When water is heated it expands. For example, water heated from 90ºF to a thermostat setting of 140ºF in a 40 gallon hot water heater will expand by almost one-half gallon. This is because when water is heated, its density decreases and its volume expands. The installation of a Pressure Reducing Valve (PRV), Check Valve or Back Flow Preventer closes the water system, leaving water with no room for expansion. (National Standard Plumbing code: 10.5.7 requires backflow prevention, to prevent backflow into the water main.) Since water is not compressible, the extra volume created by expansion must go someplace.
Thermal expansion in a closed plumbing system can be damaging, dangerous and costly. Its effects include damage to water heater connections, gas water heater flue tubes, pumps serving washers and dishwashers, leaking faucets, ˝weeping˝ of water through the water heater T&P Safety Valve, and noisy water hammer in the pipes. More serious problems can also occur due to thermal expansion. When dangerous pressures are built up in a water heater, internal parts may fail such as the internal flues, fittings or water connections. If a flue way collapses it can lead to the potential release of toxic gases, such as carbon monoxide into living spaces. Thermal expansion can also lead to a ruptured or distorted hot water heating tank and may void the manufacturer’s warranty. A properly sized expansion tank eliminates these problems, by giving water a place to go when thermal expansion
occurs. When a water heating cycle ends, or when any fixture is opened within the system, the impact of thermal expansion is reduced, and water drains out of the expansion tank back into the system.
Potable and Non-Potable Systems
Potable refers to water in an open domestic hot water heating system. This is water that could potentially be consumed by people and is not recirculated within the system. Non-potable refers to water in a closed hydronic heating, radiant floor heating, or a chilled water system where the water is recirculated and does not leave the system. Each of these hot water heating systems have different thermal expansion requirements.
Indications you may need an Expansion Tank
The most common symptoms that may indicate a thermal expansion problem exists include:
•The water heater relief valve operating to relieve excessive water pressure.
•An excessive water pressure surge when a faucet is opened.
•Increased frequency of faucet washer replacement.
•Metallic expansion noises in the water heater.
•Piping noises, cracking or creaking while the water heater is operating.
•Premature failure of appliance solenoid valves and o-ring seals.
•Severely reduced water heater life.
Plumbing Code Requirements for Thermal Expansion Control
Plumbing codes require that thermal expansion control be addressed in plumbing systems. A temperature and pressure relief valve is not considered a thermal expansion device. This is because when water is allowed to continuously drip from the T&P relief valve, minerals from the water can build up on the valve, eventually blocking it. This blockage can render the T&P valve useless and potentially lead to hot water heater explosions. The International Plumbing Code (IPC), Uniform Plumbing Code (UPC) and Standard Plumbing Code all require thermal expansion control to be addressed. Many manufacturers offer all sorts of solutions for handling thermal expansion, please visit our links section for the websites of the expansion tank manufacturers.
Thermal expansion in a closed plumbing system can be damaging, dangerous and costly. Its effects include damage to water heater connections, gas water heater flue tubes, pumps serving washers and dishwashers, leaking faucets, ˝weeping˝ of water through the water heater T&P Safety Valve, and noisy water hammer in the pipes. More serious problems can also occur due to thermal expansion. When dangerous pressures are built up in a water heater, internal parts may fail such as the internal flues, fittings or water connections. If a flue way collapses it can lead to the potential release of toxic gases, such as carbon monoxide into living spaces. Thermal expansion can also lead to a ruptured or distorted hot water heating tank and may void the manufacturer’s warranty. A properly sized expansion tank eliminates these problems, by giving water a place to go when thermal expansion
occurs. When a water heating cycle ends, or when any fixture is opened within the system, the impact of thermal expansion is reduced, and water drains out of the expansion tank back into the system.
Potable and Non-Potable Systems
Potable refers to water in an open domestic hot water heating system. This is water that could potentially be consumed by people and is not recirculated within the system. Non-potable refers to water in a closed hydronic heating, radiant floor heating, or a chilled water system where the water is recirculated and does not leave the system. Each of these hot water heating systems have different thermal expansion requirements.
Indications you may need an Expansion Tank
The most common symptoms that may indicate a thermal expansion problem exists include:
•The water heater relief valve operating to relieve excessive water pressure.
•An excessive water pressure surge when a faucet is opened.
•Increased frequency of faucet washer replacement.
•Metallic expansion noises in the water heater.
•Piping noises, cracking or creaking while the water heater is operating.
•Premature failure of appliance solenoid valves and o-ring seals.
•Severely reduced water heater life.
Plumbing Code Requirements for Thermal Expansion Control
Plumbing codes require that thermal expansion control be addressed in plumbing systems. A temperature and pressure relief valve is not considered a thermal expansion device. This is because when water is allowed to continuously drip from the T&P relief valve, minerals from the water can build up on the valve, eventually blocking it. This blockage can render the T&P valve useless and potentially lead to hot water heater explosions. The International Plumbing Code (IPC), Uniform Plumbing Code (UPC) and Standard Plumbing Code all require thermal expansion control to be addressed. Many manufacturers offer all sorts of solutions for handling thermal expansion, please visit our links section for the websites of the expansion tank manufacturers.
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