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Thermal Expansion Tanks: Part 2 – Sizing

July 31, 2015 by Roger Griffith Leave a Comment

How To Size Thermal Expansion Tanks For Hot Water Systems

thermal expansion tank

Referring to sizing tables in an expansion tank manufacturer’s catalog is the easiest method, although not the best method, for sizing thermal expansion tanks. Sizing tables provided by the manufacturers, give the tank model number and size based on the water heater’s volume and the system supply pressure. These tables, however, are based on three important assumptions that designers need to be aware of.

First, for most manufacturers, the tables are based on a maximum allowable line pressure of 150 psi. This is the maximum allowable working pressure of most water heaters and thermal expansion tanks. It is also the setting of the water heater relief valve. In other words, the thermal expansion tank, if selected by the tables, could accommodate the thermal expansion up to a system pressure of 150 psi, which is the relieving point for the water heater relief valve. Remember that the purpose of the thermal expansion tank is to avoid the relief valve from relieving. Sizing the thermal expansion tank for a maximum allowable pressure of 135 psi, which is 10% below the relief valve set point, is a better alternative.

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Filed Under: Hot Water Systems, Recent Posts Tagged With: hot water system, plumbing design, thermal expansion tanks

Tankless Water Heaters and Thermal Expansion Tanks

June 21, 2015 by Roger Griffith Leave a Comment

tankless water heater schematic

Thermal expansion tanks are typically installed in conjunction with storage water heaters, but what are the requirements for tankless water heaters and thermal expansion tanks? This scenario is sometimes overlooked. Let’s look at the specifics.

Section 607.3 of the 2012 International Plumbing Code (IPC) provides the requirements for controlling pressure from thermal expansion. The requirements contained in paragraphs 607. 3 and 607.3.1 do not specifically distinguish between thermal expansion from a storage water heater, a tankless water heater, or other system equipment. Paragraph 607.3.2 does specifically require a device for controlling pressure “when there is a backflow prevention device, check valve or other device installed on the water supply system utilizing storage water heating equipment such that thermal expansion causes an increase in pressure.”

The IPC does not specifically require a thermal expansion tank or other device be installed with a tankless water heater. However, if a storage tank is used in conjunction with a tankless water heater in a closed system, which is sometimes the case with recirculation, then a means of controlling thermal expansion must be provided.

[Read more…]

Filed Under: Hot Water Systems, International Plumbing Code, Uncategorized, Water Heaters Tagged With: thermal expansion tanks, water heaters

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Roger W. Griffith, P.E.
(865) 471-8142
RGriffith@GriffithEngineering.net

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Jefferson City, TN 37760
(865) 471-8142

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