Water heaters in series
thrifttrust| Posted inGeneral Questionson
I’m preparing to install solar soon. To connect to the grid I have to demonstrate to the utility that I can use all of the electricity I produce. While I intend to go all electric in the future, presently, we use gas for space and water heating. We purchased a used Chevy Volt to increase our electric needs and I am considering installing a used 30 gal. electric water heater.
My question is: Can I connect the input of the electric water heater to the output of the existing tankless gas unit? Turning on or off the tankless unit would give me control over how much electricity I actually use.
Douglas Higden
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Replies
I'd just use parallel valves to select one or the other (enabling elimination of unnecessary standby losses powered by expensive electricity). But I don't really understand your use case.
I like the idea of series the A or B install adds the risk of bacteria growth in the unused heater.
You may want to add a tempering valve to allow the water heater to operate a higher temp and not risk burns at the faucet.
A good used water heater is a rare find as most will run them until they fail or are very old.
Walta
Douglas,
There is nothing wrong with putting the two heaters in series. This is one way with tankless units to eliminate the cold water slug effect and reduce hot water delay time (normally it is a small 6 gallon tank, but a full size one would work the same).
You just have to set the thermostat on the water tank to a bit bellow your tankless output temperature. If the tankless is running and you are using the hot water, the electric element would rarely if ever turn on. If you are away or not a lot of water is used, the element will turn on to make up for the standby losses of the tank.
To what Akos has mentioned, I've seen some installs where the gas tankless water heater is the primary and goes through a holding tank which I suppose can be electric. Basically you can turn the gas heater on or off for your needs.
I'm installing an HTP crossover which in the install drawings they show this kind of setup. Check out the install specs for the RGH-199 to get an example.
Also, I agree with Walters comments as well, check out matt risingers videos on taking apart used water heaters. Also, be sure in our setup to plan against legionella. essentially want to make sure the water temp is high enough to kill that bacteria.
Thanks for the advice guys.
The HTP looks like an interesting product. 199K BTU is a lot of heat!
I just picked up my Craigslist 30 gal. It had only been used for a month or so when the owner could not use his chimney during a renovation. It looks brand new.
I'm guessing the water cannot be hotter than the setting on the the hottest set unit?
I'm in the process of filling out a request for net metering. The utility requires that I prove that I can use all the power I produce. Later, after I energy retrofit the house, it will be heated by mini-spits, but for now, the car, the resistance water heater and window air conditioning should justify a 10K solar array. I was thinking smaller until the utility's calculator showed that the 10K array, facing due south, at an angle appropriate for my latitude and my estimate of 10% shading showed an annual production of only 9827 KWH. Welcome to Michigan. The great lakes are beautiful but they kick up a lot of clouds.