2 water heaters, series or parallel??

macingraceDecember 6, 2012

The whole story as short as I can make it. Currently 1 40 gallon electric water heater. I am replacing with a 50 gallon gas. When this is done I want to put a electric 40 gallon in master bath I got for $30 brand new. I will use existing circuit to power it. What I want to accomplish:

MB is about 90 feet away from water heater. With circulating pump installed takes about 1 to 2 minutes for hot water to hit bathroom. Without pump it can take up to 4 or 5 minutes. I have no issues of running out of hot water. I just want to set up 2 water heaters so I can remove pump and get hot water faster to MB. I also want to do this the most efficient way possible.

My thought is to supply MB (2nd) water heater with the hot side from the 1st water heater and this will save me money not having to have the electric heat as much water. The first will supply the rest of the house as they are all within 10ft and only as far away 25 feet of 1st water heater. I believe the circulating pump in my case is costing me lots of electricity. I am just looking to get hot water to my MB quickly and saving money on utilities. If I supply cold water to MB it would seem to me this is more expensive as I have a gas WH heating cold water and the electric doing the same.

Any thoughts on this? Anything else I need to know to do this correctly??

Thanks for your help.

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I guess the only thing I would say is that using a 40gl heater for just one bathroom seems like overkill. Unless you take a lot of tub baths...

And yes, you can put them in series.

And while they are sitting there, they are both heating 'cold' water. If it were me (and others will probably state I'm wrong), I would put a wall switch or timer on the electrical unit so that it is only on when it is needed. That is, it comes on when you turn on the light switch or at certain times of day (morning/evening).

    Bookmark   December 6, 2012 at 4:40PM
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Based upon the information you have presented you don't need another water heater, you need to get your circulator pump working correctly.

You stated that the run from the water heater to the bathroom is 90'.

Assuming the 90ft trunk line is 3/4", with a flow of only 1gpm the velocity of flow would be 0.49ft/sec so even without a pump, if you were to turn the hot water on at the lavatory the delay should only be about 180 seconds.

If the pump is installed correctly there should be a return line from the far end of the trunk line back to the water heater, and the trunk line should remain hot at all times. The only delay then would be the short branch line from the trunk to the fixture, which would normally be under 10ft and that would generally be a 1/2" line.

At a demand of 1gpm the velocity of flow in a 1/2" line is 0.84ft/sec so for the 10ft line the delay should be about 11.9 seconds.

Now if you were to turn the shower on, the demand is approximately double that of the lavatory and the delay times would be one half of what they are to the lavatory.

If the circulator pump is installed correctly it should have an aquastat that senses the temp of the return line and only turns the pump on when the return line temp drops below a set point. The pump then only runs long enough to replace all the water in the trunk line with hot water.

A 3/4" line holds 1 gallon for every 43' of physical length so when your pump runs it should only have to pump a bit over 2gal and if the lines are insulated per code, that should only happen about 3 times per hour in winter and twice per hour in summer.

The circulator pumps are typically a125v 0.74A (85watts) 1/24hp pump and they produce a 2gpm flow into a 1/2" return line, which means your pump should run about one mintute on each cycle, and assuming the worst case of 3 cycles per hour, the pump would run 3 minutes per hour, so the total electrical cost would then be 3mins x 85watts equals 255wats per hour, which is about 1/4 of a Kw/hr, which is nationally averaged at $0.12. That means you would be paying the rediculously high sum of $.03 per hour for instant hot water.

Now ask yourself how many hours that pump will have to run to offset the cost of installing and operating another water heater?

    Bookmark   December 8, 2012 at 4:41AM
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Lazypup, I think your math or your words are off a bit.

To get 255 watt hours from an 85 watt device, that would be three hours of operation.

Your example is running 85 watts for 3 minutes an hour, so that's 85 * 3/60, about 4.25 watt hours per hour. 100 watt hours per day, 3 kilowatts per month (36 cents at your pricing assumption). Although, running a circulating loop does increase heat loss so there'd be more energy consumed by the water heater.

    Bookmark   December 8, 2012 at 1:23PM
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The circulating pump is connected to the faucet under the sink in the MB. This was done per instructions with pump. It is set to come on and off 3 time zones a day, early mid and late.
What would be a better way to install. As stated all connections are made right under the sink as the instructions told me too.
I do have access to all plumbing in crawl space.

