Water Heater Question - Serial or Parallel?

[HEEP]

SO we have a new house and it has two water heaters due to the amount of bathrooms by code. The question I have, should they be hooked up in a series or parallel? In the series, one is working harder than the other as it is sending hot water into the second heater? I thought It should be parallel, as both should be heating water at the same time.

I thought I would come here to see what others thought.

Thanks,
Bill

 

[marinusdees]

SO we have a new house and it has two water heaters due to the amount of bathrooms by code. The question I have, should they be hooked up in a series or parallel? In the series, one is working harder than the other as it is sending hot water into the second heater? I thought It should be parallel, as both should be heating water at the same time.

I thought I would come here to see what others thought.

Thanks,
Bill

I have two 50 gallon gas water heaters hooked in parallel. The installer, the subcontractor for the gas company, turned out to be a personal friend. Initial install, I said, "Sam, I have four kids, I want a 100 gallon water heater." He said,"No, you want two 50s in parallel." They've lasted 50 years, puked last year. Kids are gone, I replaced with two 50s in parallel. Don't mess with success.

 

[The Cobbler]

I would do in series, more stable temps when nearing the end than 2 in parallel IMO
in parallel if the one has more water taken off than the other you would get cooler water when it nears the end.

 

[jlv03]

What will be the fuel source? Electric? Natural gas? Propane?

 

[Bert_]

I've put them in series the couple times I've done it.

Depending on the piping, if you plumb them in parallel one will run out of hot water before the other. Then you are just mixing cold water with the hot from the other.

People here always get worried about appliances "working harder." Most of the time long run times are better for the equipment and if it's gas, more efficient.

 

[larry4406]

I have only done one new house with twin tanked identical water heaters. They were old school B-vent units (probably 10+ years ago).

Plumber did them in parallel but was meticulous on matching the length of the hot and cold piping and fittings. He said doing that, the units would draw down equally and have equal duty vs a series arrangement. His installation was similar to this crude sketch.

Customer never complained, but who knows.

 

[fitter30]

When heaters are piped in series the first heater catches 80+% of the minerals. Larry 4406 show heaters piped reverse return. First in last out gives you equal flow through both.

 

[rharman]

When we had duals, they were in a hitch loop.

 

[HEEP]

Thanks for the feedback guys. Still a little confused, but it seems that both ways are acceptable. I'll need to see what I can do to make equal length lines as larry4406 shows in the diagram.

 

[jblnut]

I've helped plumb dozens of dairy barn projects and every single water heater or heat recovery unit setup has been plumbed in series. The first water heater is set lower then the next and so on. The theory is that they share the load and all do at least a little work under a high draw.

One of the last ones I was involved with had 4 50gal tanked heaters and two on demand units after them to pick up the slack as needed. There was also a recirculating pump between the tanked heaters to keep them all as balanced as possible.

That wash system needed over 500gal of 140f water every 12hrs and it easily supplied it.

So long story short .... I vote series.