Heating 5 gallon bucket of water with a wood stove

My dad said when his Boy Scout troop would go camping they would have a nice fire going in camp, would set a 5 gallon bucket close to the edge and run a copper pipe from the bucket through the fire and back into the bucket. He said the fire would cause a natural circulation pulling water out of the bucket into the fire then putting hot water back into the bucket on the other end.  

1. Is this accurate?
2. If so, how does the "circulation" know which direction to go along the copper pipe? How does it know to flow into end of pipe A and out end of pipe B and not the other way around?
3. If this does work, is there enough draw from the natural "circulation" to actually pull the water from the bucket up to the coil around the stove pipe? I understand there is enough pressure pushing the heated water up the pipe and out the other end.  

Most of the designs I've seen with wood stoves seem to have the tank high enough so the water flows from the water tank into the copper pipe by way of gravity (i.e. tank is slightly higher than the intake pipe on the copper coil). Is this required, or could I have a copper coil on my stovepipe, set the ends into a 5 gallon bucket off to the side and let the "circulation" process will do the rest?  

Currently I heat water 1 gallon at a time in a pot on top of the stove and dump it into a 5 gallon bucket (repeating until the bucket is full). Then I use a battery operated shower attachment to take a shower. I'm trying to find ways to heat the entire 5 gallon bucket (or even water in a 20 gallon soak tub) all at once without all the manual maneuvering (and the extra time it takes to do 1 gallon at a time).

In the summers I've found setting out plastic milk jugs full of water on the dock will produce all the hot water I desire by around 1pm. But in the winter it's a different story.  

Thoughts?

IH

Search for the term Thermosiphon. The heating loop needs to be connected to the bottom and top of the storage tank, and the tank should be elevated above the loop. It works on the principle of heated fluids being less dense - hence why hot air rises. Hot water does the same thing, and as it is heated and rises to the top of the tank, it pulls denser cool water from the bottom.

I made a solar collector with some old windows and black poly hose that would heat up about 5 gallons of water to 140 degrees on a sunny day. A wood stove based system would also be quite easy to put together.

Carl Nystrom wrote:Search for the term Thermosiphon. The heating loop needs to be connected to the bottom and top of the storage tank, and the tank should be elevated above the loop. It works on the principle of heated fluids being less dense - hence why hot air rises. Hot water does the same thing, and as it is heated and rises to the top of the tank, it pulls denser cool water from the bottom.

I made a solar collector with some old windows and black poly hose that would heat up about 5 gallons of water to 140 degrees on a sunny day. A wood stove based system would also be quite easy to put together.

I'm doing some reading here and I just want to double check that I have this right. The copper coil experiences the heat from the stove pipe which begins the siphon up the copper tubing (I assume the copper coil and all the hoses should be primed with water) giving the direction of the water to go up through the copper coil and out the end into the 5 gallon bucket.

Wouldn't this process of siphon simultaneously create a vacuum below in the copper pipe, causing the water from the other in to be drawn into the hose from the bucket? Where, as long as the heat source continued to heat the water the water would continue to circulate from the bucket, through the copper coil and back into the bucket?

If so, how much of a draw is there? Is the requirement to have the bucket higher than the coil two ease the draw from the bucket into the coil or is the siphon not strong enough to say pull the water up 1 or 2 feet? (say bucket is sitting on the floor and the coil is 2 feet above the level of the bucket)

With my dad's (possibly erroneous) example, the bottom of the bucket and the campfire are at the same level. The copper tubing it placed into the top of the bucket and into the water. The siphon then has to pull the water up (6 inches) out of the bucket, down to the fire, then push it back up the other end of the pipe and back into the bucket? But this is probably opposite of how it works, probably pushing first then pulling.  

Is this possible or was he most likely exaggerating (or possibly failed to mention that he put the bucket on a chair or small table, etc)?

IH

The first example I know will work. The second might work. The third one likely will not. The part you are heating could be a coil instead of a straight line. The effect relies on the water to have a gradual uphill path to the top of the collector. It is a very slow movement of water, but it can move a lot of heat all the same.

