Schematic of a sacrificial anode on a hot water tank (C) Carson Dunlop AssociatesHot Water Heater Piping Connections & Installation
Piping connections for individual vs. cascaded, ganged, series, or parallel water heater hook-ups

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Water heater piping installation & connections:

Here we describe the plumbing connections and piping options for hot water system hook-ups. We explain the piping for a basic water heater installation compared with options for connecting hot water heaters in parallel, in series, or ganged.

Included ar typical time estimates to install a water heater. Plumbing war story: geyser wars: what can go wrong when installing a part on a water cylinder (water heater). We describe a water heater relief valve repair catastrophe when just touching parts leads to a flooded basement.

Page top sketch provided courtesy of Toronto Home Inspection & Education Firm Carson Dunlop Associates.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Water Heater Installation Hookup: Piping Arrangements: single, serial, parallel installations

Water Heater Details (C) Carson Dunlop Associates

Reader Question: in a parallel water heater hookup do both heaters work at once?

My boyfriend is a long time plumber in a small town here in Northern Calif. He wanted me to look up Parallel plumbing on two water heaters for opening a new bar.

I found two sites with the same hookup Cold water to Cold Water and Hot to Hot on cold water. He took the diagram and all the wholesalers in The Chico calif. were perplexed as to why this was shown this way.

Is this a mistake? Or is there an advantage to taking water from bottom of tank. Does this work both at same time or just one at a time.

I found this to be a challenge to see if this was something very ingenious and would like to make sure and understand and share that maybe you are getting more hot water this way or it's a mistake is labeling. Note: see how the cold and hot are hooked up. Thanks for your time in this matter, my boyfriend hooked up the units as always but, my question wants to see if this is more efficient in a bar setting needing more hot water. - C.B. 8/5/2013

Illustration provided Courtesy Carson Dunlop Associates, used with permission

Reply: Piping Connections for Individual & Ganged Water Heater

I'm not sure I have a clear picture of the question but it seems to me that

1. For all conventional vertical reservoir-type tank-type water heaters, we always take hot water from water that is near the top of the tank interior ( hot water rises to the top of the tank interior regardless of how the water is being heated; cold water flowing into the tank to be then heated is delivered to the tank bottom) when delivering hot water to the building

2. There are very different reasons for hooking up multiple water heaters in series versus in parallel as I outline just below

Hooking Up Water Heaters in Series - cascaded water heaters to handle varying demand

In series hookups the hot water out of heater 1 is taken into the cold inlet of heater 2 and the hot water outlet of heater #2 then feeds the building.

This approach is often used for both heating and hot water heating in large buildings and is sometimes called a cascade approach; with proper heater control settings it allows very economical heater operation - we just run one smaller heater when demand is low, but we can run two or more heaters when demand is greater;

In a cascade arrangement the heaters downstream from the first one act as boosters and turn on only as needed.

A variation of the cascade approach is to install a simple water stoarge tank indoors ahead of the heater; water in the storage tank absorbs heat from the ambient indoor environment before feeding the water heater - reducing the heater's workload.

Hooking Up Water Heaters in Parallel - Case 1 parallel water heaters provide individual building area hot water OR Case 2 parallel water heater hookups provide high constant hot water output volume to a single user

Parallel water heater hookups (Which I think you are describing) basically are feeding cold water in parallel to multiple water heaters (i.e. simultaneously) and the outpout from each of the heaters (the hot out) feeds either different building areas, apartments, or users (case Parallel 1) , or feeds a manifold that then joins the output from all of the heaters to feed a single hot water line feeding a large building (case Parallel 2).

Parallel 1 is what we would expect to see in a small apartment building or multifamily house - essentially each tenant has their own water heater - common cold water in but individual hot water out is fed to each tenant or apartment or building area. This approach is economical and allows each tenant to be charged for their individual water heater use (if metering is installed).

Parallel 2, which I've heard-of but never seen and which I think has less application, is in my OPINON an inefficient variation on the cascade water heater approach designed to give a high hot water output quantity to a single destination.

