Proper setup for two 50 gallon gas hot water heaters in SERIES (with recirculating pump)

[Aaron FIsher]

I realize two major mistakes of my last post on this topic:

- How would you set up two 50 gallon hot water heaters in series?

My mistakes were that I confused everyone by mixing series and parallel (they're clearly hooked up in series); and I didn't mention the particulars.

The particulars (AFAIK) are:

- Well pumps cold water out of the ground

- It goes to 10,000 gallon storage tanks

- It then goes to a pressure pump & 40-gallon (approx) blue tank

- It then goes to the FIRST propane 50 gallon hot water heater at about

135 degrees

- The output of that first hot water heater goes to the input of the second (exact same duplicate unit) hot water heater set to the same temperature

- The output of that second hot water heater goes to the house but there is a small grinder-sized hot water recirculating pump in the mix on the final output

From reading this web site:

I find that serial connections:

- Often use non-identical hot water heaters (mine are identical)

- The second heater does almost no work

- All the work is done by the first heater

They don't say "WHY" you'd want this (if both tanks are identical).

They did say that it happens when a house is expanded and this house WAS expanded (they added two bathrooms and a maid's kitchen).

But, it seems to me it SHOULD have been done in parallel (to have more water). Weird, but the web site gives no advantages to serial connections!

They say the parallel connection delivers more hot water than the serial connection. So, I'm REALLY confused now why anyone would design a system with two series hot water heaters that are identical.

[jw]

I'd re-pipe them so one heater serves half the house, the other serves the other half. Especially those with bathtubs (which use the most hot water). If the plumbing change is too much work, at least parallel them. Actually with the proper valves, you could make them for both series and parallel, depending on which valves are open and which are closed.

You have a 10,000 gallon storage tank WHERE??????? I dont get that part....

My whole farm has a 70 gallon (blue) tank. I think the biggest tank I have ever seen sold for residential and farm use is 300 gallon.

Are you talking about a city or town water tower? If so, why do you need a separate pump? I dont understand this....

[RBM]

[teabird]

The series configuration will allow you to increase the capacity without all the repiping required to add another heater in parallel. They simply cut and splice the 2nd heater in the (usually) utility room. To add a 2nd heater in parallel would require additional piping runs to serve the house (usually the new addition) and it's much simpler and cheaper to just add in series.

This could present a flow problem if the extra fixtures are too much for the size of the line. In that case, parallel would be required to allow for adequate flow. For example, the original heater may be on

1/2 inch line. When it's time to add the additional fixtures, they should increase the pipe size up to a convenient branch point.

[teabird]

I just looked at the site you linked and learned something new. A parallel configuration that they describe is the most balanced way to heat your water. In the example they show, they still need to increase the pipe size of the hot water outlet in order to handle the increased flow demand. The benefit to the parallel config is that both heaters will equally be heating water when hot water has been drawn out. This is an advantage when large volumes are used.

The advantage of a series config. are that you can get away with having a lower powered heater as 2nd in line, as that one doesn't have to do much heating (it receives the hot water from the first heater). My setup is with 2 identically powered heaters and I always knew the second heater wasn't doing as much work. In my situation, the first heater's elements went out first, presumably due to overwork.

[HeyBub]

Clearly for redundancy.

Don't ever want to be without hot water.

[Bob Villa]

The 1st is a "water heater"...the 2nd is a "hot-water heater".

[jamesgangnc]

Two in series is to provide more hot water. If you think you have more hot water than you need, turn the first one down or off. For example if you do not have that many people living in the house at the present.

You can't plumb two hw heaters to different parts of the house without significant replumbing work. You can't just hook them in parallel because the flow would never match and you would get temp fluctuations when one of them ran out and the other didn't.

The recirc pump is to provide instant hw at the fixtures it is connected to. That may or may not be all the fixtures in the house. Sometimes they only put recirc pumps on the master bath or in a bath that is really far away form the hw heater.

What you have is installed correctly. Any poster that says otherwise doesn't know what they are talking about. What is your issue with it? Are you just trying to understand it?

[Tony Miklos]

Plumb in series to save energy. The first tank in series only ever turns on if the second tank falls below a certain *critical* temperature. It then delivers warm water to the second tank instead of cold water, so the second tank has the capability to heat it hotter. This way you normally only have heat loss from the second tank.

[trader4]

Well, that must be me. Because in a friends house that is 5 years old he has two water heaters connected in parallel, exactly like the drawing in the link. And I see nothing wrong with it. You claim the water drawn from the two tanks will not be equal. That's likely true. They won't be EXACTLY equal, but with two identical tanks, it's going to be close. Why would water prefer to go through one versus the other? It won't and the water will mix, with no temp fluctuations. As HeyBub pointed out, it also offers redundancy. If one heater fails, you just turn off the valve and you still have hot water. You could even take it out, replace it, without losing hot water to the house.

The only downside to doing it in parallel is that while you will get significantly more hot water, you won't get as much as you would with them in series. As you draw water, both tanks will start to fill from the bottom with cold water. Keep pulling hot water and eventually both tanks will get to the point where the water is now luke warm. That point might be when they both have delivered about 3/4 of their capacity, for a total hot water delivered of about 1.5 tanks.

