Sidearm w/o Tempering Valve

[twofer]

I know after reading the title your guys' butts are already puckering but hear me out.

What I would like to do is hook up a sidearm to my electric hot water heater and not hook up a tempering valve so as to not have to redo the near plumbing. My idea in order to keep the installation safe is use a zone valve on the sidearm and set the temperature on the zone to 125° (another temp sensor on my Arduino based control system).

Can you guys think of any problems with a solution like this?

 

[MrEd]

It would probably work under most circumstances, but its not hard to imagine the temp creeping up beyond where it is safe. Zone valves (at least mine) don't turn on and off like a light switch. I personally wouldn't do it - and definitely if I had kids or elderly in the house. If you are going to go to all the trouble, might as well do it right and be safe.

 

[rkusek]

If anything failed on the arduino, wiring to sensor, sensor itself, power to the arduino, zone valve, etc. isn't there a chance of scalding hot water burning someone really bad. I don't think I would ever take that risk. I've even wondered whether a second redundant tempering valve would be a good idea just in case one failed for some reason. I'm probably thinking too much and would hope they are designed well enough to avoid that. But still the reliability of one specialty mechanical item would be much higher than relying on all the components above working properly. I would redo the plumbing.

 

[in hot water]

Why? Is it the cost of the thermostatic valve?

 

[twofer]

If anything failed on the arduino, wiring to sensor, sensor itself, power to the arduino, zone valve, etc. isn't there a chance of scalding hot water burning someone really bad. I don't think I would ever take that risk. I've even wondered whether a second redundant tempering valve would be a good idea just in case one failed for some reason. I'm probably thinking too much and would hope they are designed well enough to avoid that. But still the reliability of one specialty mechanical item would be much higher than relying on all the components above working properly. I would redo the plumbing.

If the wiring or the temperature sensor fails completely then there is no temperature returned to the Arduino. In the programming for the Arduino I have the system check for situations such as this and revert to system default operation in the event that it does happen. The one thing that I would worry about is the temperature sensor failing but still reporting a temperature back and my idea to circumvent this is to use dual sensors. This way if one of the sensors is reporting an incorrect temperature that is within the operational range of temps (my system also checks for the temps to be within an acceptable range) the system will compare the two sensors and use the higher temp of the two sensors, to err on the side of safety. My system already does this for the temperature sensor for the boiler circulator in order to insure that it isn't shut down if one of the sensors is going wonky.

If the Arduino itself failed it would have to fail but still pull power and pull the data pins HIGH in order activate the SSR. I guess it could happen.

Why? Is it the cost of the thermostatic valve?

It's the cost of the thermostatic valve plus the cost to have a plumber come out and install it as I'm not comfortable redoing the plumbing.

 

[kabbott]

Any young kids in the house? If not then go for it but when someone flushes the toilet and you a$$ gets lit up in the shower you will have no one else to
blame but yourself. °F :snake:

Seriously I don't have one and never have but I grew up in a house that had like 180 degree DHW and it's NOT fun when you stick your fingers under the
faucet and some one has just run the hot water.... a tough lesson to learn the hard way. If your sure you can keep it at a reasonable temp then I
don't see it as a huge no no.

 

[stee6043]

I just installed a thermic valve this past summer. It's a 4 beer job with sharkbites. Very easy. You don't need a plumber and the valve itself should cost less than a zone valve....

 

[Gary_602z]

Just do it right! In the long run it will be better and you can rest in peace knowing you have done the right thing.

Gary

 

[Gooserider]

Another problem is that sidearms are not all that great at fast recovery, which is what you'd be setting up to need, since the SA wouldn't come on until the tank temperature was calling for heat. Since any HX also performs worse as the temperature difference gets close, the SA would do particularly poorly at making up the last few degrees before the ZV shuts off...

The secret of the successful SA, is that it is recovering the tank almost constantly, and well before the temp drops to the point where you'd notice... The superheating essentially gives you a bigger usable hot water supply.

This, PLUS all the reasons above, are why I'd agree, do it right and put in the mixing valve...

Gooserider

 

[heaterman]

180* water will cause a third degree burn in around 3-4 seconds IIRC. Treating one of those is a fair amount more expensive than a plumber and a mix valve................just sayin'

 

[kabbott]

Goose has a good point, The main reason my side arm works so well is because it flows any time the boiler is hot and super heats the water in the tank,
otherwise if I only heated to 130-135 I don't think it would keep up.

On a side note what is the view on using temp controlled fixtures( not pressure balanced but actual temperature controlled) for all of the important places instead of
a single tempering valve on the tank itself. The reason I ask is that i have a gravity loop on my DHW for instant hot water at my longer runs. This saves a
lot of water, otherwise the kids will run gallons of water down the drain waiting for it to get hot. If i use a tempering valve I would have to add a pump to the
recirculating loop.(at least i THINK i would have to add a pump) This is the ONLY reason I have not added a tempering valve, otherwise it's a no brainer.

And yes as heaterman says it will take the hide off in seconds at 180...as I said not fun :exclaim:

 

[Tony H]

Just to be safe it's worth it and just think of the legal bill if some visitor to your house gets burnt ... you would be 100% liable because you did not install a device to limit water temp

 

[twofer]

I knew I could count on the Hearth Brain Trust to talk me out of it. Seriously.

You all raise good points so I guess it's time to try to figure out how to put the tempering valve in myself.

I just installed a thermic valve this past summer. It's a 4 beer job with sharkbites. Very easy. You don't need a plumber and the valve itself should cost less than a zone valve....

I know it might seem pretty straight forward but would it be possible for you to outline the process either here or in PM. I assume you cut into the lines and remove the necessary amount of pipe on the hot water side for the mixing valve plus fittings. Then on the cold side remove enough pipe to get the 'T' plus fittings. Is there enough flex in the pipe to do this without having to re-solder? These might be dumb questions but I haven't worked with plumbing before.

 

[stee6043]

If I recall correctly - we used three or four sharkbite 90 degree elbows, two unions, one "t" and less than 12" of pex to complete the job.

Perhaps I can draw something up later but it's really easy. Cut the input and output lines from your heater. You "t" the mixing valve between them with a 90 degree coming from hot and a "t" between cold into the tank and cold "supply". Output from the valve goes to your hot water line runing to the house. Sounds WAY more complicated than it is. If you buy the valve (we used a Taco brand valve) it will come with pretty good instructions....

 

[in hot water]

If you use a valve with a check valve built in, or you add one in the piping, you will need a thermal expansion tank.

hr

 

[mbovee1]

Try the honeywell AMX series (AMX101) automatic thermostatic mixing valve. It has threaded or sweat connections. Cut out a few inches of the hot water line from the top of you hot water tank. Then, It threads directly onto the nipple coming out of the top of your hot water tank. Then, you align the cold port on the valve with the cold supply going into the water tank, cut in a "T", and usually about 8" of pipe to connect. Connect the third side back to the DHW house line. Adjust the hex head dial to the desired max temp and you're safe!

(broken link removed)

I got one from the local HVAC supplier for $100. Peace of mind; priceless.