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Master Plumber
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Discussion Starter · #1 ·
How do you guys plumb 2 heaters? I always run them tandem. I think its best for both heaters to be fed and worked evenly. When run in series, one heater is basically just a storage tank. You also can shut down and remove one heater when run tandem. In series you are sol.
Pros, cons?
 

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How do you guys plumb 2 heaters? I always run them tandem. I think its best for both heaters to be fed and worked evenly. When run in series, one heater is basically just a storage tank. You also can shut down and remove one heater when run tandem. In series you are sol.
Pros, cons?

I prefer parallel ( which I think is what you called tandem). Just gotta keep your piping lengths right.
 

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Reverse return or parallel. Depends on which is easier.

Sent from my iPod touch using PlumbingZone
 

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Master Pipe Layer
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I would think that there would be a little more to balancing the draw on parallel installs than just pipe length. Difference in flow restriction in the heat traps and dip tube will affect the balance won't it. There could also be and issue with sediment build up, which will be higher on a parallel install, due to spliting the flow rate in half. Of course it does depend on the application and why you are useing two heaters and not one. You are not SOL when it comes to removing 1 heater out of a series system if they are plumbed correctly. I install all series heaters with a bypass.
 

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Master Plumber
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Discussion Starter · #9 ·
The bigger houses I've done are usually 2 50 gallon power vent heaters. I think the piping looks flossier in tandem, and if one heater fails, you can shut the ball valves and remove the bad heater while leaving hot water available. I think one heater does all the work when plumbed in series.
 

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Master Pipe Layer
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The bigger houses I've done are usually 2 50 gallon power vent heaters. I think the piping looks flossier in tandem, and if one heater fails, you can shut the ball valves and remove the bad heater while leaving hot water available. I think one heater does all the work when plumbed in series.
One heater doesn't do all the work, but it does do alot more than the other. Because of this the second heater recovers quicker. You can remove one out of a series and leave hot water available if plumbed correctly. The tandem or parallel is a cleaner and easier install though.
 

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How do you guys plumb 2 heaters? I always run them tandem. I think its best for both heaters to be fed and worked evenly. When run in series, one heater is basically just a storage tank. You also can shut down and remove one heater when run tandem. In series you are sol.
Pros, cons?
I don't agree that you're s.o.l. if run in series. You can put in the isolation valves & tee to allow by-pass of either unit in the event of maintenance/replacement of either unit.
 

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Left set to low, right set to high (normal setting). 9600 sq ft home 9 bath. To answer you question though, I think it all depends on size of the heaters, efficiency or recovery rate, gas vs electric, needs of homeowner/builder. So there are a few factors to through in the mix.
 

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Plumb or Die!!
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My experience with this has often started in an apartment mechanical room with the manager saying, " I've run this building for 20 years and we've never had an issue with this hot water heater. The one beside it, however, has been changed 5 times."

Without fail, the original installation was series tanks. The one with the cold water inlet does all the hard work, the other one just simmers quietly to itself.

In my umpteen new school builds and oodles of reno's, I've never seen series tanks on a blueprint.
 

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We all know that undersizing a water heater is bad news. Customer is not happy because they're running out of hot water and when talking gas heaters, the flue condenses. So when the demand is such that two water heaters are needed to eliminate the unhappy customer and a series arrangement is used, the first one experiences the same set of issues an undersized water heater does, IMO.
 

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Left set to low, right set to high (normal setting). 9600 sq ft home 9 bath. To answer you question though, I think it all depends on size of the heaters, efficiency or recovery rate, gas vs electric, needs of homeowner/builder. So there are a few factors to through in the mix.

Wow, 2 flue vent heaters in a new build!! Been a few years since I've seen that. And what is that orange colored piping feeding them? Must be a new plastic...

We typically install in a series. I'm sure that the primary tank will die first. But not sure it would die any sooner than installing just one heater. I'm thinking we're gaining a few more gallons this way. (I'm no engineer, just a plumber) Seems like most of the time we end up with a 50 gallon power vent as primary and 50 gallon electric as the storage tank.

Not a fan of tankless for big houses. People always bi**h about hot water pressure. Most of the people who can a afford a monster house don't care about saving a few $$ on energy. A $300+ gas bill doesn't bother them.
 

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every tool is a hammer
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I have seen parallel installations where one does all the work, and the other is just on standby. I usually pipe in series, because most of my dual installs are really just adding a heater to an existing one, and there isn't room or time to pipe in parallel, so I go series. The first heater is usually set at 135 and the second at 145, by the time the water gets to dish machines, it's 140.
 

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Illinois Licensed Plumber
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Parallel. First in --- last out

Nobody cares that this was sent from my droid using. Plumbing Zone
Here is a diagram of the First in --- Last out parallel piping, its quick its easy and it works all the time.

 
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