations, to relieve pressure caused by thermal expansion. Relying solely on the T&P valve to accommodate for thermal expansion wastes water and energy and may cause the valve to prematurely fail. A better solution is a thermal expansion tank.
Thermal Expansion Tanks – A Simple Solution to Thermal Expansion
A thermal expansion tank is the solution for thermal expansion problems. A thermal expansion tank is a small, pre-pressurized tank with a compressible air cushion (diaphragm) that is installed on the supply side (cold water inlet) of a water heater. The process of thermal expansion:
The thermal expansion tank and this simple process eliminates the potentially detrimental effects of thermal expansion.
Why Install a Thermal Expansion Tank
The reasons to install a thermal expansion tank are that it:
We correct and fix irritating and potentially dangerous condition such as:
If expansive or high-water pressure conditions exist in a home, we can:
The sooner the better when it comes to fixing an expansive water problem. Fixing the problem as soon as possible minimizes any potential damage to your water heater and water supply system.
When to install a Thermal Expansion Tanks
The installation of a thermal expansion tank is recommended/required when any of the following occurs:
When to Contact GPS Plumbing
Thermal expansion of water in home’s water supply system can create several irritating and potentially dangerous conditions including:
When you notice, any of these conditions call GPS Plumbing.