DHW mixing valve and check valve requirements?

markt

One DHW mixing valve installation instructions say a check valves are required, another says "if local code requires check valves", another doesn't say...



Is there something about a DHW mixing valve that triggers need for check valves?



Currently I have no check valves, and no expansion tank, in my entire potable system. Nor do I have a pressure regulator (city pressure is 55psi.) I do have a water tank relief valve.



So if I add a DHW mixing valve (and raise tank temp to 140-150), do I need check valves or anything else?

Zman

Check

The only check you have to install now are to protect against hot-cold, cold-hot cross connect. Some mixing valves have them built in.

The other check valves are an entirely different subject.

Carl

hot_rod

does it have

a recirc piping and pump? If so the use and installation of checks becomes important.

markt

no recirc

Here's a pic from Caleffi mixing valve install manual for non-recirc system. Any idea why they show check valves (and expansion tank.)

Charlie from wmass

They show check vales to

prevent the hot cold water cross flow that was mentioned above. They also show a pressure reducing valve which is why they have the expansion tank in the diagram. The way they show it is the best way to do it when the incoming pressure is high, I figure above 75 psi. The budget does not always allow ffor the expansion tank, and it is not needed unless the expanding water can not relieve  upstream of the tank. The check valves at the valve are required if the valve is installed in MA. I can not speak for other areas.  

markt

OK, I get the expansion tank

but what's the problem with a little hot/cold cross flow? Some other manufacturer's install instructions, Taco for example, show no check valves.

Zman

Check

Mark,

Some manufactures put integral check valves in the mixer. No need for another in that case.

Is long as the owner is OK with a little hot in the cold and cold in the hot, don't worry about it. I have found people have this crazy notion that when you turn the hot handle you get hot water and when you turn the cold handle you get cold. The other thing they like is once you set the temp to the shower it stays at that temp. They just don't like it if gets scalding hot when the washing machine downstairs turns on.

Seriously, if you don't have check valves, slight pressure differences in your system will cause cross flows that will annoy the owner and then, in turn, you.

Carl

SWEI

Internal Checks

http://www.symmons.com/Commercial-Products/TempControl/Symmons-TempControl-Thermostatic-Mixing-Valve-6-400.aspx

hot_rod

with or without checks

is how the Caleffi valves are offered.



Other manufacturers may include the checks, or show a thermal drop in the piping, in their installation manual. Adding the check, of course adds cost and some pressure drop, but does allow more accurate control as Carl mentioned.

hot_rod

another suggestion

All thermostatic valve will require maintenance and cleaning from time to time.



How often depends on how hard your water is and how much you run thru the valve.



The hotter you run your DHW tank, the more it precipitates minerals from the water and they end up where???



So install the valve with some isolation valves so it can be removed, disassembled and soaked in vinegar or de-limer from time to time.



There are a number of different ASSE listings for thermostatic valves. Actually a confusing amount of listings that change often The last 4 digits is the year the listing was amended for example ASSE 1070- 2003. AHJs can accept different listings in the code.last changed A valve used for distribution is a ASSE 1017.



A valve used at then point of use or shower, sink, etc is a ASSE 1070. This valve is limited to 120F operation and has some other different operating criteria.



Valves may also have multiple listings.



AND of course the Low Lead IAMPO listing may be required in your state and will be nationwide in 2014.