    Bookmark   December 9, 2012 at 3:18AM
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You are correct, the actual electrical utility cost of operating a residential circulator should be in the order of $0.36 to $0.50 per month.

Now it can be argued that the loop would increase heat loss in the water heater, but that is not always true either. Consider the facts. Code maximum for domestic potable hot water distribution is 125degF so we set the circulator to come on when the water temp drops to about 100degF and off when it reaches 120degF.

The amount of water being moved is very neglible, by example in the system at hand the line is 90' long and assuming it is a 3/4" line, that would be a total of slightly over 2gal. (3/4" pipe = 43.4ft/gal).

The water in the return line would then be entering the water heater at approximately room temp, and by the time that little 2gal mixes into the 125degF water stored in the tank, it is doubtful if the resultant temperature drop would be enough to trigger the water heater burner to start.

On the other hand, if we have a system with no circulator every time they desire hot water they have to begin by running two gallon of water down the drain while they wait for the hot to arrive. We then have the cost of the two gallons of wasted water, plus the two gallons entering the tank to replace it is coming directly from the cold water supply at 36 to 50degF so in fact, the circulator actually will conserve water consumption & reduce the water heater firing time.


Can you post the make & model of your pump so I can check the installation & operating instructions? I think the answer to your problem is very simple, but I would like to check out how your pump is controlled before I offer the solution.

    Bookmark   December 9, 2012 at 5:44AM
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Sounds like the OP may have a retrofit recirc pump installed under the sink in the MB instead of the traditional recirc pump with dedicated return line that lazypup is describing.

Pup is right questioning the setup or operation if it is a traditional recirc setup cause hot water should be right there all the time..

If it is a retrofit recirc pump then 2 minutes is taking a very long time. My retrofit recirc, which is about as far from the WH as the OP's MB is, only takes seconds for hot water to arrive.

Would help lots if the OP listed what pump and how it is installed.

    Bookmark   December 9, 2012 at 3:54PM
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Thanks everyone for taking an interest to help. It took me several hours to find, but the circ pump is a Laing AutoCirc Pump, mad by Laing Thermotech, Inc.
I have also added a picture of the circ pump under the sink in my MB. I hope this helps in some way.

Thanks again

    Bookmark   December 10, 2012 at 1:57PM
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Same pump I've had for years and it works great. If it takes two minutes for hot water at that hot faucet then something is wrong or not operating correctly.
Triple check that you made the connections correctly cause it is easy to get confused.

Here is a link to the instructions... http://www.jupiterheating.com/pdfs/laing-autocirc-valve-IM-01.pdf

If everything is hooked up correctly then you might have a problem in the valve that is on top of the pump. Contact Laing support to see what they say.

    Bookmark   December 10, 2012 at 2:57PM
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I'm not too brite, but where is the electrical hookup for that pump?

    Bookmark   December 10, 2012 at 5:13PM
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I'd always heard that it wasn't a good idea to ingest (either drink or cook with) water that had run through a water heater. Something about higher dissolved minerals and bacteria potential, both of which were best avoided.

That pump pulls the lukewarm water out of the hot pipe and puts it into the cold lines. No thanks.

    Bookmark   December 10, 2012 at 5:54PM
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Weedmeister... good catch. If there's no power to the pump then it sure won't recirculate. That might be the OP's problem.

Snidely... don't know what you've heard or where you heard it here's the facts about this type of retrofit recirc pump.

The volume of water that is directed to the cold line to keep the hot available can be removed by waiting about 5 seconds after the cold tap is opened.

I've had one of these for over 10 years and have had both the immediate cold and 5 second wait cold water analyzed by a certified lab a few times. BOTH the immediate and 5 second wait cold water met potable water requirements.

As I've stated before on this forum in numerous threads...

1. I'd prefer a conventional recirc system installed at the time of construction.

2. If a conventional recirc system can be added after construction COST EFFECTIVELY with little inconvenience then that would be my choice.

3. Failing #1 and #2 this recirc retrofit design applied in the right circumstance and properly operating does the job, is safe, and cost effective.

    Bookmark   December 10, 2012 at 6:14PM
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I wouldn't want any part of having potentially non-potable water in my cold line, but we can each be happy with what we have.

    Bookmark   December 10, 2012 at 7:42PM
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All water is potentially non-potable... that's what labs are for. When the lab says POTABLE superstition and unsubstantiated opinion hold little water... couldn't resist.