If the lines go in over the top, it would be imperative that they were fully primed. In theory I think it could work, but I have never tried it that way. A siphon tube at the bottom of the container should behave as though it were connected to the bottom, only with the addition of some friction loss. Since the driving force is small, you want to minimize friction losses. You want to make the water path as streamlined as possible - avoiding sharp bends in favor of gradual curves wherever possible.

It would not be hard to test a few configurations, but soft copper pipe in larger sizes is kinda pricey if it ends up not working. At any rate, post what you find if you give it a go.

Carl Nystrom wrote:

The first example I know will work. The second might work. The third one likely will not.

It would not be hard to test a few configurations, but soft copper pipe in larger sizes is kinda pricey if it ends up not working. At any rate, post what you find if you give it a go.

Hey Carl,

Thanks for posting the diagram. This is exactly what I'm trying to determine. The first image would be more difficult for my immediate circumstance since the wood stove sits up about off the ground about 10-16 inches. The coil another 12 inches higher at the base. I would really like to put the bucket on the ground next to the stove and just drop the lines into the water and let it work.

I see your difference between image 2 and 3 with the differing depths of the lines. I will order some copper tubing for this spring and will try it out as soon as I set up camp for the summer. It currently takes about 1 hour (maybe 1.5) to heat up 5 gallons doing 3 sets in the smaller pot and transferring water by hand. I would think a system like #1 or preferably #2 would do the job in the same or less time (finger's crossed). My aim would be to lessen the work of sitting around waiting and transferring water 3 times + shortening the time it takes to heat the water (or keeping the length of time and maybe increasing the amount of water to use, such as going form 5 gallons to 10 gallons).  

I will do some experimentation and report back with some pics and maybe even a video. I'll post it to this thread when I do.  

And thanks again for the info.

IH

All three examples would work, as long as the piping is all primed. The over-the-top ones would have more friction and work slower, and the third would be less effective since it would be circulating the hottest water instead of pulling up the colder water from the bottom. The hot return would not have to rise from the coil. The whole system would be more efficient the higher the bucket was located above the coil. If the bucket was below the coil, there would be a point where there would be insufficient push to move the hot water down to the bucket.

I would put the 5-gallon bucket on a bench or whatever above the stove, even at the ceiling if it can be used without moving it from the heating location. Then all you have to do is lift the bucket of cold water up or fill it with jugs, and the heating will be quickest and most effective. In this case I would put fittings in the top and bottom side of the bucket so you don't have to mess with priming and can draw off the heated water easily. A length of insulated hose to the shower location would make for maximum convenience.

Glenn Herbert wrote:All three examples would work, as long as the piping is all primed. The over-the-top ones would have more friction and work slower, and the third would be less effective since it would be circulating the hottest water instead of pulling up the colder water from the bottom. The hot return would not have to rise from the coil. The whole system would be more efficient the higher the bucket was located above the coil. If the bucket was below the coil, there would be a point where there would be insufficient push to move the hot water down to the bucket.

I would put the 5-gallon bucket on a bench or whatever above the stove, even at the ceiling if it can be used without moving it from the heating location. Then all you have to do is lift the bucket of cold water up or fill it with jugs, and the heating will be quickest and most effective. In this case I would put fittings in the top and bottom side of the bucket so you don't have to mess with priming and can draw off the heated water easily. A length of insulated hose to the shower location would make for maximum convenience.

Interesting. Yes, there is a "possibility" that I could implement a higher bucket, but it would have to be outside of the shelter (where the wood stove is). The problem here would be possible freezing of the pipes when temps fall (doesn't happen often or for long periods but does occur a few times each winter). I could bury the tank (still above the stove) and then pipe it down in buried lines to a shower stall.

This would be a lot of effort though. I would much rather have just a portable bucket or a couple buckets to heat. In the winter it won't be a problem on time since the stove will be going throughout the day so I can lounge comfortably in the shelter. But in the summer that might be an issue (though this would be when I could start heating water in a solar system down on the dock in full sun).  