On the other hand, if you do them is series, you could draw the entire first tank of water with very little temp change. It's being refilled with equally hot water from the second, until the second one in turn starts to run out. Assuming again that occurs when about

3/4 tank of new cold water has entered, you'd get the full first tank of water, plus 3/4 of a tank from the second, for a total of 1 3/4 tanks of hot water.

So, take your pick. Either way is OK, depending on your criteria.

[trader4]

Without two tanks of water already heated and available on demand, he will not have as much hot water available. And you still have to have the second tank warming up water to some temp, so I don't see the energy savings. If energy savings is the goal along with continuous amounts of hot water, then I'd just go with a tankless, assuming the install is reasonable.

[Aaron FIsher]

Actually it's two 5,000 gallon water storage tanks, in parallel, on the property. Everyone here has multiple 5,000 gallon tanks (it's dry country where it never rains from about May to about December, not a drop).

The building codes kick in differently if you have 5,0001 gallon tanks so everyone here has two or three 5,000 gallon tanks (some have four, but that's overkill for home use). The wells run dry often so it could take a week or more to fill up a dry tank.

Hope that answers the question.

[Aaron FIsher]

This makes sense. When they expanded (added two bathrooms and a nanny suite with a half kitchen), they might have simply added the second water heater in series.

I guess what I'll do is turn the first heater down to half of what the second heater is set to (1/2 of 130 is about 65 degrees).

Does that make sense?

- Set the first water heater to 65 degrees,

- Set the second water heater to double that (130 degrees).

That way, both are doing half the work.

Does that make sense?

[Aaron FIsher]

Hi Teabird, Your setup seems similar to mine. Two equally sized series water heaters (in my case, they're both propane as we have few city utilities out here).

What we can do, I surmise, is simply set the first water heater to do half the work that the second water heater is doing.

The only way we can do that, without plumbing changes (which isn't the point), is to set the temperature to half the work load of the second heater.

As far as I can tell, that's our only option for optimizing the system that we're stuck with (without plumbing changes).

[Aaron FIsher]

Hi James, You seem to understand what you're talking about. You make sense.

The only thing I didn't say (I didn't think it mattered until I read your response above) is that the little black recirculating pump is far away from any bathroom. It's in understory of the house right next to the two hot water heaters in series. Nowhere near any particular bathroom.

There is only one recirculating pump (AFAIK) because I can hear it kick in as it hums with an even tone when it kicks on (a dozen or more times a day).

The recirculating pump 'must' be working because we have hot water at even the furthest fixtures in about ten or fifteen seconds.

[Aaron FIsher]

Hi James, Yes, I'm simply trying to understand WHY they did what they did and WHAT I should do with the temperature settings (which is the only thing I 'can' change).

I 'think' now that they simply added a second heater when they added the two bathrooms and the nanny suite (which is far away from the hot water heaters).

I 'think' I should set the first heater (i.e., 'water heater' as someone deftly said) to half the work load of the second heater (i.e., 'hot water heater' as was deftly said).

Since I read the thread about 140 degrees being optimal, I think I'll set the second (hot water heater) to 140 degrees. Now I need to figure out what the first heater should be set to for half the work.

If the incoming water is, say, 50 degrees, I guess I take 140-50=90 degrees and half of 90 degrees is 45 degrees.

Does it therefore make sense that I'm halving the load by setting:

- The (first) 'water heater' to 95 degrees

- The (second) 'hot water heater' to 140 degrees

[jamesgangnc]

I take it you do not have enough people in the house to be concerned about running out of hot water? If not you may want to consider simply turning the first one off. Otherwise your 90 deg setting is fine.

[trader4]

If you want the absolute max amount of hot water possible, then set them both to the same temp, which is whatever temp you want the water to be coming out of your faucet, eg1 30. If you want slightly less max hot water, but some energy savings, then the water heater the cold water enters could be set at the lowest temp. The idea here is that with a lower temp in the first tank, that water will still be hot enough so that after it enters the second tank, the burner in that tank will have enough output to heat it up to the desired temp, eg 130, while water is being drawn. I would suspect the second arrangement offers slightly less max hot water volume, but some energy savings, as the one tank will be holding water at a somewhat lower temp.

[Aaron FIsher]

The only time we run out is when the teen is in the shower.

And, I suspect, it wouldn't matter how much hot water we had, it would be used up until it's cold.

[teabird]

Isn't there supposed to be a loop of plumbing connected to the recirculating pump? So the pump you describe is in the main line after the water heaters. There should be another line coming in at a 'T'.

A recirculating pump moves water in the hot water line to the fixture (as would happen normally) but then it diverts that water in another line to return it to the heater to be heated again (completing a loop). It's this extra line (sometimes referred to as a 3rd line as there are usually 2 lines already (H and C)) that makes installation of a recirc. pump so expensive.

FWIW, I recently installed a Chili Pepper recirc. pump and love it. No more guilt about letting the water run, or washing with cold water. It's a pretty easy install as it uses the cold water line for the return and he have pex tubing under the sink. It's a little loud, but the noise could be suppressed with better padding.

Chris, I think the transfer of heat would be *quicker* because of a greater delta T in the water heater, but not less.