I'll leave you to what you've heard and I'll believe the lab... and we're both happy, but I don't wait two minutes for hot water and I like that a lot. Retrofit recirc has saved me lots of money over the last decade and all that water that would have gone to drain for two minutes every time I want hot water at the faucet hasn't been wasted.

    Bookmark   December 10, 2012 at 8:10PM
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I have absolutely no doubt that the pump will function much better once an electrical supply has been established..LOL

Snidley,,in regards to your statement about drinking water that has passed through a water heater... That is an old wives tale & urban legend that was perpetrated by ppl who have absolutely no knowledge of the plumbing industry. While all the other codes are building codes intended to assure the general safety of the construction within the immediate structure, the plumbing code is not a building code per se.....It is a Health Code and its entire intended purpose is to insure thesafety & integrity of the potable water supply system. You may rest assured that there have been many lengthy studies concerning the presence of bacteria in a water heater, and in each study it was determined that no hazard exists.

Now taking that to the next level, if the system is plumbed with copper the likelyhood of bacteria is even less because as copper ages it forms dark green to black layer on the inside of the pipe, which is copper sulphate, and copper sulphate is one of the best anti-baterial agents known to man, so even if that bacteria did exist, it would soon be destroyed by the copper-sulphate.

Now, while these lang recirc pumps are primarily intended for retrofit, with a minor modification to the installation they in fact have a slight advantage over conventional method of installing the pump at the water heater location.

When the recirc pumps are installed at the water heater location they are either controlled by a timer or they may have an aquastat attached to the return line and by measuring the temp of the water on the return line at the water heater location, they theoretically determine that more hot water is needed at the load end.

A much better system is to install the pump at the water heater location, then install an aquastat at the load end to control the pump, but that means we then have to run a control cable from the load end to the pump.

A simple method is to install a recirc pump as illustrated above, that has the thermostat built in at the load end, but instead of attaching the 3/8" discharge line to the cold water pipe, a 3/8" copper return line can be run back to the water heater, and you end up with the best of both scenarios.

Now here is another advantage of a recirc system that I have never seen discussed in the forums. When a house is built over a crawl space in a cold climate there is a high risk of the water lines freezing in the crawl space. I like to run the hot and cold water lines with about a 1/2" spacing between the lines and also run the 3/8" return line, then I enclose all three lines in a 2" foam insulation. In this manner both the hot water and the return line will provide enough residual heat inside the foam to prevent the cold water line from freezing.

    Bookmark   December 11, 2012 at 12:49AM
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The Laing Autocirc has a temp sensor built in to turn on the pump when the hot water temp drops below a set degree but I don't recall off hand what temp that is. With that feature I believe the best results are mounting the pump at the farthest sink so the sensor in the pump can monitor the temp of the hot water at the far sink location.

Watts has a similar retrofit arrangement where the valve gets installed at the farthest sink and the pump gets installed at the WH but I don't believe the pump has a temp controlled turn on but rather runs all the time or there's a clock (appliance type timer) built in to the pump.

Pup, On the question of potable versus non-potable water wouldn't the hot water have to be potable or it would cross-contaminate the cold water everywhere they mixed?

    Bookmark   December 11, 2012 at 1:26AM
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All water in the water supply pipes within your house is potable water.

In fact, if you were to check the Civil Defense & FEMA emergency guidelines in the event that your water supply is cut off, either from loss of electric to operate a home wellpump or a broken municipal water main, the water stored in the water heater is regarded as a source of potable emergency drinking water.

    Bookmark   December 11, 2012 at 2:10AM
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Thanks for the clarification pup... that's what I'd always heard.

    Bookmark   December 11, 2012 at 10:14AM
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The circ pump is hooked up per instructions, I can hear it running and yes, it has electricity directly behind it into a closet, it cannot be seen under the sink.

