The Tank › Best Advice for a (kinda) new installation.
- November 27, 2010 at 1:44 am #14559
I have done a lot of reading on the forum, and after some debate about the merits, I was over-ruled and we now have a new Hybrid.
I wanted to check in with Larry and the rest of the members on my plan.
The real issue was not having enough hot water for our family. We do not have access to NG or LP without significant installation costs (13K & 5K respectively). The only alternative left was to increase the holding capacity of our electric. I considered getting a Voltex by AO Smith, but at $1000 more than the GE, it didn’t seem worth it. The first hour rating of the Voltex ranges from 70-84 gallons. The GE has a first hour rating of 63 gallons, couple this with the 50 gallons of the old tank, and we have 113 (or so) gallons.
Here is my plan (view the attached pic):
Install a new expansion tank (we currently don’t have one).
Connect the Hot outlet on the new tank to the cold inlet on the old one.
Connect the house supply to the hot outlet of the old tank.
Interconnect the New tank’s cold inlet to the Old tank’s hot outlet via a recirc pump. (I already have the pump.)
The new tank will be wired to 240, the old tank will not be wired.
I will be putting in new anodes in both tanks (I think, do I need a new one in the new tank?)
Both tanks will get a large drain, and the old tank will get a thorough cleaning.
Both tanks will get a new curved dip tube.
Also, I will put in the proper valves to isolate the tanks and want to have the ability to quickly switch back to the old tank (ie, move just the electrical) if the new one fails.
I am considering using the upper thermostat on the old tank to run the recirc pump. The pump could be operated three ways.
1. Run the recirc 24/7 (which seems excessive) at an annual cost of around $25 (we pay 6.75 cents/kWh).
2. Run the recirc on the built in timer and try to guess when to recirculate the water.
3. Wire the hot leg of the recirc pump through the top thermostat on the old tank.
#1 seems like it may put undue stress on the system.
#2 seems like a difficult thing to do and I would likely be lowering the first hour rating of the system.
I don’t know if I can do #3 or not. If the thermostat requires 240 to work, then its a no-go. If it is just a mechanical thermostatic switch, then when the temp is reached, the switch closes, pump turns on, done-deal.
What are your thoughts?
Have I missed anything?
JaetawrightNovember 27, 2010 at 12:47 pm #14560
Hello: You’ve got some interesting thinking going on 😎 Looking at the diagram, are you pumping from left to right? This would be using the heated new tank to heat the old tank, but not recirculate around the house. Also, this way check valves would prevent bypassing when water is drawn. I’m not sure you need two check valves, but isolation valves in the system would be good so either tank could be off line. As to pump control; why not use the lower thermostat if the pump is there only for tank heating? This will keep the whole tank hot. The pump should only run to make up for standby loss, which will be little if everything is well insulated. I see no reason why the thermostat wouldn’t take 120 VAC, but do protect terminals from shorting. I’d avoid options one and two. They will waste energy. If the new tank has a magnesium anode, you can leave it. I’m no fan of aluminum. I would add “too much” insulation to tanks and piping. You’ll have a lot of surface to lose heat from and need to deal with that.
Now, what can be done to make the plumbing system more efficient? Why are you running low on hot water? Do the pipes need insulation? Can you fit in a shower heat exchanger or do cold water washing? Answers to that sort of question might save the need to do all this interesting work 😉
Yours, LarryNovember 27, 2010 at 1:37 pm #14561
Thanks for the reply. You are correct, the recirc pumps from Lt to Rt. Basically the old tank becomes a storage tank, and the pump kicks in to keep the water in the second tank at 130ish. You are also correct about the check valves, they are to prevent cold street water from entering the hot supply side. I thought I would need one on each side of the pump, but after thinking about, one on the hot side of the pump would make sense. I plan on using isolation valves to be able to take a tank out, just didnt put them in the drawing.