Watch out: keep in mind that there is good reason that the incoming cold water must be connected to the "COLD" marked inlet on the water heater, as the manuacturer specifies - a dip tube is delivering cold water to the heater tank bottom. Hooking up a water heater backwards gives bad results.

For your boyfriend's case, hooking up hot water supply for a bar, to decide how to hook up his two water heaters depends on what problem he's solving. if the problem is adequate total hot water quantity when hot water demands vary significantly over time then he'd want to use the cascade approach - hook up the heaters in series.

If for some reason he has no room for a larger capacity single water heater but needs a large quantity of hot water always available then a parallel hookup (Parallel hookup case 1 above) might be usable.

You didn't say what energy source these heaters use - I'm guessing they are electrical, but the parallel / series hookup question and answer remains the same for all energy sources. At the end of the day I wonder if we were not a bit confused about "parallel" vs "series" hookups of hot watrer sources. If I've misunderstood your situation or question please let me know.

Watch out: your boyfriend, being a plumber, will doubtless convirm another little installation detail that we mention for other readers: the water heater shutoff valve should be only on the cold inlet side of the heater. A shutoff valve on the outgoing hot side of the heater - right at the heater, invites a disaster.

Now what happens if we hook up two or more water heaters in series? The hot out of heater 1 enters the cold inlet to heater 2. But I would not install a shutoff between the two water heaters - doing so creates the same unafe condition. What does the plumber say about shutoff valve locations on a multi-heater installation in series?

Reader Question: how to assure equal hot water flow from multiple water cylinders (geysers, water heaters)

Multiple water heaters in series (C) Carson Dunlop Associates

[Click to enlarge any image]

As Carson Dunlop Associates' illustration (left) shows, one way to improve hot quantity in a building is by hooking up more than one water heater, in parallel or in series.

On a “two hot water cylinders” install, how do you ensure equal flow from each cylinder?

Ref your diagram third down this page HOT WATER QUANTITY IMPROVEMENT - D.R. 2016/01/02 U.K. reader

Reply: easy & hard solutions for balancing hot water supply suggest piping water heaters in series or staged

Good question, D.R. A simple approach is to install an automatic, adjustable flow balancing valve on the heater outlets, but Watch Out: never install a valve that can close off all hot water outlet or you may be asking for an exploding water cylinder.

If two water heater cylinders are next to one another the solution is easier as we can make the input supply pipe lengths equal to each of them from a common tee point, and we can join their outlet pipes at a second outlet tee common point again making sure that lengths, elbows, etc. are the same between the two heaters.

But if you do not combine the heaters close to one another and or even then, if the outlet piping lengths, number of bends, altitude, and actual time and flow rate of hot water usage is not identical, the flow will be uneven out of the heaters.

I prefer piping water cylinders in series in a cascade design for more economical hot water production - that avoids the question entirely.

Reader follow-up:

Cracking reply. Thank you. I think my customer is in for some bad news ... His pipes are totally NOT symmetrical and as I thought that is probably his problem with only one of the two identical cylinders supplying a barn conversion! - D.R.


Interesting. Depending on how the water heaters are located and how their use is intended, I'd consider a revision to pipe them in series rather than in parallel. If you're not familiar with that approach see the article on this page beginning at WATER HEATER PIPING

The in-series allows you to use one of the heaters to boost temperature when the hot water in the other has begun to run out - reducing hot water cost while still providing more hot water quantity. There are a couple of approaches depending on how you set the thermostats but bascially the second of the in-series heaters doesn't turn on until cold water enters it from the now-used-up first water cylinder.

In contrast, an in-parallel piping means that if you could balance the flow, you're providing an equally-large reservoir of hot water even if, as demand varies, you didn't need it. That is, both water heaters will always have to run when any hot water is used from the pair of them.


- DF

Water Tank Piping Connections & Number of Pipes Can Identify the Original Use of Storage Tanks

Attic tank range boiler (C) D Friedman C JonesShown at left are two of five water pipe connections found at an antique water storage tank fonund in the attic of a California home. That tank was ultimately identified and described in detail at SOLAR WATER HEATER ANTIQUE.