I did think of one more thing, not sure if it would effect it or not. The cold water line in the crawl space under the MB has been tapped and is supplying water to my out building. This is approximately 200 feet away. The outbuilding has its own water heater. There is a small apartment built there my son lives in.
Would the pump be trying to supply the out building with hot water as well? This was the closest place to get water to the out building. There is a 1' line tied in there. The house is on a 3/4 inch line.
If this does cause issues, then a hot water heater may be the best answer?
I should mention I have the water heaters available and paid pennies on the dollar for them. I bought 2 50 gallon gas water heaters for $100 each scratch and dent with 12 year warranties at a local store. I also bought a 40 gallon electric, never installed, for $30 at a local store going out of business. So the cost of the water heaters is negligible.
I just want to have hot water sooner after it is turned on.
I can also tell you my electric bill is outrageous. In the winter it can be over $280 and in the summer in the $180's. I have talked to neighbors and theirs is under $100. I realize I have to residences but wow. I did install 22 solar panels and I have seen a drop of approximately $80 to $100 a month on my electric with the panels. These too were a good deal with a State grant and tax right off. If installing a second water heater gets me hot water sooner and if the pump is trying to get the hot water to the out building, would it now make more sense????

Thanks again.

    Bookmark   December 11, 2012 at 10:15AM
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The circ pump has electricity. I hear it running. It is hooked up correctly per instructions.

I did think of another issue. I have my shop, (out building), is tied into the cold water in the crawl space, just under the MB sink. The shop has a small apartment in it and it has its own water heater. The water comes from the closest place it could from the house.

Would this be an issue? The circ pump trying to circulate water all the way to the shop. It is 200 feet away and buried 6 feet in the ground.

If the circ pump is trying to include the shop, I would think a hot water heater and removal of pump would be of benefit. I already have the water heater, picked it up at a local retailer liquidating everything and they had a brand new water heater never installed for $30.

    Bookmark   December 11, 2012 at 11:23AM
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We can quickly rule out the line to the shop because the lain recirc pumps do not run full time.

Inside the recirc pump they have a thermostat that senses the temperature of the hot water line. When the temp in the hot water line drops to 85degF the pump starts and it pumps hot water forward from the water heater to the pump until the hot water temp at the pump reaches 95degF and the pump turns off. The actual volume of water pumped is determined by the size of the hot water line but to give you an example,

a 1/2" line contains 1gal for every 98' of pipe
a 3/4' line contains 1 gal for every 43.4' of pipe
a 1" line contains 1 gal for every 24.52' of pipe

You stated your line is 90' but I doubt if that is exactly correct. If its 90' from the water heater to the pump you have to also consider how long the risers and drops may be, so the line is probably on the order of 100 to 110' actual developed length of pipe, but even with that,and assuminga worst case scenario with a 1" line, the actual amount of water that is pumped per cycle will be under 4.5gal.

Now that we have confired the pump has power, let us begin the trouble shooting phase.

1.Double check to make sure the lines are connected corretly. It appears the lines from the top of the pump up to the fixture are correct, but we cannot see the lines from the sides of the pump to the angle stops. Make sure the line on the right side of the pump is connected to the Cold water angle stop.

2. Check those lines very carefully to make sure they are not making a short radius curve where the neoprene line inside the steel braid could be kinked.(Personally, I would never use those steel braid lines unless the customer absolutely insists. They are the least reliable of all the alternatives. I prefer to use copper tubing).

3. There is PTFE tape (Teflon tape) visible on all those connections. Those are compression fittings and PTFE tape or pipe dope should never be used on compression fittings. It is possible that a small piece of the teflon tape slipped loose while tightening and it is interfering with flow.

4. For the moment, switch the pump from the "OFF" position to the "Auto" position, do not set it on the "Timer" position untill we can confirm it is pumping correctly.

    Bookmark   December 11, 2012 at 12:30PM
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Just -
You've had your hot water tested several times? Why? Didn't the cost of doing that exceed your $$$ savings from not running water down the drain to wait for hot?

I don't need to test our hot water, we don't ingest it. As a test, I let some cool and tasted it - it had an off taste. To each his own I say. As before, we can both be happy with different answers.

Lazy, I respect your knowledge as (you've said) you're a retired plumber. Dumping hot water into cold isn't a first choice approach, I think that's agreed, we can leave it at that.

    Bookmark   December 11, 2012 at 12:45PM
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I rounded up to 90' in consideration of risers and such. Until recently, last month or so, I had always had pump on Auto. Just turned it to Timer recently to see if it would save me some money. I believe it has, but with addition of solar panels during this time I am not 100% sure.

The Teflon tape is 2 threads down on all threads, I did this to make sure it did not interfere. I did not know I did not need the tape. The connections are correct.

As I stated with the pump turned off it will be 4 or 5 minutes for hot water to hit the sink or tub. With it turned on it is 1 to 2 minutes, so it makes a huge difference, just not as quick as I would like.

