Hey guys, looking for some input here.

We bought our house in summer 2012. It was built in 1988/1989 time-frame and was built by an electrical contractor. Needless to say the electrical is more than sufficient (dual 200 amp services, one lighting panel, one power panel, 40 breakers per panel) and the plumbing seemed good, being all copper. It was fed by a single 65gal electric water heater with copper hardline run directly to the water heater without a dielectric union (yes, I was shaking my head once I saw that).

Well, I quickly tired of waiting for hot water at the furthest faucet/shower, that being the master bath.

So, after a ton of research and such, I installed a hot water recirculating system, utilizing PEX line for the return line and returns from under the sink in the kitchen (second branch, furthest I could get since I cannot get to the plumbing for the main bath upstairs without tearing into a wall somewhere) as well as a return from just outside the master bath. The return from the master bath is the longest return line and the one from the kitchen sink tees into it about 30ft from the hot water heater.

I used a GRUNDFOS UP10-16BU/ATLC pump which is rated at a max of 3.5gpm.

At around the same time I rebuilt the existing 65gal Bradford-White electric water heater (it was only 6 years old and the tank was in mint shape) with all new 4500watt elements, new thermostats, new T&P valve, new anode and new heat trap inserts after cleaning and flushing the tank. I also added in another Bradford-White 80gal electric water heater (with dual 5500watt elements) having the 65gal feed the 80gal. I also daisy-chained the thermostats so the the top element of the 80gal heats, then the bottom element of the 80gal, then the top element of the 65gal and then the bottom element of the 65gal. I put in flexible stainless lines on all the ins/outs, insulated them and braced the incoming line to prevent vibration. I also went as far as getting the factory Bradford-White paint and repainted the 65gal water heater to look like new.

The re-circulation system returns to the bottom drain valve location of the 65gal heater.

Everything was great for about a year and all of a sudden one day we didn't have hot water. I checked everything and got current being pulled by the top element of the 80gal heater, but no sounds associated with heating water.

I drained everything and pulled the elements. All of the elements had a dark grey "bubble" on the base of the elements. I cleaned it off and it seemed almost copperish. With that I pulled the bottom element of the 65gal heater and noticed copper on the bottom of the glass lined tank.

I put everything back together, filled the hot water system and turned the power back on. Water heated up great.

So, the next step I took was to turn the water temp down from about 140 degrees on the thermostats to about 130 degrees on the 80gal and about 120 degrees on the 65gal heaters. I next turned down the heat setting on the recirculation pump as well as reduced the recirculation time to only a few hours in the morning and afternoon.

It has been about 7 months or so without issues and I am going to drain the system and checkout everything again, but how concerned should I be in regards to the copper in the heater?

I can't imagine with such a low flow pump I would need to add a circuit balance valve on the outlet of the pump, do I? I can only imagine it is wearing on the copper pipes due to velocity? Or could the copper buildup be because of copper that already settled out in the pipes and now had the ability to works it way back down due to higher flow from the re-circulation pump?

For reference in regards to the rest of the system, I did wrap all the hot water and re-circulation piping with insulation, the original plumbing system uses type M copper piping as far as I can see and is in good condition.

I am considering changing the system to either an "on-demand" setup with remote switches by the kitchen sink, laundry sink and master bath to get water up to temp when wanted, or possibly with a flow meter to kick the pump on as soon as someone turns on the hot water if it is not up to temp already. I am going to be running tests tomorrow morning in regards to time required, but still would like an idea on the copper in the water heater.

Any and all input would be appreciated.

Thanks,

Dennis

You have made your system suffer by adjusting the thermostats to fire with the top element first. Water comes through the dip tube to the base of the tank and the bottom element should be doing 95% of the heating in both tanks. If you are getting copper out of the tanks.. you shouldn't be. Do you have hard water? Softener?

I have city water which is amazingly well balanced. A little on the hard side, so I also run a water softener for everything but the drinking water.

The water heaters I have are both top-end glass lined units in great shape.

I do believe the copper is from the hot water recirculation system, either from eroding the pipes or flushing already settled out copper back to the heater.

And, the firing order of the elements are exactly as they are designed from Bradford-White. Top element first, then bottom element. I did not re-engineer that aspect, since it seemed to make the most sense. ie, you want the top element to fire first since it will heat the water that will be at the top quicker, which is also the water that will be pushed out of the heater first as well (thus making the demanded water hotter). When it is done heating that it switches to the lower heater to heat the remainder of the tank, which is doing the majority of the work since cold water settles and hot water rises, thus as it is heating it is constantly mixing upwards. That is just basic thermal dynamics at work.



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ALL electric heaters operate the top element first, and then switch to the bottom. Therefore as long as there is hot water at the top of the tank the bottom element turns on and off as the cold water enters the tank. Your circulation system, as described, is not installed properly. You need balancing valves before the tee where the two lines join, AND a modulating valve between the pump and the tank to limit the flow down to the point where the water just stays hot. I am not sure what you mean when you say there is copper in the tank or how much there is. You may be obsessive compulsive with the wiring to have made them "interdependent", since it would have worked the same way if each unit operated independently, and the entire system would not have depended on the second heater's elements working properly



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As far as a modulating valve, are you referring to a valve acting as a aquastat, or a flow restrictor to reduce the amount of flow through the system? (ie, reduce it even further than the max of 3.5gpm?) The pump has a built in aquastat, built in timer and built in check valve and isolation valve. I already have shutoff valves before/after the pump to facilitate repairs. Couldn't I just use the ball valve after the pump to reduce the flow?

I figured I needed a balancing valve at the tee, but that would not be causing copper in the water heater. I just figured it was something I would be adding when I drained the system for inspection this month. Sorry for not clarifying that part.

And, I wired the heaters in series like that so that I didn't have to run a seperate circuit and timer for the second heater. In running them the way I did I can use a single 30 amp service with a single timer to power both heaters, since at any time only one element will be operating.

Sure, for a customer a plumber doesn't care about requiring another service run for the second heater, but for a homeowner the extra cost and associated hassles for no gain seemed like a silly waste of money. Especially when you can run them in series like I have if you are savvy enough to figure it out.

And yet I don't have any hot water problems at my own house with dual tanks and a recirculation system.. Glad I'm not savvy or my wife would shoot me.

you need something like this to restrict the flow of the recirculating line.
they can be had for alot less than what this on sells for.
they are most commonly used for an internal tankless water heater on a boiler..
[#$%&]

I looked at the curve for that circ, and I doubt it is a velocity problem.Copper doesn't oxidize "dark gray" either.Dark gray sounds like anode material.



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Paul48, thanks for confirming what I came up with as well... The pump I choose was well below the "curve" of having issues regarding velocity...

Now, did I do the advanced calcs to "be sure", no, I guesstimated... But considering that fact that the run is at least 80ft of 3/4" with about 12 tees and 90 degree fittings in there by teh time it hits the recirculation loop on the big loop and about 50 feet and 1/3 of those fittings on the second, smaller loop I figured if anything the pump was "undersized" for the application. Which is just fine with me as I want to prevent as many potential long-term issues as possible.

I tested things just now after having sat all night and it takes approx 2.5 minutes to get hot water to the master suite if I do an on-demand hot water setup. A wait that long kills the whole premise of a hot water recirculation setup.

In the meanwhile I am back to the timer setup with the aquastat set to about 10 degrees below my thermostat temp and the ball valve directly after the pump cut to half. I'll give it a couple days to see how things work out temp-wise.