Expansion Tank question

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Old 08-25-17, 08:18 PM
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Expansion Tank question

Why is an expansion tank recommended/required if your water heater has already has a relief valve in case of pressure build-up?


Recently had a water heater installed in a 60's-era house and was told the tank was not necessary.

Also: Are the anodized rods not needed anymore? My new heater does not have one.



* To the moderators, not liking the new format.
 
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Old 08-25-17, 10:02 PM
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* To the moderators, not liking the new format.
To the member... neither are the mods. It's not our choice.

As the water is heated it expands. Normally the pressure would build up and ultimately expand back out the water main. With many homes using a PRV (pressure reducing valve) the valve will not allow any pressure to go back out. This increase could cause higher pressure within the house. The combination of a small pressure tank and check valve (if no PRV) absorbs the increased pressure.

The anode can be part of the hot water pipe.
 
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Old 08-26-17, 07:10 AM
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Often times inspectors won't require an expansion tank in the older houses if no check valve is present on the main line. It never hurts to have one though.

What I don't understand is why my state now requires the expansion tank on tannkless water heaters.
 
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Old 08-26-17, 11:08 AM
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What I don't understand is why my state now requires the expansion tank on tannkless water heaters.
If they are usually over 50-75k btus they are required... Cant remember the exact # without referencing code book..
 
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