Maybe this is the best I can expect from the set up?

    Bookmark   December 11, 2012 at 12:50PM
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The long and short of it is that I have a buddy who used to work at the state lab so water tests didn't cost me anything. The reason I had my water tested was that someone, who apparently HEARD what you did, made the same statement you did with no facts to back it up so I had the water tested.

After 10+ years my water usage has dropped measurably since the pump was installed so that water running to drain while waiting for hot water adds UP and has saved me money and my electric bill never has shown a blip since the pump was installed... the water tests safe and potable so IMO a win, win.

I have been aware for a long time that hot water in a home on a municipal water system IS potable but asked the pup to weigh in. I've also been aware for a long time that hot water in a home on a municipal water system IS considered an acceptable emergency water supply.

Now if you're really concerned about "potentially non-potable" consider this... EVERYONE living on a well lives EVERYDAY with "potentially non-potable water" unless they are CONSTANTLY monitoring their water conditions EVEN IF they have installed the appropriate water treatment hardware to correctly treat their water.

And another thought for you... those people who install whole house carbon filters to remove the anti-bacterials added by the municipal water authority are at the same risk of "potentially non-potable water" from bacterial colonization.

Just cause people do it or think it or say it doesn't make anything right or correct... especially when it can be proven right or correct or wrong or dangerous.

    Bookmark   December 11, 2012 at 3:21PM
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I have about the same layout at my house as yours... WH on west end and kitchen sink on east end easily 75-80 feet away, maybe more and my pump works perfect and has for a long time.

Either something is wrong in your installation or something is wrong in your pump. It is that simple.

    Bookmark   December 11, 2012 at 3:23PM
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Is that 90' of pipe insulated in any way?

    Bookmark   December 11, 2012 at 4:58PM
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Nope, just cooper in sheet rock walls with stucco outside @ 7000 ft above sea level. It was 8 degrees yesterday morning and I timed the hot water arrival at the kitchen sink @ 7 seconds.

Don't overlook the obvious things... if the valve in the brass top on the pump isn't working correctly the water won't circulate regardless of the pump running.

Are you sure the pump AC is not switched power?



    Bookmark   December 11, 2012 at 6:08PM
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Have you removed the pump and taken off the brass top to see if hard water deposits have blocked the valve from opening?

    Bookmark   December 11, 2012 at 6:26PM
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Your aim is good, Just. I'd never live in a house with a well. And if I were house hunting. the presence of water filtering equipment in a home would also be a turn-off for me. I'm too much of an urbanite, I don't want to run my own amateur water company. I'm happy to pay someone else to supply and monitor the quality of my water so that I don't have to think about it.

    Bookmark   December 11, 2012 at 8:50PM
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When trouble shooting a problem you do not begin by taking anything apart..that just introduces more problems.

The first step of trouble shooting was to confirm that the pump had power, all the lines were connected properly and there were no kinks in the line that could block the flow.

The next step is to perform an operational test of the pump to determine if the problem is in the pump or the associated piping.

To perform an operational test of the pump make sure that no hot water has been run in the line for 3 to 4 hours so that the line will be cooled well below the pump start temp.

1. Turn the pump off and turn both the angle stop valves at the wall off.

2. Disconnect the discharge line from the pump where it is connected to the cold water angle stop valve.

3. Hold the discharge line in a 5gal bucket and turn the pump on to the "Auto" position. The pump should turn on and begin pumping water immediately, and it should continue pumping until the water in the bucket is 95degF. (About 2 to 3.5gal).

4. If it pumped water into the bucket we have proved that the pumps internal valve opened and the pump is functioning correctly, so there is no reason to take the pump apart.

5. If it doesn't pump water then we have proved there is a defect in the pump. Check the installation manual and they give the procedure for dissasembling the pump and how to check the pump impellor to insure it is properly seated on the motor shaft, and how to check the internal valve gate to insure it moves correctly. (you could try turning the switch to the auto position while you have the pump open to see if the impellor is turning correctly.) Also examine the top cover to see if the impellor has been miss positioned and rubbing on the inside of the cover.

6. If the pump is turning correctly but it still does not bring hot water to the fixture the problem is most likely a defective thermostat. Contact the manufacturer to see if it can be field tested or where you can get it repaired.

    Bookmark   December 11, 2012 at 11:18PM
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