The following piping arrangements are discussed in more detail at IDENTIFY WATER TANK USE.

Water Heater Piping Time & Cost Estimates

Reader Question: 9/11/14 If a contractor had the tools and parts present, what is your rough estimate of the amount of time needed to replace a hot water heater feeder if there weren't any technical issues involed. Is it a fairly easy job?

Thanks in advance
- A.S. 9/11/2014

Reply: it depends

Mobile home water geyser (water heater or water cyliner) in an inaccessible location (C) Daniel Friedman Steve Vermilye

I'm sorry but that question is a bit tricky to even try to answer.

There are just too many variables in any plumbing installation to give a number for plumbing work when we have not a shred of information about the job.

I'm not even sure what you mean by "hot water feeder" nor what is involved: piping, lengths, number of connections, accessability, time to drain existing plumbing, re-fill, valves, mounts etc.

Just look at the water heater installed in our photo at left: the location along will add considerable time to any work that has to be done on this unit.

You might as well as me how long will it take me to drive to Christchurch.

Christchurch in what country? From where?

Are we already in New Zealand?
Are we on the North or South Island?
Where are we?
Do we have a car? Or do we need to hire one and get it out of the lot?
Is there traffic?
Do I have to stop for petrol?

Typical Residential Water Heater (Cylinder) Installation Times

There are construction guides with standard "job times" that one could consult but those offer time ranges that do not allow for problems that might be encountered. I'll give an example in a moment.

  1. Typical time to remove an old water heater: 45 minutes to an hour
  2. Time to position the new water heater in place: 30 minutes
  3. Time to complete connections to the new water heater and place it in operation: 45 minutes to an hour.

I make that 2 to 2 1/2 hours if nothing goes wrong. Just below is an example of what can go wrong.

Water Heater Relief Valve Repair Catastrophe

What Could Go Wrong When Tring to Fix a Part on a Water Heater? Why might a plumbing repair job cost more than the original estimate?

In explaining why plumbing job time & cost estimates are just that: estimates, let's use a real-world example of a simple plumbing task: the installation of a temperature & pressure relief valve (safety valve or TP valve) on an older water heater that is itself already in place.

At a home inspection I noticed that a water heater (cylinder) had no pressure/temperature relief valve installed: instead there was a pipe plug screwed into the opening where the TP valve belonged.

Watch out: I informed both the home buyer and the homeowner that this was a dangerous situation as an un-protected water heater, if overheated, can explode, causing a BLEVE explosion that can cause serious damage, injury, even death. For details

I explained that the part itself (a water heater safety valve) was not expensive (less than $50. NZ) and that IF nothing went wrong the installation would be quick: simply unscrew the pipe plug, screw in the TP valve, install a discharge tube, and go. Probably less than an hour of time for the plumber.

The home buyer understood and was not panicked.

The home owner, an elderly woman, began to cry.

"You could fix it!" she wailed. "Pleeeeeease fix it!"

"I could fix it," I answered," but it would be unethical for me to both point out work needed during a home inspection and then offer to perform the work. There is an innate conflict of interest in such operations."

"But I'm a lonely frail widow, living waaaay out here in the country, allll alone, I'll never get a plumber to come out here" she continued.

This debate whined on for a time. The home buyer looked at me with a funny glint in his eye, then he suggested that it would be fine with him if I fixed the water heater TP valve problem.

"I don't have my plumbing tools, no parts, nor anything I need," I continued. "I'd have to return later with the TP valve, pipe dope, tools, and so on" I explained. "

Starting Plumbing SNAFUS:

Then I made my first mistake (of that day).

"OK, OK, I'll agree to do this repair work but only on a 'pro-bono' basis -that means for no fee. The owner can instead make a contribution to a local charity for what a plumber would have charged for a service call. We'll call it $100. OK?"

OK - everyone agreed

Continuing my demonstration of idiocy I drove 40 minutes back to my shop, tossed my plumbing tools in the truck, stopped off at Davies Hardware (106 Main St., Poughkeepsie, NY) to pick up a new TP valve and some new teflon tape. It was surely the case that these would be all the parts I'd need. I already had an appropriate threaded adapter and section of 3/4" copper piping to use for the discharge tube.

