Hooking up 2 seperate Hot water heater together.

[Clarence Martinn]

If you have a duplex where you live in one part , and the separate apartment is not rented out, how do you hook up the unused Apartment's water heater to the other water heater? Obviously, there would need to be some sort of 3 way valve to shut off the diversion of water from the 2nd tank to the 1st tank; after the apartment is rented. Is this possible to do ?

[Mike Cutler]

Clarence
It's definitely possible to do. Easy, on paper at least. Whether or not it's a code violation is a separate issue.
Basically both water heaters will be put in parallel and you just tee off one to the other making sure that you can isolate,either ,from the other, and the supply.
Do you need to tee off the supply?
Unless these water heaters are right next to each other though, by the time you get done buying valves, pipe, poking holes through walls and studs, it's going to be quite an effort.

[Tom M King]

A check valve would do what you want, or a couple of ball valves. It doesn't have to be anything complicated. We have two water heaters in series. The first one serves the old part of the house. The line T's to serve another water heater because we have a Jacuzzi in the master bath that one alone won't fill, but we don't use it often enough to be worth having a separate system, with a large water heater.

That makes the second one a hot water heater. It works just fine. If utilities are including in the rental price, there might not be any need to even have the check valve.

[Mike Cutler]

Tom
The hot water outlet from the first, is the cold water inlet to the second? Why not just parallel them?
We had two paralleled for awhile. The flow checks stopped them from back flowing through each other. There is only one, bigger propane unit, now. They were right next to each other in the basement.

[Tom M King]

Yes, the inlet on the second one is the line coming from the first one. I doubt that the flow through both, in a parallel system, would allow only all the hot water to get to the Jacuzzi without having some unknown amount of cold water to also get through before being heated. The pipes going to the Jacuzzi are large, so it doesn't take long to fill it. It just seemed too complicated to get the flow right through a parallel system. Being simple minded, I like simple. The connecting pipe between the two heaters is very well insulated, so there is not a lot of heat loss there.

[Bill Dufour]

Why? just shut off the unoccupied unit WH. Are you planning the same thing for the power supply as well?
Bill D

[Kev Williams]

I'm thinking 'in series' like Tom, it would assure water keeps moving equally thru both tanks. And I don't believe in check valves, every one I've ever used leaked in short order...

I'd do it like this, similar to bypassing the water heater in an RV for winterizing...

[Clarence Martinn]

1. Water heaters are in the basement . About 2 or 3 feet apart from each other.

2. Water heater for Downstairs is Electric. Water heater for the other unit is Natural Gas. I got the electric one. It's also smaller , gallon wise. Never seem to have enough water.

3. The electric water heater is really expensive to run. Want to switch over to Natural gas someday. But , while the other unit is not rented out, I figured why not hook both of them up together. When I ever decide to rent the unit out, I would just switch the gas water heater off from flowing to my end of the house.

[Clarence Martinn]

Is that like this ?series water heater.jpg

[Myk Rian]

Pipe the gas heater into your system with valves, and turn the electric off. Just by-pass it.

[Bruce Wrenn]

Which unit pays the gas bill? If it's yours, drop the electric completely, or use it as a storage tank. To use as a storage tank, hook electric in series with gas WH receiving hot water from gas WH. Set thermostats (you most likely have an upper and lower) to 10 degrees colder than gas heater. This way during long storage periods, or heavy usage, water would remain hot. At a later time, you may need to install a larger gas water heater when other unit is rented

[Bill Dufour]

Look into a instant gas water heater to replace the electric one. More efficient then a standby tank. Just know the incoming water temp before buying.
Bil lD

[Perry Hilbert Jr]

Gotta Agree, WHY? If it is just a matter of not getting enough hot water a larger water heater for your side would do the trick. Some codes provide that units that pay their own utilities must have totally separate water heaters. (not in the building code but the rental housing provisions. Old trick here was to make tenant responsible for utilities and then have the landlords hot water on the tenants bill.) If you other unit would ever be rented out, you might need the units separate again. Electric water heaters are not that expensive. I just put in a 60 gallon water heater and the cost was $399 plus $35 for the installation. At the old house we had a "pre heater" system. Cold well water went through the outdoor boiler before going to the water heater in the house. Even in the summer when the outdoor boiler was not fired, it was warm just from sitting in the sun all day and so the well water was warmed at least 15 degrees before going to the water heater.