Hooking up a DHW tank to a wood stove. Did anyone try this?
- Thread starter Don2222
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I had a Clayton wood furnace with a factory option water heating loop. It was a 3/4 stainless pipe loop that was positioned as this guy is doing, except it was inside the firebox. I wanted more and supercharged it by adding another of those loops in series on the return to the tank, positioned horizontally inside the top of the firebox. That setup made serious hot water! It could heat my 80 gallon tank to 120 F from 50 in a few hours, and could hit 180F, or higher I'm sure if I wasn't getting nervous at that point. If I was running the furnace hard sometimes I'd fill the big soaking tub just to knock the temp back down before an overnight burn (twist my arm a little harder to take a soak in the steaming tub on a really cold evening)!
I think you can still buy those US Stove hot water loops for a reasonable price if you have a need.
The guy in the video is duplicating what used to be an option on the Kuuma furnace (pre EPA testing) only with 1/2 instead of 3/4 and fewer back and forth passes on the pipe, so it's not crazy. Tips for him would be more passes, and the more you elevate the tank in relation to the stove, the better it's going to work. The solder will be fine as long as there is water in the pipe, as the water will keep the solder cool enough. See the vids of boiling water in a campfire with a plastic water bottle.
Valving the heating loop and any goofing around with the pressure relief in the heater is not something I would do. Another terrible idea is to disconnect the water heater and cap off the heating loop on the stove. I'm aware of a couple of instances where that has resulted in the burning contents of the woodstove being scattered about the room. I know one was a secondhand stove and the second buyer was unaware of the capped off heat coil that apparently still contained some water. Any heating of water that is contained or under pressure, or could possibly get that way, should be approached with a great deal of caution!
I think you can still buy those US Stove hot water loops for a reasonable price if you have a need.
The guy in the video is duplicating what used to be an option on the Kuuma furnace (pre EPA testing) only with 1/2 instead of 3/4 and fewer back and forth passes on the pipe, so it's not crazy. Tips for him would be more passes, and the more you elevate the tank in relation to the stove, the better it's going to work. The solder will be fine as long as there is water in the pipe, as the water will keep the solder cool enough. See the vids of boiling water in a campfire with a plastic water bottle.
Valving the heating loop and any goofing around with the pressure relief in the heater is not something I would do. Another terrible idea is to disconnect the water heater and cap off the heating loop on the stove. I'm aware of a couple of instances where that has resulted in the burning contents of the woodstove being scattered about the room. I know one was a secondhand stove and the second buyer was unaware of the capped off heat coil that apparently still contained some water. Any heating of water that is contained or under pressure, or could possibly get that way, should be approached with a great deal of caution!
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I have seen several systems like this and this has been thought out better than many but I will point out some issues
1. Scaling of the heat transfer loop. Some areas have soft water and scaling may not be an issue, but in many places, the loop will scale up as fresh water is being constantly put through it. Scaling happens slowly and at some point, he will not be getting the flow he needs, long before that his well pump (assuming he has one) will be chewing up a bit of extra power to push the water through the necked down piping. If scaling is an issue I think he will find that his system loses effectiveness in heating his hot water. Scaling can be dealt with by acid washing but few homeowners know how or care to routinely descale heat transfer coils. When it finally plugs up is the end of the experiment for most people.
2. I see he has a safety gate and a couple of toddlers in the background. At some point, the gates go down and kids are closer to the equipment. I believe plumbing code requires that all safety relief discharges get plumbed to within 6" of the floor. With the current setup, both reliefs are not plumbed to the floor, should they release when an adult is around, they may get it in the face or the torso while a child could get sprayed all over. I know copper is expensive but not a place to skimp.
3. He didn't go into details on the tempering valve. If all the home hot water supplies are all equipped with antiscald valves, it may be less of an issue, but the tempering valve would need to be the type that has an integral anti scald function so that the flow stops if the outlet temp exceeds 140F. Many tempering valves do not have that feature, and they can fail in way that scalding water can be sent to the fixtures. (so this one needs more information to confirm if the valve has antiscald).
4. The biggest issue is where does the excess heat go if there is no demand for water but a big demand for space heat (like a power outage). This seems to be the big flaw in these systems. Yes, I see that he has unions installed to disconnect the system but would a future home owner know and have the tools and strength to break them? The far more likely scenario is the heat from the stove going into the hot water tank will exceed the hot water going out of it to the house and the relief valves will do their thing and open. Once a relief opens, it usually leaks when it closes until scale seals it up or someone not familiar with the system just closes the valve to stop the leak and the coil boils out. Copper pipe is good for 400F so the empty pipe next to the stove will probably not fail but solder is only rated to 250F so the coil joints will eventually fail.
1. Scaling of the heat transfer loop. Some areas have soft water and scaling may not be an issue, but in many places, the loop will scale up as fresh water is being constantly put through it. Scaling happens slowly and at some point, he will not be getting the flow he needs, long before that his well pump (assuming he has one) will be chewing up a bit of extra power to push the water through the necked down piping. If scaling is an issue I think he will find that his system loses effectiveness in heating his hot water. Scaling can be dealt with by acid washing but few homeowners know how or care to routinely descale heat transfer coils. When it finally plugs up is the end of the experiment for most people.
2. I see he has a safety gate and a couple of toddlers in the background. At some point, the gates go down and kids are closer to the equipment. I believe plumbing code requires that all safety relief discharges get plumbed to within 6" of the floor. With the current setup, both reliefs are not plumbed to the floor, should they release when an adult is around, they may get it in the face or the torso while a child could get sprayed all over. I know copper is expensive but not a place to skimp.
3. He didn't go into details on the tempering valve. If all the home hot water supplies are all equipped with antiscald valves, it may be less of an issue, but the tempering valve would need to be the type that has an integral anti scald function so that the flow stops if the outlet temp exceeds 140F. Many tempering valves do not have that feature, and they can fail in way that scalding water can be sent to the fixtures. (so this one needs more information to confirm if the valve has antiscald).
4. The biggest issue is where does the excess heat go if there is no demand for water but a big demand for space heat (like a power outage). This seems to be the big flaw in these systems. Yes, I see that he has unions installed to disconnect the system but would a future home owner know and have the tools and strength to break them? The far more likely scenario is the heat from the stove going into the hot water tank will exceed the hot water going out of it to the house and the relief valves will do their thing and open. Once a relief opens, it usually leaks when it closes until scale seals it up or someone not familiar with the system just closes the valve to stop the leak and the coil boils out. Copper pipe is good for 400F so the empty pipe next to the stove will probably not fail but solder is only rated to 250F so the coil joints will eventually fail.
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