Question about H20 tanks

ok, ive seen this twice in the past week and i dont understand the purpose. first of all, neither house needed two hot water tanks as they both had only 2 baths?? and btw, i could not determine where the shared line was going as it was concealed in the basement ceiling.

Thanks in advance

I’m sure you would have noticed, but I would guess the reason for two tanks is either for radiant heat or solar assisted hot water generation.

Edit: I can’t tell if the left tank is connected to the gas supply. If not, then it may be being used as supplemental storage for an alternative energy system (e.g. solar, geo-thermal)

I had an older home that had two water heaters and it was three bedrooms, we just wanted to have a separate water heater for our master bathroom since the tub was so big. I have no clue the circumstances in Ohio but I’m sure someone will chime in.

thanks for the replies. heres a little more info for you. one house had a radiant heat system with boiler and the other didnt. both had this exact same setup on the water tanks. neither had any solar heat/recovery system.

radiant heat water wouldnt share with the potable water supply.

It is possible to use the water heater(s) for just that purpose.

The shared line is to back flush the heater. It isn’t done quite the way I’ve seen others but serves the same purpose. I have also seen this done to have hot water throughout the house. Hot rises through the system and then as it cools it moves back down to the heaters. I think it is called a kinetic return. Just run the Hot in a circle.

it didnt appear that these lines were running back to the boiler. BUT, if they were then all the water from the boiler and radiators would be mixing with the potable water??

The shared line is a gravity recirculation loop. It connects to the far end of the hot water line. as the hot water cools off, it becomes more dense (heavier) and falls down the recirculation line to the bottom of the tank to be reheated. This results in a continuous flow of water through the hot water piping at all times so you don’t have to wait for hot water at the faucets

There are various designs to radiant heat systems, and some do share the water with the potable water system. Those that share the water are called open loop radiant heat systems, those that do not are called closed loop radiant heat systems. The same can be said for solar heating systems, open and closed loop.

Also, as someone else said water heaters can be used for the heat source of a radiant heat system if the ‘heater’ does not need extremely hot water. Most radiators need water in the 180F range, but radiant heat floors operate well at 100F. In fact most radiant heat floor companies recommend water heaters for the heat source now because running boilers at such low temperatures seems to cause them to wear out quickly.

For your reading pleasure I suggest:

– bz

My big concern with using the Home water for heat is the posibility of Bacteria growth with the water not being hot enough.

In 2000, the Walkerton disaster had sent a wake-up call about the safety of Canada’s drinking water. While standards for domestic hot water must consider scald prevention, they must also address the broad spectrum of public health and safety issues. To minimize bacteria contamination, water must be stored at 60 C or higher.
For example, temperatures under 50 C may increase the risk of Legionnaires’ disease, a form of pneumonia, due to bacterial growth in the tank. That disease is caused by Legionella bacteria, which live in water. Temperature is a critical factor for Legionella to grow. The risk of colonization in hot water tanks is significant between 40 and 50 C.
Legionella bacteria most often enter the lungs due to aspiration. (Aspiration means choking such that secretions in the mouth bypass the choking reflexes and enter the lung.) Drinking contaminated water is not a major cause of Legionnaire’s disease.
The Centers for Disease Control and Prevention estimates 8,000 to 18,000 Americans contract the disease annually. Five to 30 percent of the cases are fatal. While Canada has no national statistics, Hydro-Québec says about 100 people a year are hospitalized in that province for pneumonia caused by contaminated residential water heaters.


And that is why a properly designed system will use a mixing valve to control the temps in the domestic and radiant heat runs.

Roy -

I agree that if a system is not properly designed then that would be a concern. I had similar concerns when this solutions was first proposed to me, and I spent alot of time researching it before I installed one.

The claim was made earlier that “radiant heat water wouldnt share with the potable water supply”, which would be true in many situations, but not in all situations. I was just trying to educate those who didn’t realize that there are properly designed radiant heat systems which do mix potable water with the heating system.

There are several trade-offs in each design, and this solution is no different. It’s certainly not the ‘best’ solution for all situations, but it is a recognized, valid solution which has it merits and is being installed more frequently. From my experience the system turns out to be very simple to operate and maintain and very efficient, especially when a solar heat source is being used.

If you are interested in a discussion of the benefits of one design over another feel free to contact me.

– bz

Although, this is a very simplified drawing it might give you an idea what I’m talking about.

Hot Water Radiant Water Flow.jpg

yuk! i cant imagine that type of system in the house in question that was built in 1898 with its original radiators.