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Water heater expansion tank

Hot water heater expansion tanks

The addition of a hot water heater expansion tank can both resolve and prevent high water pressure. If either undetected or unresolved, excessive pressure can seriously compromise the durability, performance and the efficiency of the system.

Inspecting for high pressure is an important water heater maintenance procedure that should be performed periodically. A storage tank with pressure that exceeds 80 psi (pressure per square inch) when the heating element is on and hot water is not in use will require an expansion tank in most cases.

With that said, storage tanks that don't experience high water pressure stand to benefit as well. Before installing an expansion tank consider the following;

Warning - High Water Pressure and Gas Powered Storage Tanks

Overtime excessive pressure can become a serious safety concern in gas water heating tanks. High water pressure can ultimately compromise, or even collapse,
the internal flue that's immersed within the storage tank.

Internal flue damage can result in the build up of carbon monoxide, which is very dangerous. If your water heating storage tank has high water pressure and you suspect that the internal flue may have been damaged or compromised, consult with a local water heating professional immediately.

Thermal expansion

Thermal expansion occurs in all systems. When the heating element significantly raises the temperature of the domestic water, the volume of the water increases.

The additional volume created by thermal expansion must be accounted for. If the additional volume is not accounted for and hot water is not being used, excessive pressure can build up within the systems' storage tank.

High water pressure can compromise the durability (and the performance) of the system, potentially causing the tanks temperature pressure relief valve to leak as well as shower heads and faucets. A hot water heater expansion tank is the cost effective solution to thermal expansion and high water pressure.

Temperature Pressure Relief Valve and Thermal Expansion

The temperature pressure relief valve is a safety feature designed to operate as an emergency relief control and not as a constant thermal expansion control. If the storage tank pressure continually increases, it can cause the T & P valve to operate frequently, which can ultimately result in the failure of the valve.

Closed Water Systems

Many municipalities have back flow preventers or check valves that are installed at the water meter. This means that in most homes today, the water that enters from the municipal supply is prevented from ever reentering.

In the past the additional water volume created by thermal expansion could flow back into the municipal supply, relieving pressure. With the addition of back flow preventers and check valves, these homes now have closed water systems.

Expansion Tanks and Plumbing Codes

The International Association of Plumbing and Mechanical Officials developed the Uniform Plumbing Code. The Uniform Plumbing Code, and many local building and plumbing codes, require a storage tank to be equipped with a hot water heater expansion tank to control thermal expansion in closed water systems.

Unfortunately many existing homes with closed water systems are not equipped with expansion tanks. The same is true with new water heating storage tanks. Often times thermal expansion tanks are not installed during replacement, even though local codes often recommend thermal expansion protection.

Manufacturer Guidelines and Warranty

Many manufacturers of storage water heaters today recommend that expansion tanks be installed before high water pressure is a problem. This is especially the case with gas powered storage tanks because the rate of thermal expansion is often greater than with electric powered tanks.

In many cases, failure to install a hot water heater expansion tank can result in the manufacturer warranty becoming null and void.

Necessary? What's Recommended

When installing a new storage tank water heater, protect your investment and follow the manufacturers recommendations. If the manufacturer recommends an expansion tank, then install one regardless of local plumbing or building codes.

Homeowners with closed water systems should check the existing storage tank and verify whether or not an expansion tank is present. If an expansion tank or a pressure reducing valve is not present, referencing the owners manual or the local plumbing codes (with regard to thermal expansion control) would be wise.

Homeowners with closed water systems and high water pressure exceeding 80 psi (when the heating element is activated and water is not being used) should install a hot water heater expansion tank, unless the manufacturers guidelines specifically recommend not installing one.

Even if the manufacturer doesn't specifically recommend installing an expansion tank, it's important to note that the thermal control provided rarely compromises the existing product warranty, and it will further protect the tank from failure.

How expansion tanks work

Water heater expansion tanks are generally small and light weight. These tanks often contain a pressurized internal compartment (often referred to as a bladder) along the bottom, and a polypropylene lined internal compartment along the top. In most cases, in between both compartments is a flexible diaphragm.

When thermal expansion occurs the additional hot water volume fills the internal compartment along the top of the tank. As the pressure increases, the flexible diaphragm compresses the pressurized bottom compartment, making more room for the additional water volume.

Sizing expansion tanks

Hot water heater expansion tanks are small, but there available in several sizes. There are two important considerations to make when sizing an expansion tank; the incoming or supply water pressure and the volume of the storage tank.

Determining Incoming or Supply Water Pressure

A homes' incoming water pressure is largely determined by the local municipality or the local water source. From mile to mile, the supply water pressure can vary significantly. Determining a homes' supply water pressure is fairly easy.

Pressure can be determined by fitting a water pressure gauge on a faucet or an outdoor fixture, 40 psi to 80 psi is generally considered an acceptable range. The local municipality can be contacted to perform an on site evaluation as well.

Selecting the Right Expansion Tank

In an attempt to assist would be consumers determine which expansion tank is best suitable, many reputable manufacturers display sizing and selection guides (as well as labels) on their products.

These guides and labels are broken down by incoming or supply water pressure and water heater storage tank volume. Many manufacturers offer tanks that are internally pre pressurized as well. In some instances, additional pressure can be added to accommodate those systems with higher water pressure.

Expansion tank installation

Installing a hot water heater expansion tank is a relatively easy project. Detailed installation instructions and guidelines are generally provided. It's always wise to follow the manufacturers' instructions and guidelines as carefully as possible.

Installation Guidelines

Generally a single tee plumbing fixture is required to install the expansion tank on the existing water pipe. Some industry professionals suggest using plumbing hangers as well for additional support. This is especially the case in homes that have PVC, or plastic, plumbing pipes.

Cold Water Pipe or Hot Water Pipe Installation?

Most manufacturers recommend installing a hot water heater expansion tank on the cold water supply pipe. Some professionals suggest that installation on the hot water pipe is equally as effective.

Other industry professionals suggest that installation on the hot water pipe can have adverse effects on the longevity of the water heater expansion tank.

When in doubt, always follow the manufacturers' installation guidelines.

Horizontal Installation or Vertical Installation?

Many industry professionals recommend installing expansion tanks on horizontal pipe runs if possible. With that said many manufacturers insist a horizontal or a vertical installation has no tangible effect on the amount of protection the tank will provide. When in doubt, refer to the manufacturers' installation guidelines.

More on water heater maintenance

  • Water Heater Maintenance; how to extend the life of an old or recently purchased storage tank.
  • Water Heater Anode; periodically inspecting the sacrificial anode rod is a maintenance procedure that protects the storage tank from corrosion.
  • Drain Hot Water Heater; draining or flushing the storage tank removes sediments that can compromise efficiency and volume.
  • Water Heater Drain Valve; inspect the drain valve on the tank for potential leaks and drips.

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