Sounds like the key to making each of these scenarios work is priming the coil with water. I think I like the middle one the best so it would pull in the cold water first.  

IH

I think 1/2" soft copper tubing would work fine for a 5-gallon range of volume, and with a good fire you could probably heat the water in an hour or so with no tending (aside from the fire ).

If you want a portable system, make the coil such that it can be stored inside the bucket, with flexible hoses to connect it.

Glenn Herbert wrote:I think 1/2" soft copper tubing would work fine for a 5-gallon range of volume, and with a good fire you could probably heat the water in an hour or so with no tending (aside from the fire ).

If you want a portable system, make the coil such that it can be stored inside the bucket, with flexible hoses to connect it.

Sorry, portable as in being able to move the bucket around, i.e. heat it in the shelter where the stove is and then carry the bucket out to the deck for the shower. The coil and stove would be permanent in the shelter. I would prefer to only have one fire source for all my needs (shower, cooking, heating, etc). My camp doesn't move around.

IH

Isaac Hunter wrote:
Currently I heat water 1 gallon at a time in a pot on top of the stove and dump it into a 5 gallon bucket (repeating until the bucket is full). Then I use a battery operated shower attachment to take a shower. I'm trying to find ways to heat the entire 5 gallon bucket (or even water in a 20 gallon soak tub) all at once without all the manual maneuvering (and the extra time it takes to do 1 gallon at a time).

In the summers I've found setting out plastic milk jugs full of water on the dock will produce all the hot water I desire by around 1pm. But in the winter it's a different story.  

Thoughts?

IH

That's pretty neat idea with the milk jugs; I'll have to give that a try!

I won't address the stove thermosiphon portion of your question in full, because water coils + fire = potential for "boomsquish" if inappropriately designed.  Basically any time you have copper tubes of hot water and a strong heat source, a temperature and pressure relief valve system is in order to save your life should the water accidentally reach boiling conditions.

If you have the time, you can check out this top-notch video from Living Web Farms' YouTube channel which goes into great detail on hot water from stoves.


They also have excellent videos on DIY solar water heat collectors and plumbing in general.

For a super safe and portable option that meets your stated goal of heating 5 gallons of water all at once, consider one of these products, which go directly on top of a stove.  Maybe you could heat it up to the temperature of your desire, and then drop the battery operated intake, routed outside to a shower area.  Regardless, keep us posted on what works for you!

*Full disclosure: I have invested in Camp Chef's parent company, Vista Outdoors Brands because I think such products are cool.

George Yacus wrote:
That's pretty neat idea with the milk jugs; I'll have to give that a try!

It actually works quite well since the water amount in each jug is only a gallon. I tried several years before with a large black blister bag especially for solar showers and it wouldn't heat the water at all given the large quantity and the limited sun, cooler temps and near constant breeze. But the milk jugs are quite effective. 4-5 hours and I have nice warm water to use. Too bad it doesn't work in the winter!

George Yacus wrote:
I won't address the stove thermosiphon portion of your question in full, because water coils + fire = potential for "boomsquish" if inappropriately designed.  Basically any time you have copper tubes of hot water and a strong heat source, a temperature and pressure relief valve system is in order to save your life should the water accidentally reach boiling conditions.

As I understand it, wouldn't this system I'm proposing not be under any pressure since the "tank" (5 gallon bucket) has no lid or no pressure within it to trap the steam? I wouldn't think there would be any risk here of exploding. I get it if I were using a conventional hot water heater tank.

George Yacus wrote:
For a super safe and portable option that meets your stated goal of heating 5 gallons of water all at once, consider one of these products, which go directly on top of a stove.  Maybe you could heat it up to the temperature of your desire, and then drop the battery operated intake, routed outside to a shower area.  Regardless, keep us posted on what works for you!

I have considered this. It is much easer to implement and is really just a larger capacity to what I'm doing now with a 1 gallon pot. I'm wondering if such a pot on top of the stove would make it potentially top heavy, plus 5 gallons is a lot to pick up and move around at that height. I've looked at these large pots (not this specific brand) and all the reviews are terrible. I'll check out this one in particular. Thanks for the tip.

