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 Water Heater vacuum relief valve
Author: pbr2424 (NH)

When the plumbing code say a vacuum relief valve should be installed on all hot water storage devices such as a electric hot water heater it doesn't specify which type. There are the atmospheric vacuum breakers and the pressure vacuum breakers. It seem most hot water heater have the atmospheric vacuum breaker but the system is under continuous pressure so shouln't there be a pressure vacuum breaker. Where am I confused.

Thanks.

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 Re: Water Heater vacuum relief valve
Author: LemonPlumber (FL)

The only one in our code would be vacuum relief type.Meant to break the vacuum on the cold side to keep the heater /point of use type \from being siphoned dry...All top feed heaters would not be applied or subject to this code.

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 Re: Water Heater vacuum relief valve
Author: pbr2424 (NH)

Where I am at persons install a vacuum breaker 6 inches or better on the cold feed to the top of an electric hot water heater tank but it's usually an atmosphic breaker. But the line is under constant pressure not like a sillcock so in theory should it be a pressure breaker.

Thanks

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 Re: Water Heater vacuum relief valve
Author: rjones0281 (MO)

there is no such thing as a pressure vacuum breaker on a hot water heater but is really a contradiction in terms.
pressure and vacuum are too different animals.
pressure is pushing air or water out.
and vacuum is pulling water or air in.
unless you consider an expansion tank (kind of like a two way open valve)
i have never seen a water heater that will pull or vacuum water or air in to the tank every thing is under pressure.
i simply ask where is the vacuum.
in the scald tube???
there are some industrial applications that employ two way pressure valves.
but not on a hot water heater.



Edited 2 times.

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 Re: Water Heater vacuum relief valve
Author: LemonPlumber (FL)

Rj bottom feed heater installed in a ceiling above .Water supply is cut off. vacuum is created by fixtures that are open below the heater.Vacuum relief.It is often afailure of many non plumbers here.

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 Re: Water Heater vacuum relief valve
Author: pbr2424 (NH)

I was looking at Watts backflow preventers FAQ and got to thinking about atmospheric breakers and continous pressure. I got to think of something esle to do.

Thanks

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 Re: Water Heater vacuum relief valve
Author: LemonPlumber (FL)

n36 n360...Check at www.watts regulator.com.These both mount above the heater so supply line run is important .but are inexpensive and preform to code requirements.

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 Re: Water Heater vacuum relief valve
Author: pbr2424 (NH)

That is what is used around here. Glad you found were it specifies were it can be applied. Thats what I was mentioning but never saw the exact specifications before just assumed it was ok. Leave well enough alone.

Thanks



Edited 1 times.

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 Re: Water Heater vacuum relief valve
Author: LemonPlumber (FL)

You do know that a spring check in the line before this a v will stop it from failing?In some cases where water shut down occurs often .

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 Re: Water Heater vacuum relief valve
Author: pbr2424 (NH)

No but that makes sense but then you would have a closed system and need an expansion tank. Another can of worms.

Thanks

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 Re: Water Heater vacuum relief valve
Author: hj (AZ)

You are confused because you are thinking of the wrong type of valve. A vaccum relief valve is NOT a vacuum breaker valve. It is a valve similar to a T&P valve which opens when there is a vacuum in the system. Here, they are required on roof top solar systems, but not on water heaters because we have very few that meet the installation requirements that dictate one.

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 Re: Water Heater vacuum relief valve
Author: pbr2424 (NH)

Thanks for your response. You cleared up my confusion and I understand what you are saying. I think some people might say vacuum breaker when they mean vacuum relief or I might of. I will remember the difference

Thanks

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 Re: Water Heater vacuum relief valve
Author: hj (AZ)

You are getting confused. A vacuum "breaker" prevents vacuum from forming. A vacuum "relief" valve eliminates it when it forms. An elevated heater, such as in an attic or upper level, can be subjected to a vacuum if the water supply to the building is turned off and the water piping is drained. The amount of vacuum is directly proportional to the height of the tank above the point where the water is being drained, but because of the amount of surface on the tank, even a slight vacuum can exert tremendous pressure on it, and under the right conditions the tank can collapse. I suppose you have never seen a picture of a gasoline or water tanker which had the valves turned on before the vents were opened. Or the water tower in Texas which looked like a crumpled paper cup when the same thing happened to it.

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 Re: Water Heater vacuum relief valve
Author: hj (AZ)

ANY check valve will prevent, or minimize a vacuum caused by opening a cold water faucet, but a hot water faucet will create the same negative pressure, unless there is a vacuum relief valve on the tank.

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 Re: Water Heater vacuum relief valve
Author: m & m (MD)

Rheem requires a vacuum relief on its "Marathon" water heaters because they are made of a composite 'plastic' material. If they are subjected to vacuum, they will implode. I have seen it happen.

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 Re: Water Heater vacuum relief valve
Author: Shoemaker2 (MA)

When there is a loss in pressure due to a line break, or when a fire engine is sucking on a hydrant a water heater could collapse if no breaker is in line.

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