# Pressure balanced Faucets and Tankless water heaters



## Smitten_kitten (Sep 8, 2011)

Ok in the State of Mass were i live and probably everywhere in the U.S. All Shower Valves ETC are required to be Pressure ballanced or thermostatically controlled. 

Now Pressure balanced is the most common. As known in order for a pressure ballancing spool to work properly the pressure on both the hot and cold must be equal.
Now this question is purley theoretical i have never seen this happen before but i don't have too much experiance either... 
Today you often see tankless water heaters all over. They are very much in style especially were i live/work. However they are built with internal Flow restrictions. Some restrict the flow even more to better heat the incoming water as the water heater tries to hit its set point temp. Thus lowering the outlet pressure even more . During the Cold Winters we have in Mass. this flow restriction could get worse when the ambient temp. of the water is coming in even colder causing the flow to be reduced further in order to transfer more heat to the water to maintain the outlet set point temp. 

Now my question is this- Can this pressure reduction from these tankless heaters be enough to cause the balancing spool of say a shower to close due to the unequal hot and cold pressure?? Thus in theory one could turn on a shower and No water comes out???


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## Gettinit (May 9, 2012)

As long as there is flow through the hot and cold on mixing valves and pressure balancing valves it will flow water. Obviously it will not be adequate if it were almost valved off but it will still let water flow. It is only when the water is off will most valves not let water flow through at all.


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## Smitten_kitten (Sep 8, 2011)

thanks gettinit, so this is not really a common occurance. Thats why i like the eternal Tankless water heaters their full port no restriction.


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## Wayneswilson (Jul 28, 2012)

Smitten_kitten said:


> Ok in the State of Mass were i live and probably everywhere in the U.S. All Shower Valves ETC are required to be Pressure ballanced or thermostatically controlled.
> 
> Now Pressure balanced is the most common. As known in order for a pressure ballancing spool to work properly the pressure on both the hot and cold must be equal.
> Now this question is purley theoretical i have never seen this happen before but i don't have too much experiance either...
> ...


If properly sized for the lowest flow rate on the tempature rise chart for any tankless water heater while it may require more units, the flow will be great. For a fifty degree rise here in Texas in the winter one unit can do the entire home. With northern tempatures being lower, the same Rinnai unit that I use here would only provide a 3 gpm or so flow rate, thus being out of code. We have to size the heating capacity with flow rate for the lower tempature months to ensure proper hot water capacity as stated by the code. So while theoretically it could be possible if the units are installed to the code it should never be a problem. All states are different so I am not sure how it would work where you are, but I have had to use to 7.5gpm tankless units to deliver 6gpm of hot water needed in the winter months up in northern Texas.


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## Plumbus (Aug 4, 2008)

Sorry, posted to the wrong thread.


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