IH

If you want to carry the hot bucket out to the deck, then I suppose you need the over-the-top style of coil assembly. Is your stove a lightweight/narrow design? If so, a bucket on top would obviously be unsafe. I would have a table or stool at a convenient height for picking up a bucket, so you don't have to bend down to do it and so the thermosiphon will be as easy as possible. A coil could give more heat transfer area so probably quicker heating than a big pot. A shutoff valve on the cold water side of the loop (only) could ensure that the piping stays primed. I would add a funnel-type end to the cold side to make priming easy. The open system you have described would indeed not be subject to explosion, just possibly a boiling/steam jet in case of overheating.

Glenn Herbert wrote:If you want to carry the hot bucket out to the deck, then I suppose you need the over-the-top style of coil assembly. Is your stove a lightweight/narrow design? If so, a bucket on top would obviously be unsafe. I would have a table or stool at a convenient height for picking up a bucket, so you don't have to bend down to do it and so the thermosiphon will be as easy as possible. A coil could give more heat transfer area so probably quicker heating than a big pot. A shutoff valve on the cold water side of the loop (only) could ensure that the piping stays primed. I would add a funnel-type end to the cold side to make priming easy. The open system you have described would indeed not be subject to explosion, just possibly a boiling/steam jet in case of overheating.

A table might work. Yes the stove I currently have is narrow and so is the next stove I plan to get (though it is somewhat larger than the current one). Yes, if I'm moving the container around then it would have to be over the top style. I would love to have a small soak tub (quite small) next to the stove, but there is not room vertically (low ceiling) to raise it up above the height of the stove/stovepipe (where the coil would be). The soak tub would be fixed in position with a drain running out of the shelter (underground) and down the hill, possibly to a gray water collector to use on the garden or tree seedlings, etc. But, this would require some additional digging that I'm not certain I'm willing to commit to.  

I'll definitely have to do some hands on testing to see what works best.

IH

I've updated my plans for making hot water and had a few questions before I start ordering supplies.

1. I would like to attach the exit pipe that puts hot water back into the tank around the middle of the tank (rather than at the top) so the copper pipe stays primed even if the water level is down several inches. Would this arrangement (input from tank (cold water) at the bottom and the exit (hot water) in the middle) still heat all the water in the tank (even when full)?

2. Are there any issues (such as wet soil) with having the tank partially buried?  

3. I've increased the tank size from 5 gallon to 20 gallon? This system would automatically heat the water whenever there is a fire going in the shelter without any manual inputs (other than adding water to the tank). The stove would be going all day in winter and for a few hours around 10am and then again around 2pm for a few hours while cooking, etc. in the summer.  

4. The lid on the tank will not be sealed, but loosely sitting on top. Would there be a problem with pressure? I could put a 3 in by 3 in hole on the top of the lid with a screen that would allow steam/pressure to escape while also allowing the tank to fill when it rains (my current 55 gallon barrel on the deck has a crack in the lid and fills up with just a short rainfall.  

Thanks for any info.

IH

If the tank is simply buried, I think the soil will wick away all your heat.  If it's insulated it's a different story.

Why not just put some stock pots (2-4 gallons) on your stove to keep water warm all the time?  And give you some thermal mass.

I wonder if your dad's system had one half of the copper pipe outside the fire and the other half in the fire.

Mike Haasl wrote:If the tank is simply buried, I think the soil will wick away all your heat.  If it's insulated it's a different story.

Why not just put some stock pots (2-4 gallons) on your stove to keep water warm all the time?  And give you some thermal mass.

I was thinking this might be a problem if not insulated.  

I was looking at pots. I currently use a pot now that holds 1 gallon of water. It works well. If the pot is too tall it could be a spill hazard. But I might be able to get away with a 2 gallon pot.  

IH

In Scandinavia, we have special wood heated water tanks. Insulated, water stays hot for up to 24 hours. They are not even too pricey.

https://www.takkauunit.fi/tuotteet/kiukaat/kota-muuripadat/kota-80-l