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Water heater tempering valves


Richard Moore
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I had a new home today. The water heater was a fairly basic 40 gallon American ProLine (with Flame Guard) and served only the potable water. It was plumbed with a tempering valve directly above it. No harm in having one but I don't believe I've seen one before unless the water heater also served hydronic heat.

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I took a look at the on-line install manual and found this...

3. The manufacturer of this water heater recommends

installing a tempering valve or an anti-scald device

in the domestic hot water line as shown in Figure

14. These valves reduce the point-of-use

temperature of the water by mixing cold and hot

water and are readily available for use.

Out of curiosity I also took a look at a Rheem manual and found this...

Notice: Mixing valves are available for reducing point of

use water temperature by mixing hot and cold water in

branch water lines. Contact a licensed plumber or the

local plumbing authority for further information.

Not a "requirement" in either case, but I was wondering if youse guys are starting to see these installed?

I have mixed feelings about them in this application. On one hand it is an added safeguard against scalding but, on the other, it could mask a developing problem with the water heater thermostat.

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Originally posted by mwfigg

Is that a cold line coming down to the top of the tempering valve? It looks as though the installer just cut the valve into the hot line which wouldn't serve any purpose

Of course it's a cold water line and of course it serves a purpose. That's how those things work - they allow cold water to mix with the hot water coming out of the water heater until the water temperature is reduced to the target temp.

I see them occasionally, Rich. Did you happen to check the Btu/Hr rating on the tank? I normally see them when the w/h is one of those 65,000 Btu/Hr high performance tanks versus the typical 40,000 Btu/Hr tank.

ONE TEAM - ONE FIGHT!!!

Mike

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Just a regular 40,000, Mike.

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"Does the manufacturer allow the plastic tpr extension pipe and pipe insulation to be that close to the draft hood and vent connector?"

The CPVC doesn't start until that first elbow and the insulation clearance also looked fine to me. Too many elbows when you include the two that had to be in that outside wall and the final one at the discharge termination itself, but it was a very short run. Although the home was new, it was now bank-owned and being sold as-is. I made the executive decision that it was safer to leave it that way than have the client really screw it up trying to change it.

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I have only seen these on Type 1 or Commercial construction, where the supply is from a boiler and the supply is hotter than 140 degrees. If this is on a standard water heater the mixing valve must be set to minimal pressure on the thermo plunger.

It will eventually stop functioning since there is no travel in the thermo plunger.

It should not be a help or a problem simply useless.

I would be more concerned about the PVC pipe coming off the TPR valve, the pipe will probably fail if ever used.

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Originally posted by Rocon

I have only seen these on Type 1 or Commercial construction, where the supply is from a boiler and the supply is hotter than 140 degrees. If this is on a standard water heater the mixing valve must be set to minimal pressure on the thermo plunger.

It will eventually stop functioning since there is no travel in the thermo plunger.

That's interesting 'cuz I've seen them outlast water heaters two times over here.
It should not be a help or a problem simply useless.
Not been my experience here. They were doing what they were supposed to; regulating the temperature of the hot water going to the fixtures.

I would be more concerned about the PVC pipe coming off the TPR valve, the pipe will probably fail if ever used.
As Rich said, it's CPVC and the discharge pipe is metal up to that point. I disagree, I don't think it will "fail" at all. In the event that the TPR valve discharges it might get soft and flex some but it's in drainage plane and he says that it's constrained by the wall and framing so I expect that it'll just get soft. I think he made the right call.

You say tomayto I say tomahto.

ONE TEAM - ONE FIGHT!!!

Mike

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Originally posted by Jeremy

Seems unnecessary to me. Maybe a phobia about bacteria? Turn the water heater to highest setting to keep tank clear of bacteria and then temper back to safe temperature. Just a thought...

I think that's it.

It's the conflict between protecting folks from Legionnaires. You need really hot water to kill the bacteria but really hot water also scalds, obviously.

That's a simple, effective solution to accomodate both. Wow, sometimes simples solutions are right in front of my eyes!

I'm assuming the stat was cranked to it's highest level?

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"I'm assuming the stat was cranked to it's highest level?"

No, and there's no suggestion in the instructions to do anything like that. It seems to me that the "recommendations" for tempering valves are to ADD another anti-scalding device, not to substitute one for the other and then rely only on that unknown "after-market" device. While it might be a good idea(?), I think I would want the water heater manufacturers to include, and be responsible for, the valve before I would be comfortable with cranking the thermostat to its highest as a regular practice.

In my case the thermostat was at its normal factory mark, but I was initially only measuring around 95°F. I had to turn the tempering valve up to determine the actual tank temp was 115°F and that the tempering valve was set low.

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