Piping 2- 50 gal. water heaters to work in sync

NoeV

I would like to correctly pipe two individual 50 gallon water heaters to work in sync. As opposed to just having one 100 gallon water heater. Is there a correct way or wrong way to do this? I'm using 3/4 copper pipe.

Abracadabra

NoeV said:

I would like to correctly pipe two individual 50 gallon water heaters to work in sync. As opposed to just having one 100 gallon water heater. Is there a correct way or wrong way to do this? I'm using 3/4 copper pipe.

Just make sure all piping between the two heaters is exactly the same size.

icesailor

And EXACTLY the same length of pipe, with the tee EXACTLY in the middle. Don't ever forget that water seeks the path of least resistance.

NoeV

Thanks for the info. The Tee being in exactly in the center is the crucial part. I'm not sure what would happen if I feed the 1st. water heater with cold water then add pipe until I reach the 2nd. With the Tee being closer to the 1st. Water heater.

NoeV

In addition , what plumbing issues would I encounter if I pipe the cold water normally to the 1st. that is; without a tee but then the hot water side feed into the cold water inlet for the 2nd. water heater. So in a sense 1st. water heater feeding the 2nd. water heater (pre-heating) and the hot water side on the 2nd. water heater feeding hot water supply.

Jamie Hall

As Ice says, any unbalance in the piping is going to lead to one water heater doing the work and the other one just sitting there.

In your second scenario -- with one heater serving essentially as a preheater for the second -- the load on the two units will be very different; the second one -- depending on how the temperature controls are set -- may wind up doing almost nothing on lower flows (up to the recovery capacity of the first unit). Not quite convinced that this is a good thing...

In fact, not quite convinced as to why one would want two heaters at all! But you must have a good reason...

NoeV

What if any are the advantages to having just one- 100 gal. water heater system as opposed to a having two- 50 gallon water heaters?

Abracadabra

NoeV said:

What if any are the advantages to having just one- 100 gal. water heater system as opposed to a having two- 50 gallon water heaters?

With 2 -50s
1-Easier to get into tighter spaces, doorways.
2-If one heater goes out, you still have some hot water out of the 1 left.
3-Material cost for the 2 50s will be cheaper since 100s are considered commerical.

Most 100G will have a much better recovery than 2 50s
Labor for the 2 50s will be more. twice as much piping to do.

icesailor

Not if they are electrics. You get twice the recovery with two balanced electrics than with one doubled in size heater. Only one of the two elements work at a time.

Gas is a different animal. But like you said, a 100 gallon is considered commercial and commercial regulations can come into play.

Jamie Hall

Which all leads me to this question: do you really need 100? Because in the ark I care for, there is one 80 -- oil fired -- which is more than adequate, and that is a residential size still. At least in this area...

icesailor

Jamie,

Electrics are the slowest to recover, around 18 GPH with a 4500 watt element. Only one runs at a time. Gas is next but 30's to 50's have a 35,000 to 40,000 BTU burner and we always understood them to recover about 36 GPH. Oil is a different animal altogether. Because of their high recovery rate, they are prone to "stacking" with short draws. Most oil fired water heaters are considered commercial water heaters. 75 gallon gas water heaters are usually considered commercial water heaters. With 75,000 BTU input and up.

For me personally, in the wild Electric heat days, the local power company required 80 gallon electrics to get their rate. But the recovery was the same whether you used a 20 gallon electric or a 120 gallon electric. For my customers that wanted more hot water, I used two 50's, carefully piped to be equal with a recovery rate of 36 gallons per hour. Because each water heater had its own element running.

I worked with a designer who hated cellars. Only crawl spaces. I once did a house with a 12 block crawl space. The house was on a hillside. There was no inside access to the underneath, You had to walk all the way around the house and down a hill. To get to the two 50 gallon electric water heaters. Two smaller water heaters will always outperform a larger single one.

hot_rod

I think it depends on how you use DHW. In the resort areas we piped the tanks in series for rental and vacation homes. If a couple used the home 1 tank was plenty. During holidays when the homes were at full occupancy they could fire both. This would double the recovery and dump load.

During off season the first tank was put in the vacation setting, pilot still on but lowest possible setting. Or booth in vacation mode if the homes were taken out of the rental pool, crank them on when the owners showed up..

