[1acre]

my 1990 house was built with 2 water heaters which each feed a zone. Since we have recirculating loops on each zone, I refer to them as "loops," of which we have 2. In other words, they are plumbed in parallel. When we bought the house, one hot water heater had kicked the bucket, and that heater was removed from the system. The 2.5 yrs we've lived in the house, we've never run out of hot water off the single 50 gal heater, but it was re-plumbed to run at max and then a mixing valve cooled it off a bit before it tee'd off into each zone.

When my wife called my yesterday to let me know the last water heater - from 1993! - had given up the ghost, I decided to replace both. I got them both plumbed up and going how they were originally installed, in parallel. I know in other homes that we've owned which were newer, they installed the heaters in series, one fed into the other. Obviously, the benefit of in series is the combined capacity is available to any where in home, versus it being dependent on where you are using water. But, there is a low probability we would run a single heater (50 gal) out of water is there any other reason to hook this up in series? OR should I just let it ride as is? Thanks!

 

[ddawg16]

If it was me, I'd plumb it so it could operate either way.

Then figure out which method gives you better performance

 

[rjniles]

I would plumb the in series. You could keep the first 1 turned off and use it as a tempering tank. Turn it on if you expect high demand.

OTOH, if you are not running out of water with a single tank, why install 2?

 

[listo]

If it's in parallel I'd be concerned that one is getting used more than the other one. If water flows to the system easier or flows into it easier I'd think it would be used more. Same is true for series I suppose the second one wouldn't have to work as hard as it would always be getting pre heated water.

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[1acre]

I don't know about plumbing it for either direction...seems like a lot of work, and they don't give brass ball valves away.

I think installing 2 is better overall. 1st, the system was designed that way. and 2nd, to meet the demands we had to work the other water heater at full capacity and then mix in some cold water. I'm also certain with 3 young girls (4, 2 and 1 week), hot water needs will increase with time.

It amazes me how well the house was built for 1990. The "zones" are pretty well thought out with the master and laundry on one zone and everything else on the other. I know this because in 1990 (again, amazing) they installed recirc loops and since they pulled off the bottom of the tanks, only one loop was getting instant hot water.

So, I'm not really hearing anything that is game changing....as I stated in the OP, you have an obvious bigger capacity for the entire house. but, input cold water temp is a given and we decide where we want the output temp, so we'll use the same BTU's regardless if we have 1 tank, 2 tanks in series and 2 tanks in parallel. So, there doesn't seem to be any other benefit outside if you want tanks dedicated to a zone or if you want everything to pull from a larger overall capacity, correct? Interested in any other insights....

 

[Ghostmaker]

Good output is a parallel install. A series install makes one tank a holder of water and the other tank works it's ass off heating water.

The best install for 2 tanks and best gallons out is a first one in last one out install that is a self balancing system that allows both tanks to work seamlessly. Notice the cold water feeds the right tank first the left tank last. The Hot water takes water from the left tank first the right tank last. This is a self balancing system. No need to cut pipes to identical lengths. By the way idiot that made picture labeled it wrong.

Each tank should have a ball valve on the cold to each tank And you need an hot water expansion control device mounted on the tanks.