Temp/Relief valve-wood fired hot water

[James Lowery]

Long story-bear with me. For about three years I been heating domestic water in an old fashioned way using an beautiful old cookstove and a water jacket or water front in the firebox.The water tank is copper seamless that stands on a stand and this set up is what was seen, and still is to some degree in alot of homes here in Maine.I guess that this heating is called a thermosyphon.This tank is even less common than some that I have seen around here because the ports that are usually located three quarters up the tank and three quarters down its side along with the couple on top are different here. There is one openeing 1/3 from the bottom and the other 2 are at the top and of course there is a port on the very bottom. When I entertained having this all hooked up I found an old plumber who has a long standing buisness here. He was, as we say in Maine”Tickled to death” to help me with it.It felt really good to connect with this guy because of this commonality that brought nostalgia to him and an appreciation of plumbing to myself. I was thinking more in terms of a 3/4 inch pipe with quick returns or a cast iron jacket in the firebox.3/4 and 1″ is what I have always seen for pipe in these-but he went with 1/2 soldered copper and made a rectangle going around the top of the firebox and he had the cold going in stove from the tank coming out the very bottom of the tank and the hot return from the stove going into the tank in that port that is 1/3 up the tank from bottom. He Said that we use the stove so much that it would be sufficient,incidentially he never came to do the work after we met but sent plumbers over with a diagram he made. The water never got hot enough to even wash dishes with and when I called him he said that after the pipe inside the firebox got blackened that it would make quite a difference-It never made any difference…I bought a stainless water jacket about 16″long by 5 or 6″ high.I came out with 3/4 pipe from the port that is 1/3 up from the bottom
for my cold going in the stove and came out keeping an upward pitch to the top of the tank with the hot return and called the plumbers back to help with the final touches.I didn’t like the cold coming from the very bottom after I found an old plumbing book that said without a filter in there, you could pick up debris and clog something. The way I connected it at top I guessccording to this book,is called a quick connect.Now the plumbers helped me put the temp/pressure relief valve on top but since there were two fittings already on the top(the hot from the stove and the hot to fixtures)this fitting would be the third but also the book suggested that the probe be where the hottest water was ,6 ” in the top and I asked them for a longer probe. They laughed and said that where it was was the hottest part cause its all filled with hot water.After they left I bought an extened probe and felt better.Now I also had them drop the hot to fixtures to an electric water tank in the basement but I wanted valves so if something happened to one tank it could be isolated to work on. Now the hot going to fixtures from upsairs tank goes down into the cold fill pipe of the electric tank in basement.This has brought all kinds of smiles to the older folk who come buy who seem to all have grown up with the one tank upstairs and never have I heard of an explosion story from these people. I have noticed that with really dry wood this year the coals are allowing for more heat and once in a great while the temp/pressure relief valve will go off and there sometimes is water in the cellar.We had one person move out so there is a little less water consumption and once in a while you can hear the tank sigh if the hot water hasn’t been used much all day. I periodically test the relief valve manually but also, reading in the old book were incidents of explosions that I never heard from anyone.The book said most were gas heaters that were left on all night and there were no relief valves or there were and they were shut off-It said too, that enev a leaky faucett was enough to keep the tank regulated. But I got scared as hell so FINALLY MY QUESTION….. Should ,even if I have the temp/pressure relief valve visually inspected this year and replaced- Should I find a way to have another temp/relief valve put somewhewre also to set my mind at ease??? We have saved tons of money on electricity and I keep the electric one on so there’s quick recovery for baths ect,we have a drilled well and even when the stove is not used in summer ,the copper water tank warms the cold well water up to room temp from the kitchen making the electric one not work so hard then too.I have a pressure tank in the cellar that is old that stays at around 40 ibs.ANDALSO tO JUST TURN THE HOT WATER FIXTURE A BIT SENDS COLD WATER into the tank-Does that cold water in the bottom of the tank aid in any cooling??

[Harold KestenholzParticipant]

These systems were like side-arm heaters at the turn of the century. A 1-inch pipe ran around inside the fire box of the stove, then out to a riveted tank sitting nearby. Water from the tank entered the bottom of the coil to continue back to the tank by the power of gravity (difference in weight due to temperature) so it was called a thermosyphon action.

The tank-in-the-wood (or coal) stove is more dangerous today as the water pressures are higher. Your feeling that another relief valve would be safer is intuition giving a warning. Place another relief valve 20 pounds higher than your normal water pressure in the line going to the waterheater downstairs and check or replace the T&P valve once per year. The solid fuel heater can turn all the water in the stove tank to steam, then overheat and burn the metal. When the fire starts to die out, cold water can enter rapidly to cause a tank failure in the stove.

The old pipe idea in the stove was safer, as the pipes had a smaller diameter than a tank, so could stand higher pressures. They also contained less water, so the steam propelled less metal. Maintaining a small fire in the stove sent a small amount of water through the pipe to heat the larger tank all day. As the average electric bill for a family is $800 per year. Saving half that by high risk is not worthwhile.

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