Mixing valve for domestic hot water

JoeKansas

I'm having trouble with my domestic hot water system.

I've got a SuperStor indirect 40 gallon tank that I heat with an outside wood fired boiler. Water temp gets up to nearly 160° in the tank.

I plumbed a Watts model 70A tempering valve into the system, just like they showed in the manual illustration.

I can't get the water temperature down to comfortable levels.... sometimes it gets up to 140°+ as shown by a thermometer put in the water stream from kitchen sink.

One thing I wonder about... check valves. The heat from the water in the tank transfers out to the cold water supply.. so the "cold" water feed to the valve is just as hot as the water it's supposed to be tempering. Should I put some check valves in the plumbing to 'insulate' the cold from the hot.. I'm afraid it's confusing the tempering valve and not letting it work properly

.

lchmb

impressive....

Jean-David Beyer

It looks as though you no connection the discharge outlet of the P/T valve. I believe that code does not allow that. (N.B.: I am not a heating professional).

I do not know your tempering valve, so I do not know the minimum flow rate where it will regulate. An oversize valve will do you no favors.

I have a Caleffi valve on mine that will go down to 1/2 gallon per minute. When I was looking for a valve, most of them would go down only to one gallon per minute. My valve has a check valve on both the hot and the cold input. I have added a well for a thermometer on both the hot input and the mixed output to make setting it easier.

hot_rod

More accurately that is called a hot water "extender". Watts website shows it to be a discontinued product? Even the low lead version.

I don't think it ever had the appropriate ASSE listings as a protection device.

If safety for your family and guests is a concern look for a ASSE 1017 device at the tank, maybe a ASSE 1070 as a point of use device.

Best to pipe them with a thermal drop, or add the optional checks to prevent pressure induced cross over.

JoeKansas

Well, I ordered a Caleffi for use at the tank, with gauge and check valves... I'll see how that does.
Thanks HotRod...

JoeKansas

Should have bought one of these in the first place. Works like a charm, and much easier to plumb.
Bought the check valve variety... no heat creeping out into the water lines...

IndependentEddie

My question relates to Mixing Valves but with the reverse scenario. I just had a 60 Gal Superstore Ultra installed with the optional mixing valve. I don't believe that either Gas or Electric fired water heaters need them. My question is optimizing efficiency. We got the bigger tank because with the in-line furnace heater we used to have you could never fill a tub with hot water. Although only two of us live in the house it is a 4-5 bedroom with 3 full baths and I thought for resale value having a big tank would be desirable for resale. It doesn't seem to make sense to heat the tank to 140 degrees, then use the mixing valve to mix in cold to drop down to 115-120 and then again at the tub or sink mix cold again to get to "consumption temperature" of less than 100. This makes sense to me if you need massive amounts of water to supply so that 60 gallons of 140 degree water would probably supply 100 gallons of less than 100 degree water. For us, I would think that the most energy efficient settings would be to set the water temperature for the tank to 120 degrees or so and set the mixing valve to maximum (no cold water). This would supply 60 gallons of 120 degree water which when diluted with cold at the sink or tub would be more than we would ever need. Lowering it even more might make sense. We never wash clothes with hot water and the dishwasher has a heating coil to increase the temperature. Anybody have experiences with this?

Zman

The advantage of the mixing valve is that it helps prevent scalding as the temp in the tank will typically fluctuate due to the location of the sensor and the natural stratification that will happen in your tank.

Legionella and other bacteria's thrive in the lower water temps you are considering. Raising the water temp in the tank will decrease these risks significantly.

If neither of these are a concern to you, the setup you are considering should work just fine.

j a_2

> @Zman said:
> The advantage of the mixing valve is that it helps prevent scalding as the temp in the tank will typically fluctuate due to the location of the sensor and the natural stratification that will happen in your tank.
>
> Legionella and other bacteria's thrive in the lower water temps you are considering. Raising the water temp in the tank will decrease these risks significantly.
>
> If neither of these are a concern to you, the setup you are considering should work just f


Zman I totally agree with you. Great points..120 to 130.... degrees....
..

JohnNY

The use of mixing or tempering devices is mandated by Plumbing Code in New York City any time domestic water is heated by an "H"-stamped boiler or water heater, or any time storage temps do by design or could potentially exceed 140°f.

That Figure 4 drawing in the original post is absolute crap.
The relief valve has a probe that has to sit in the tank, not extend well past the jacket with a tee in-between, no less.
We use thermal loops to stabilize our temperatures, except in a case where a constant recirculating system is present.