I drove 40 minutes back to the job.

Plumbing job time to define the work, get tools & parts, & get to the job:

At the job site I looked at the water heater again. This was a home built in the 1960's.

Snafu #1: I tried shutting off water to the heater

Not one of the shutoff valves in the building itself worked: not at the water heater nor anywhere else. All were either missing completely or were frozen solid. No worries! We could just shut off the well pump and drain pressure from the system.

Snafu #2: this was a big one. I touched the water heater drain valve

I decided to hook up a garden hose to enable draining pressure off of the building plumbing system and out of the water heater (cylinder) itself, sufficient to lower water level below the TP valve opening on the side of the water cylinder tank. Easy. One just connects a garden hose to the water heater tank drain at the tank bottom, then carries the other end outside or to a suitable drain location.

I made a big mistake. Realizing that all of the other stop valves and shutoffs I'd seen in the building were jammed, I thought I'd just try to open and shut that water cylinder drain a bit to see if it worked.

I just touched the handle. Just touched it, I swear. I never even tried to turn it. I just touched it on one edge.

WHAM! SPEW! the handle blew off of the water heater drain. The valve top and valve stem shot into the air and whacked into the basement ceiling, and water geyser ed into the air in a hot fountain.

The owner had dozens of cardboard boxes of stuff stored on the basement floor. This was going to be a catastrophe.

No worries, I could just shut off the well pump so that we'd only drain 40 gallons of water onto the basement floor and onto the boxes of stuff stored there.

SNAFU #3: I tried to turn off power to the well pump

First off the well and pump and pressure tank were not in nor near the home but were about 100 yards up in the woods in a well pit
See WELL PITS if you don't know what these holes are.

I ran 100 yards up to the well pit, kicked away snow, banged on the cover to dislodge it from being frozen in place.

Adrenalin gave me strength to toss aside the huge, heavy well pit cover. And there was the well pit: with three feet of water covering most of the equipment and a fuse box mounted on the wall to power the well pump.

Only an idiot would jump into three feet of water and try flipping an electrical fuse box switch. Well I had already shown who was an idiot but plumbing job time was one thing, life another.

I ran 100 yards back to the house to grab a broom.

I ran 100 yards back to the well pit and used the broom handle to push down the fuse switch.

Happily SNAFU 3a did not occur: the fuse switch did indeed shut down the pump without falling into the water.

By now I had run 300 yards, risked electrocution, got the well pump OFF, AND there was 2" of water all over the basement floor.

Other methods for shutting off building water supply in an emergency are

Plumbing job time to get the water shut off & drain pressure off of the water heater:

SNAFU #3: Remove the pipe plug screwed in where the TP valve belongs

This snafu was predictable: the pipe plug and tapping were rusted solid. At this point any sane plumber would have insisted on replacing the whole water heater. Instead I grabbed a bigger wrench. Stop laughing!

With brains and brawn I got the pipe plug out of the tapping. But the threads into which the new TP valve would have to screw were rusted beyond re-sealing with the new relief valve. Again, at this new point any sane plumber would have insisted on replacing the whole water heater.

A sort of insanity set in. A battle, no a war, between me and the damned heater. I was losing.

Plumbing time to get the new TP valve screwed in and sealed in the water heater

With the new parts on the water heater it was time to turn water pressure back on, refill the heater, turn it on, and check for leaks.

Water geyser TP valve, new (C) Daniel Friedman

Plumbing time to return the water cylinder (water heater) to service

Water heater drain valve (C) Daniel Friedmman

Plumbing time to help owner mop up basement flood & move cardboard boxes

I know some fellows would have been in their truck long before all of this, but really? Leave a soggy sobbing widow sopping up a basement flood?

Drive time back from the job is usually not billed by the plumber so we'll eschew that final 40 minute trip back to Poughkeepsie.

Total time to install a TP valve on a nasty corroded old electric water heater: 6.7 hours.

What really ticked me off: the homeowner never made the requested contribution of $100. to the Poughkeepsie shelter.


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