# Expansion tank



## jmc (May 15, 2014)

Hello.

IRC2006. Are expansion tanks required on residential water heaters? I see in sec 2003 that only boilers req one, but, I recall some years ago a coworker pointing me to another sec in the IRC that req one.

Thanks for your help.


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## Frank (May 15, 2014)

They are required when there is a check valve in the supply line like a footvalve on the well or some water meters with integral backplow devices.

This language originated in the 2006 IRC

IPC-- 2012

607.3 Thermal expansion control.

A means of controlling increased pressure caused by thermal expansion shall be provided where required in accordance with Sections 607.3.1 and 607.3.2.

607.3.1 Pressure-reducing valve.

For water service system sizes up to and including 2 inches (51 mm), a device for controlling pressure shall be installed where, because of thermal expansion, the pressure on the downstream side of a pressure-reducing valve exceeds the pressure-reducing valve setting.

607.3.2 Backflow prevention device or check valve.

Where a backflow prevention device, check valve or other device is installed on a water supply system utilizing storage water heating equipment such that thermal expansion causes an increase in pressure, a device for controlling pressure shall be installed.

IRC 2012

P2903.4 Thermal expansion control.

A means for controlling increased pressure caused by thermal expansion shall be installed where required in accordance with Sections P2903.4.1 and P2903.4.2.

P2903.4.1 Pressure-reducing valve.

For water service system sizes up to and including 2 inches (51 mm), a device for controlling pressure shall be installed where, because of thermal expansion, the pressure on the downstream side of a pressure-reducing valve exceeds the pressure-reducing valve setting.

P2903.4.2 Backflow prevention device or check valve.

Where a backflow prevention device, check valve or other device is installed on a water supply system using storage water heating equipment such that thermal expansion causes an increase in pressure, a device for controlling pressure shall be installed.


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## mtlogcabin (May 15, 2014)

M2301.2.6 Expansion tanks.

Expansion tanks in solar energy systems shall be installed in accordance with Section M2003 in closed fluid loops that contain heat transfer fluid

P2903.4 Thermal expansion control.

A means for controlling increased pressure caused by thermal expansion shall be installed where required in accordance with Sections P2903.4.1 and P2903.4.2.

P2903.4.1 Pressure-reducing valve.

For water service system sizes up to and including 2 inches (51 mm), a device for controlling pressure shall be installed where, because of thermal expansion, the pressure on the downstream side of a pressure-reducing valve exceeds the pressure-reducing valve setting.

P2903.4.2 Backflow prevention device or check valve.

Where a backflow prevention device, check valve or other device is installed on a water supply system using storage water heating equipment such that thermal expansion causes an increase in pressure, a device for controlling pressure shall be installed.


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## Builder Bob (May 15, 2014)

P2903.4 Thermal expansion control.

A means for controlling increased pressure caused by thermal expansion shall be installed where required in accordance with Sections P2903.4.1 and P2903.4.2.

P2903.4.2 Backflow prevention device or check valve.

Where a backflow prevention device, check valve or other device is installed on a water supply system using storage water heating equipment such that thermal expansion causes an increase in pressure, a device for controlling pressure shall be installed.

If your water meter has a back flow prevention valve installed, A means for controlling thermal expansion may be required on a water heater IF the heating of water contained within causes an increase in pressure........ Some toilets have a burper design, that will allow the excessive pressure to burp or relief into the toilet tank.


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## Frank (May 15, 2014)

In summary Maybe

During the great Virginia earthquake of August 23, 2011 expansion tanks mounted on top of 1/2 inch CPVC pipe with no other support in a multistory assisted living facility caused the  largest loss in the county when a few the supporting pipes broke and water cascaded down through 4 stories of units.


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## jar546 (May 16, 2014)

Frank said:
			
		

> In summary MaybeDuring the great Virginia earthquake of August 23, 2011 expansion tanks mounted on top of 1/2 inch CPVC pipe with no other support in a multistory assisted living facility caused the  largest loss in the county when a few the supporting pipes broke and water cascaded down through 4 stories of units.


Required by code?  YES with code sections provided above.

Should seismic areas have more stringent requirements, especially due to known history failures?  Yes

Is a past bad experience a reason to not require them?  NO, just install them so you don't have that problem.

JMHO


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## jmc (May 16, 2014)

thank you all for your quick responses.


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## Span (May 16, 2014)

The expansion tank requirement for my understand is when you have a storage tank type water heater and a pressure regulator valve on water main which doesn't have integral bypass function, then you do need to install a expansion tank. otherwise NO.


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## Keystone (May 16, 2014)

Its not just a storage tank. When a plumbing system is has a backflow device installed it creates a closed system which necessitates the expansion tank to absorb thermal shock that will occur from typical household fixtures being used. Without the backflow device the entire water system becomes an expansion tank but lacks prevention of the entire water system, in the event your hooked up weed and feed from the garden hose backflows due to a pressure drop in the main or your neighbors house caused by a break.


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## Frank (May 16, 2014)

Water heated from 40F to 150F will expand 2% in volume or 0.8 gallons for a 40 gallon tank.  Most plumbing systems without an expansion tank do not have this much air in the system so the water has to go somewhere, out the pressure relief valve or backflowing into the public main.  If there is a check valve or PRV on the feed from the source it will open the PRV on a regular basis if an expansion tank is not provided.  If there is no PRV and water is not used it will create high enough pressures to burst something as water at normal pressures is essentially noncompressible.  140F water at 5000 psi will only compress 1% over 140 degree water at normal pressure.  Heating water from 40F to 140F with a fixed volume would generate around 10,000 psi on the enclosure, which is roughly the peak pressure in a shotgun chamber when it is fired..


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