I should have mentioned that I already have a recirc pump that keeps the piping hot. It is timed, and works well with our schedule. (When we moved in a few years ago, the 5-8 gallons of wasted water every morning caused me to get the recirc pumps.)
I was going to use the top thermostat due to the fact that the cold inlet is actually hot water from the new heater. My thinking is that after the pump kicked on the entire tank temp would have to rise before the pump turned off. I could run the thermostats in paralel so that if either thermostat was tripped, then the pump would run.
My plan for insulation of piping is to use 3/4 foam pipewrap. Do I need to use fiberglass wrap over that?
As far as the system capacity goes – it is all due to the fact that my wife (and 2 teens) like to take 200 degree showers for 30 minutes. I exagerated the temperature, but not the time. At our old house we had a 50 gallon NG that kept up with the demands, electric is just too slow to recover. Since I cant get LP or NG and I cant make electric recover quicker, the only option left is larger holding capacity.
The pipes are all wrapped well. We have a 50 foot long straight run of 3/4 with approx 10 foot lateral 1/2 runs to the bathrooms and kitchen.
I havent considered a shower heat exchanger, will do some googling on it. A few other questions for you:
Do I need to hook up the T&P on the storage tank?
I was going to put a new anode in the storage tank in case of failure of the new tank. Is there a need for an anode in a tank that is strictly for storage?
How long does it take to get curved dip tubes?
JonNovember 27, 2010 at 11:02 pm #14569
Most of this is more in Larry’s league, but I can answer a couple. You do need an anode in any glass-lined steel tank that has water in it. Odds are it won’t corrode as fast as a storage tank, but it’s still necessary.
How fast you can get curved dip tubes depends on where you are. Where are you?
Randy SchuylerNovember 27, 2010 at 11:48 pm #14570
We are in Washington state, Seattle area to be exact.
The anode I’m replacing is in an A.O. Smith tank. It has the Hex head with the bump, but I read somewhere on your site that all AO Smiths are Al or Al/Zn. It is 4 years old, never been touched since install, so I figured I would replace it.
JonNovember 28, 2010 at 3:45 am #14573
Hello: I like your parallel thermostat control idea as it settles any questions on inlet temp and flow from the heat pump and how that mixes water in the tank. 3/4″ foam insulation is OK. If you decide to thicken it up, try adding another layer of foam with an ID to match the present OD. That avoids any possible wet insulation issues.
Have a look at this: http://www.sunfrost.com/efficient_shower.html for a shower idea. If the long showers are for warming up, it could help. Storage shouldn’t need a T&P as it has no heat source. But, if there is any chance the heat pump could overheat the tank, I’d install a relief valve. Relief valves are cheap 😉
Yours, LarryNovember 28, 2010 at 11:42 am #14574
Then about three days to get you a curved dip tube. As to the anode, it is magnesium. Aluminum/zinc wouldn’t have the bump, and Smith does not, as far as I know, routinely use aluminum/zinc. It’s always a good idea to check an anode, but I think you’re a little early on replacing it.
Randy SchuylerNovember 28, 2010 at 12:22 pm #14576
Thank you both for the replies.
Larry, you should get a little more sleep. 😉
Maybe you still have the energy I had when I was 20ish :dude: and would routinely be up after midnight.
It sounds like you find my plan to be a good one, although a unique one. Based on replies, I dont need an anode for the new tank, and may not need one for the old tank. Wrap the pipes really well, only need one check valve (but several isolation valves). Thermostats can be used to run 120v and run them in parallel.
Randy, sounds like the next step is to take some pictures. I will turn off the hot tank and remove the anode to take a look and post a pic or two. I want to order everything at once, so I will wait for your expert opinion regarding the anode before ordering.
I will also upload pics to this thread once everything is installed in a few weeks.
JonDecember 2, 2010 at 1:33 am #14607
Sorry for it taking some time to get back in here, I had a heck of a time finding the right socket to be able to pull the andoe. It is recessed in the top of the tank, and a standard socket wouldnt fit.
