one hot water tank feeding another

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    • #274606
      James Lowery

      Good Evening, I posted here before and received very favorable responses, but can anyone explain more clearly about the nature of hot water, pressure, temperature ect? I have been heating domestic water with a thermosyphon technique for a couple years now using the old side arm water heating water front mounted in the firebox of my cookstove. I bought a stainless steel water jacket from a company on the net 2 years ago which, by its manufacture alone is different than the old cast iron water jackets of the past. I went with this box which is about 2″ thick by 14″long as an aid in hot water heating knowing that if I went with another approach of 3/4 or I” quick return pipe, that with the constant use of our stove and the way heat contacts around a pipe more efficiently -than I would be blowing off the press/temp relief valve alot. I had qualified licensed plumbers help me hook this system up and I had the temp/relief valve changed to a longer probe when I asked them to come back because I wasn’t satisfied about the first valve they installed since I didn’t feel that it was close enough to be submerged in the top 6 inches of the copper hot water tank that stands next to the stove. We have 3/4″ copper pipe coming from the copper water tank on the stand and 3/4″ coming back into the copper tank after it is heated in the stainless steel water jacket in the firebox. There is a 3/4″ pipe with a temp/pressure relief valve installed and directed close to the floor in the cellar-but not too close- out of anyones proximity. There is a 1/2″ hot water pipe to fixtures that comes out of the copper hot water tank when you turn water on to fixtures. What I had the plumbers do was to feed that 1/2″ hot water pipe to fixtures into the cold supply of an electric hot water tank that stands in the cellar below the kitchen directly under the copper hot water tank that stands next to the stove upstairs. I am having the plumbers come back and check visually and replace the press/temp relief valve this year since we are going on our third year with this system.
      I have tripped the valve off manually on occaision..We leave the electric water heater in the basement on so as we have alot of hot water and as our stove goes about 24 hrs a day in fall and winter-there is always at least warm water going into the electric water heater down cellar and in the summer the copper hot water tank must warm up the water from our cold water well just by room temp before it is fed into the electric heater even when the stove is not in use, I would assume.The electric water heater has a press/temp reliefe valve too that will be replaced this year. I wrote in earlier this year and had wanted to take some further precautions just to be safe and got a reply from your forum that described putting an expansion tank somewhere on that 1/2″ hot to fixture pipe that is fed into the electric water heater in the cellar.We have about 40 ibs pressure that the pump delivers from the well ino a pressure tank in the cellar. My question is: If the press/temp relief valve ever failed on the top of the copper hot water tank in the kitchen would the extra pressurized hot water travel into the electric water tank in the cellar down the 1/2″ hot to fixtures pipe that is feeding the electric tank or would it be fighting the existing pressure that is already held in that pipe that connects the two hot water tanks?? I ask this because I am in the process of having the plumbers come back and install an expansion tank on that 1/2″ hot to fixtures pipe that feeds the cellar water heater but I am unsure of how that would work and am wondering if the water tank in the cellar would act as a place for expansion already and whether it would act as an extra safety feature by its employment of its own press/temp relief valve that exists there; if the pressure or temp ever got as exceeding to make use of an expansion tank employed on that 1/2′ pipe wouldn’t it have to be moving water towards that cellar tank to do so and if it was moving hot water towards that cellar tank in the first place,wouldn’t that in itself be acting as some kind of relief?????
      Thanks again-You guys are good…

    • #290028

      According to Pascal, the water pressure is equal at all points throughout your system (except for the difference in pressure due to gravity which is less than 5 pounds difference from cellar to upstairs tank.) It doesn’t matter in this case which direction the water may travel.

      As you mentioned you have a well expansion tank; as long as you haven’t placed closed valves between your downstairs well tank and a heating device, you won’t need an additional expansion tank; the existing tank will take up heated water expansion.

      The extended relief valve sensor in your upstairs copper tank is a good precaution. Your relief valves won’t fail when letting water out of an overheated system; they would fail if they did not let the water out when the water turns to steam. The most dangerous part of your system is the somewhat uncontrolled solid fuel stove heater. The stainless tank in the stove could overheat and turn the water to steam causing excessive pressures in the system. Hopefully your temperature and pressure relief valve will do the job of letting off steam during an overheat.

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