Two tanks gives you more options, possibly a lower installed price also.

kevin_58

After April 2015 new federal energy standards take effect and it will be way cheaper to install 2 smaller heaters and if one leaks you can shut it off and still use the other.

NoeV

The two water heaters are for a 6 - unit apartment building in Chicago. Each apartment is a two bedroom. I'm replacing the 20 year old units after one failed. I should have replaced the anode rods on both of them 10 years ago perhaps.

NoeV

The following picture shows the two 20 year old water heaters.

Jamie Hall

all fair enough -- just curious.

icesailor

NoeV said:

The following picture shows the two 20 year old water heaters.

If the two heaters are feeding more than one apartment, and they run out of hot water, if you could check the heaters when they first run out, you would find that one is cold and the other is partially how. Because of the way they are piped.

hot_rod

Reverse return is another common method. Here is an article from Plumbing Engineer mag

RobG

hot rod said:

Reverse return is another common method. Here is an article from Plumbing Engineer mag

I find reverse return is easier than doing the "pyramid" piping arrangement, especially if you have more than two appliances.

hot_rod

agreed, much easier to pipe. ideally you reduce and increase the pipe size as shown for true "self balancing'

icesailor

If you have two heaters and you want to call it a "Pyramid", that works fine as long as it is perfectly spaced. Three or more, and the only way is with a reverse return.

A couple of years ago, someone from Hawaii had a condo with multiple water heaters connected as a reverse return that he had problems with. He never stated if or how he fixed it.

NoeV

In the reverse return layout do you just then cap off the hot outlets in order to use the drain as the new hot supplies?

Larry Weingarten

Hello: I'd be tempted to go to a sizing program, like RightSpec by Bradford White and put in your numbers to see what they say is the right size hot water maker for your situation. From there, assuming you want to use two heaters, it would be nice to know the maximum likely gpm flow. If it is low, (because your tenants don't all go to work at the same time) you might be able to use 3/4" connections on the tanks and series plumbing. Series doesn't get out of balance with the build-up of rust at fittings or other reasons. Using two tanks allows you to bypass one and have some hot water at all times, which I'm sure the residents would like. There are other factors to discuss, like a recirc line, (which affects the dynamics of hot water flow) or even using this opportunity to install low flow fixtures... which could allow you to buy smaller heaters.

Yours, Larry

icesailor

NoeV said:

In the reverse return layout do you just then cap off the hot outlets in order to use the drain as the new hot supplies?

I consider that drawing with the connections at the bottom of the water heater tanks to be foolish.

Use the ones at the top. You will have to cross over and have three parallel pipes at some point if both pipes enter from the right or left.

Entering from the right, the cold" Right tank first cold, second tank (left) cold. First tank, hot, second tank first. If you want to do a reverse return with two tanks. It is easier to pipe two tanks exactly equal.

icesailor

Larry Weingarten said:

Hello: I'd be tempted to go to a sizing program, like RightSpec by Bradford White and put in your numbers to see what they say is the right size hot water maker for your situation. From there, assuming you want to use two heaters, it would be nice to know the maximum likely gpm flow. If it is low, (because your tenants don't all go to work at the same time) you might be able to use 3/4" connections on the tanks and series plumbing. Series doesn't get out of balance with the build-up of rust at fittings or other reasons. Using two tanks allows you to bypass one and have some hot water at all times, which I'm sure the residents would like. There are other factors to discuss, like a recirc line, (which affects the dynamics of hot water flow) or even using this opportunity to install low flow fixtures... which could allow you to buy smaller heaters.

Yours, Larry

Are we talking about tank type water heaters or tankless indirects? They are a different animal.

Hilly

How about addiing a re-circ to multiple water heater installations? Anyone have a diagram for that?

RobG

NoeV said:

In the reverse return layout do you just then cap off the hot outlets in order to use the drain as the new hot supplies?

Just use the standard top ports. It's hard to describe but simple to do. I will try to describe it. Take the letter "F", rotate it 90 degrees so that the two prongs are pointed down (those will be your cold connections) Do the exact opposite for the hot.
The letter "F" flip flopped so they are facing the opposite directions. I don't know if that made any sense but maybe someone can draw it. It's really very simple.

icesailor

If you want to use return circulation, you should return to all the bottoms equally. That the hot water in the tanks will stay in some sort of balance. If you go into just one, all the flow runs through the one radiators and the others may not be used.