At any rate, I have several picts that I will attach. It does look quite coroded to me, but I am not the expert here. I also though it was interesting that it is only 24 inches long, I was expecting 40ish.
My other concern is that at the top of the anode, there is considerable corosion, about a third of the way in, half-way around the rod.
I know that it looks bad to me, but I don’t look at them everyday. What do you guys think? Is this normal corosion given a 4 year old tank?
Here are the picts:December 2, 2010 at 12:59 pm #14616
No. This anode is just getting started. You’ve got a long way to go before it needs replacing. Actually, it looks as if it passivated for awhile and then started corroding in places. You wouldn’t replace it unless you could see six inches of core wire, per the picture on my Anodes page.
Randy SchuylerDecember 2, 2010 at 1:43 pm #14617
Cool thanks for the advice, I’ll order the dip tubes tonight. It’s a relief to know that it is still good.
My wife was horrified that the hot water tank had something in it that looked so “rusted”. I guess she was thinking that the inside of the tank is pristine. Now I know never to show her the inside of any water pipe (hot or cold) that I replace.:)
JonDecember 4, 2010 at 3:05 pm #14629
Hello: I’m not too thrilled with the look of the anode. It clearly has not worked well in the past. You must have pretty clean water, which slows down the action of the anode. I’d replace it.
Just causing trouble 😎
Yours, LarryDecember 4, 2010 at 4:48 pm #14633
I’m going to play the rebel here. Even if the anode did passivate, it’s obviously working now, and probably won’t passivate again. On the other hand, there is no guarantee a new one won’t do the same.
He’s somewhere in Washington state and could indeed have very good water.
Randy SchuylerDecember 4, 2010 at 5:41 pm #14635
Hello: Go ahead and play Rebel 😛 The exposed area of the magnesium is much less than it would be with a fully functional anode, so I’m concerned that it cannot throw enough current to protect the tank adequately. There is a way to measure it by using a “reference electrode” (look on NACE website) which would prove or disprove our opinions. The only problems with that test are availability and cost.
I have replaced leaking heaters that had passivated rods similar to the one we see. The difference is that at the exposed areas on this rod, there seems to be actual gray metal visible rather than something that’s coated. Hence the debate.
Rebel, meet Trouble 😎
ps. A side benefit of replacement is that Jon’s wife can be un-horrified.December 5, 2010 at 1:06 am #14639
Hey, Trouble! It’s Rebel again! :dude:
Jaetawright, you’ve the ringside seat on a long-running dispute between us about passivation and its causes and remedies.
First, remember that for every water heater out there — and that’s millions — there is a unique scenario and set of circumstances. It’s simply impossible to replicate all of them in a laboratory.
But the lab folks did try to explain passivation. Their theory was that in unusually pure water the cathode/anode reaction wouldn’t start and the anode would sort of “go to sleep.”
Larry also speculated that this could be true in water heaters with Rheem’s resistor anode, which they created to lower the driving current of magnesium to equal aluminum, and get the heater through the warranty period in “aggressive” water.
Great theory, but it doesn’t fly. I HAVE seen anodes in the San Francisco water area, which is unusually pure, passivate. But I’ve seen a passivated anode in one water heater and ten feet away, another that didn’t. Same water, and not especially pure, at that.
Worse, I pulled a bare wire out of a heater once, put a new anode in, came back a year later expecting to find substantial corrosion, and found passivation.
Larry even found one that appeared to be passivated, but when he flaked off the coating, found it was being consumed underneath.
NOBODY understands this issue because there is no pattern.
So my take is that if the anode was passivated but is now working, then leave it. His take is that it’s better to replace it; it might have a jinx on it ( I just got back from the newest Harry Potter film — sorry).
So the choice is yours. And if you want to REALLY gross out your wife, send her into the Basics section and have her look at my old Day and Night demonstration heater shown in The Inside Story.:shock:
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