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Expansion Tank for Water Heater

I actually watched that episode of myth busters......flippen cool.

The expansion tank, not until you have a check valve in the system somewhere. Some water providers require a incoming check valve, so yes, need the tank, otherwise...not....
 
So far for me, every single municipal water company in every jurisdiction, in every state I've worked in required a backflow preventer for the house so I am not sure where an expansion tank would not be required.
 
Our City water meters have internal check valves, in addition to high water pressure that requires PRVs at most homes. Yes, expansion tanks are essential.
Last month during the initial the final inspection of a show home in a new development, We noticed that there was water on the garage floor coming from the water heater. And Yes, it was due to high pressure (123#). The plumber had failed to install a PTR valve and an expansion tank. The plumber installed both and the problem was corrected.
 
jar546 said:
So far for me, every single municipal water company in every jurisdiction, in every state I've worked in required a backflow preventer for the house so I am not sure where an expansion tank would not be required.
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Well what with Florida being at the bottom of the country I suppose that the water pressure would be up there.
 
Expansion tanks are fairly inexpensive and easy to install at the time the water heater is installed. I see no reason not to install one with every water heater, even if there is currently no (known) backflow preventer or PRV. You never know when the utility company will decide to upgrade their meters and suddenly you have a check valve in your system.
 
Michael.L said:
Expansion tanks are fairly inexpensive and easy to install at the time the water heater is installed. I see no reason not to install one with every water heater, even if there is currently no (known) backflow preventer or PRV. You never know when the utility company will decide to upgrade their meters and suddenly you have a check valve in your system.
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Makes absolute perfect sense.
 
Paul Sweet said:
Does the water heater also need a separate expansion tank if you're on a well and have a pressure tank?
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As long as you KNOW there are no check valves (including check valves built into other devices) between the water heater and the well system's pressure tank, then no, you do not need an additional expansion tank.
 
jar546 said:
Every well that I have inspected had a checkvalve in the system to prevent backflow to the well.
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Agree. But if there is not a check valve downstream of the pressure tank , then I'd use some judgement and exempt it.

The pressure tank is a expansion tank, only about 10-100 times larger.

**Update** - Larger and it has a full diameter pipe connection (3/4" vs 1/8" for saddle tap expansion tanks)
 
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jar546 said:
Every well that I have inspected had a checkvalve in the system to prevent backflow to the well.
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Every well system must have a check valve upstream of the pressure tank, otherwise the pressure tank would discharge back into the well once the pump stopped. For a submersible pump system, the check valve is typically on the drop pipe just above the pump.

The question is: Is there a check valve downstream of the pressure tank? This would be less common, but certainly possible.
 
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One other thing to consider regarding whether or not to install an expansion tank. If the homeowner (or whoever) shuts off the cold water supply valve that feeds the hot water heater, but forgets to also shut off the water heater thermostat, then there's a risk of the tank bursting if there is no expansion tank.

This is another reason why I advise simply installing an expansion tank for every tank water heater. ALWAYS install the expansion tank between the water heater's cold water supply shut off valve and the water heater.
 
Rick18071 said:
Do you need a water-hammer arrestor if there is a expansion tank?
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Water hammer arrestors should be installed on the piping as close as possible to the device that causes (or could potentially cause) a water hammer event. Typically, these are valves that close very rapidly like the solenoid valves in a washing machine or a toilet flush-o-meter valve.

The expansion tank is too far away from any of these valves to absorb the shock wave (water hammer).
 
Michael.L said:
Water hammer arrestors should be installed on the piping as close as possible to the device that causes (or could potentially cause) a water hammer event. Typically, these are valves that close very rapidly like the solenoid valves in a washing machine or a toilet flush-o-meter valve.

The expansion tank is too far away from any of these valves to absorb the shock wave (water hammer).
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Wouldn't this include a check valve?
 
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