Wood stove water coil, thermosiphoning, pressurized vs non pressurized

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Oct 8, 2012
I have a D.S. machine Energy Max 160 with the stainless steel water loop plumbed inside of it. I’m designing how I’m going to use it to put some heat out to my attached 2 car garage. I installed 20’ of hydrotherm hydronic baseboard along the wall of the garage and ran the ¾” copper pipe into the basement next to the wood stove. Does the thermal storage tank have to be a closed pressurized tank for thermosiphoning to work? Or can it be an open atmosphere tank? I have the room to put the tank within a few feet of the woodstove and elevated if necessary. I’ve heard that during the coldest days of the year burning this stove with the water loop will heat enough to sometimes cause the blow off valve on an 80 gallon storage tank to open. That being said I’m more interested in an open to the atmosphere storage tank, so there’s no risk of explosion, and then making the loop to the garage its own line with a pump to circulate it. So does anyone know if thermosiphoning does in fact work in an open system? I was thinking of utilizing a 275 gallon oil tank, turned upright on its end, pluming the wood stove hot out to the uppermost fitting on the side of the oil tank (which would be about 24" higher), plumbing the cold return from either the bottom most fitting (which would then have to rise 12” to mate with the cold in to the woodstove) or the next fitting up (which would be just about level with the cold in to the woodstove), and then cutting a section out of the top end of the oil tank to drop the line from the garage down into the hot water in the oil tank to extract the heat. Any thoughts?

It would look similar to this setup,


except instead of the tank pictured I would have an oil tank like this one,



New Member
Sep 9, 2015
I don't know what to tell you about the larger tank. I'm not sure the stove will make enough hot water to used as a boiler to heat a garage. I may be wrong about that ( idk how many gallons have to be produced to heat your garage) . the gravity system does work . I would elevate your tank so the bottom connection on tank is as close to level as poss to cold connection on stove coil. This is not mandatory but I feel you will be losing some capacity if the tank is considerably lower that the coil. My cold on tank is approx 8 inches below the coil. It works but I feel it would be better if it was a little higher. Good luck


Minister of Fire
Apr 16, 2012
Northern Maine
If you want to thermosyphon, I'd go with an open system on a stove. Much safer IMHO. Can't speak of how much heat you will make.

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