Proper setup for two 50 gallon gas hot water heaters in SERIES (with recirculating pump)

[jamesgangnc]

I prefer the 3 line solution. When you use the cold water line as a return then you have to run the cold water a while to get it cold. So it just switches the one you run.

[trader4]

Also depending on what else is on that cold water line, you could easily wind up with that stale, tepid hot water coming out of the kitchen faucet. Not exactly what you'd want when drawing water for cooking, making drink mixes, etc. In fact, if you get into a situation like that, you could wind up wasting more water. But, in the right application, the pumps under the sink at the far end offer a solution when retrofit would be expensive.

What really sucks is that I regulalry see new construction with $1mil

4,000 sq ft houses and they don't put in that extra line at build time.

[Tony Miklos]

I don't think your setup is working properly. It would be difficult for it to run out of hot water. How many gallon are the water heaters?

[Willie]

Simply, if you have the two water heaters in parallel, you will need to have both set at the exact same temperature and that would require having two water heaters that are exactly the same. Even with that requirement, you don't know if the two thermostats are measuring the temperature at the exact same point. Why that is important? because in a parallel configuration, each tank provides half the amount of hot water. If one tank is delivering lower temperature water, then it will lower the temperature of the water line.

In a series configuration, one water heater, provides the hot water and the other one, the one receiving the hot water, will turn on when the water gets at a lower temperature. Hence, it is really a "Helper."

In the parallel configuration, both heaters are working to heat up the water at their set temperatures. Hence, you are wearing out both water heaters simultaneously. At very a very near time both will break and you will have a double wammy as you will have to buy two water heaters. In the serial configuration you will have one, the first one that will break first. Given the proper maintenance, the second one will continue to work as normally. The problem I have with the series configuration is that the one I have at my home have two different thermostats. Hence, I don't know what temperature points I am getting out of the entire setup. Hard to say what is the total effect of the final temperature. I would say, set the second one at a higher temperature than the first one. In that case, the first one will not cool down the second one.

That is what I am thinking.

Hope this helps.

[trader_4]

Why would that be? Suppose one is 5 deg hotter than the other, what's going to happen?

and that would require having two water heaters that are exactly the same.

Why would that be? Two different tank water heaters can't be adjusted to the same temperature?

Even with that requirement, you don't know if the two thermostats are measuring the temperature at the exact same point. Why that is important? because in a parallel configuration, each tank provides half the amount of hot water. If one tank is delivering lower temperature water, then it will lower the temperature of the water line.

Unless the second one in series has water constantly heated to the same temperature as the other tank or close to it, it's not going to be of much help when you need it.

That's not true if the second one is full of hot water, which is what is needed to get double the supply of hot water.

Turn the water to one off at a time, measure the water temperature at a faucet.

[Scott Lurndal]

Water expands when it is heated. Perhaps the expansion into the colder tank is not a particularly good idea?

At what precision? And how accurate are the tank heater theromostats?