adding mixing valve and expansion tank to conventional electric water heater

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RustyShackleford

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I want to add to my water heater an expansion tank (house has closed plumbing system) and a mixing (aka. tempering) valve, so that the temperature can be set at 160-degrees or so for add'l hot water capacity.

The water heater is in the basement, and currently both the cold and hot connections are soldered 3/4" rigid copper pipe going straight up from the tank connections into the two living floors of the house (with a shutoff valve on the cold inlet pipe).
I'm thinking of adding the expansion tank and mixing valve as shown here.

Screen Shot 2022-10-20 at 3.56.24 PM.png

The black squiggly thing is a flexible water-heater connector.

Wondering about the positioning of the two devices.

1. Is it ok for the expansion tank to be on its side (as shown) and is it ok for it to be completely above the water heater ? Searching, it's often shown hanging off the side of the cold-water line, so the opening is pointed upwards and the whole thing is below the top of the water heater.

I'm guessing this drawing (from the install instructions) says it's ok. It shows the tank optionally both sideways and completely above the water heater (though not both at the same time).

Screen Shot 2022-10-20 at 4.16.38 PM.png

2. Is it ok for the mixing valve to be oriented as shown (with the outlet pointed upwards) ? The instruction sheet for the one I've purchased (https://digitalassets.resideo.com/damroot/Original/10014/62-3075EFS.pdf) is really confusing. The paragraph on the lower-right of the first page says "can be installed in any position consistent with the intended use" but then "for domestic hot water supply, the valve must be installed as shown in Fig. 1" and Fig.1 shows the thing oriented wit the outlet pointing sideways and the hot and cold coming in from the bottom and top (it's also showing a recirculation system, which I don't have).

I guess the reason my positioning of the components is so different from the various instructions is that I have the cold and hot lines coming in from directly above the water heater.
 

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Only suggestion I can make is utilize something more than the copper piping to support the tank ( search expansion tank straps ) . If & when the bladder fails in the tank ..... they become heavy with the water weight.
 
sarg said:
Only suggestion I can make is utilize something more than the copper piping to support the tank ( search expansion tank straps ) . If & when the bladder fails in the tank ..... they become heavy with the water weight.
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Yes, for sure. Can probably mostly use a block of wood on the top of the water heater, cradling the side of the expansion tank
 
Geofd said:
Are you not getting enough hot water why do you think you need an expansion tank????
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My understanding is that the expansion tank is to prevent excess pressure in the house's plumbing system, which can cause damage to components after awhile (I've heard it compared to high blood pressure in your body); the house is on town water, with a check valve, so it's a closed system with nothing to absorb pressure spikes.

Maybe you meant to ask why I think I need a mixing valve ? This is for a vacation house, and it's a 50gal unit in a house with 4 bedrooms and 3 bathrooms. I know my wife and I sometimes exhaust the 50gal unit in our main home. So with perhaps as many as 8 people in the vacation house (renters or a family reunion) I really think 50gal is not enough (not set at 120-degrees anyhow, which I think is important for safety, especially with kids present).
 
Unless the tub shower valves have hot water limit devices That can be set I would not run a rental house at 160 degrees with a mixing valve.

I don’t like the idea of running tanks that hot period. Water above 140 changes the game.
 
Twowaxhack said:
Unless the tub shower valves have hot water limit devices That can be set I would not run a rental house at 160 degrees with a mixing valve.

I don’t like the idea of running tanks that hot period. Water above 140 changes the game.
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Failure mode where they let straight hot water flow ? They're claiming pretty hard that this wouldn't happen - even mention using it in nursing homes ..

Also, water heater itself is in a basement that renters will not have access to.

Screen Shot 2022-10-20 at 10.58.16 PM.png

Ah well, even if I don't run the water heater above 140, it's still 1/3 again as much usable hot water, right, assuming incoming cold is 60 ? Since (140-60)/(120-60) = 1.33 ...
 
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With 120 degree hot water and 60 degree incoming cold water a 105 degree shower would require 76% hot water. So you if your shower head runs 3gpm 76% of that 3gpm will be hot water.

With 140 degree hot water 56% of the shower will be hot water.

A gas tankless would be ideal if possible.
 
Rheem makes an electric hot water extender. It boosts the outlet temp and doesn’t require another electrical circuit if the water heater is electric.

I’ve never used one. I’ve read about them.

Or go with your idea of the high temp setting and extender. Although personally I don’t recommend
 
Twowaxhack said:
Rheem makes an electric hot water extender. It boosts the outlet temp and doesn’t require another electrical circuit if the water heater is electric.
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I'm not sure how that helps. Do I set the water heater to 120 and then the booster bumps it to 140, so occupants mix in more cold water at the point-of-use ? That seems more dangerous than 140 in the tank which is mixed down to 120 before it ever gets near a shower.
 
RustyShackleford said:
I'm not sure how that helps. Do I set the water heater to 120 and then the booster bumps it to 140, so occupants mix in more cold water at the point-of-use ? That seems more dangerous than 140 in the tank which is mixed down to 120 before it ever gets near a shower.
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Google it and read about it.

Do what you’d like. I’m only making suggestions.
 
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My experience with mixing valves (admittedly 30 years out of date) is that at very low flow rates and if there’s any convection available, they will allow hot water at the full tank temperature into the lines.

I like the concept, and it really sounds like you need a solution, so if it’s not expensive I’d give it a try, but just be wareful and have a Plan B.
 
You also gottA remember when it starts to fail who's gonna fix it and now you either have to live with over shooting/undershooting domestic water were I work we try to go right out of the tank with the desired temp Ang mix down at the showers, and we're we do have mixing valves it can be constant maintenance because of water quality
 
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Geofd said:
You also gottA remember when it starts to fail who's gonna fix it and now you either have to live with over shooting/undershooting domestic water were I work we try to go right out of the tank with the desired temp Ang mix down at the showers, and we're we do have mixing valves it can be constant maintenance because of water quality
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Constant maintenance ? So they're failure prone ? Or do you mean the water quaility is bad there and clogs it up ?
 
Geofd said:
The calcium builds up on parts wether it's a bimetallic coil or a cartridge we soak them in vinegar and we have an ultrasonic cleaner
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Ok, well seems to be very low mineral content in this water, so hopefully not too bad a problem.

What does the valve do when the calcium builds up ? Pass pure-hot thru, or what ?
 
It can go either way we also have replacement parts ready to go so the other parts can be cleaned it's best to make your system simple and safe let your shower valves mix down and research your local code to see what your max temp is like twowax says take the risk out of it
 
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RustyShackleford said:
Ok, well seems to be very low mineral content in this water, so hopefully not too bad a problem.

What does the valve do when the calcium builds up ? Pass pure-hot thru, or what ?
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Wait until you heat that water above 140. Above 140 and the game changes. Do your research.
 
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