This project was a smashing success! Every hour that I run this, it saves us 1500 watts of grid electricity per hour which is what our 'old' pond heater consumed. The sky is the limit on this too. I could route part of this to heat our garage, my workshop, etc. Next year, I plan to route a leg of this to heat our green house - fresh veggies all winter!
Step 1: Aluminum Vs. Copper
I want to pause here for a moment, in case it isn't evident why I chose to use Aluminum tubing over Copper tubing - the same reason you don't throw copper coins into a fish tank.. using copper tubing will kill the fish.
Step 2: The Coil Becomes a Heat Exchange!
Three other points of interest;
1. There is a soft clamp on the far end of the tubing, just to keep it from flopping around.
2. A large 'C' clamp as an axis point to create the 1st bend towards the coil. I found that by pulling the tubing around the pipe, instead of smashing it worked just fine & didn't kink or flatten at all. I took my time, kept tension on the lot & pulled the leading edge until I'd made what I wanted.
3. The edges of the larger sprinkler pipe [that I am winding the aluminum tubing around] are quite sharp, even after filing them down a bit. It is far easier to put on a pair of gloves than it is to rush off to the hospital for stitches because you've laid your fore arm or wrist open on a jagged piece of metal. I have done it myself & it's always the 'oh this will just take a minute' job that does it. Always, be careful. Please!!
Step 3: The Finished Coil
Step 4: In Through the Clean Out
The 2nd photo is a little closer shot & shows the screw I used to wedge the whole assembly in. I replaced this with a pole which worked out even better.
NOTE!!! If you are doing this be sure to either have the water running when you insert the coil into the chimney or DO NOT have a fire burning!!! I had the assembly laying on the ground & a siphon was running water through it - I did not realize this & thought the pump was on. Once I slid it up into the stove pipe, it did not take two minutes to blow a plume of steam out the other end of the coil. A few more minutes would have melted the aluminum & if then, the water was turned on with the coil melted - the possibility of a steam explosion/burn/incident/nastiness can occur. If the walls of the coil have sprung a leak, then when the water flow resumes, if any of that goes DOWN the stove pipe & into the fire box - there is no telling how bad it could be so be durn careful.
I purged all the air out of the lines & have both the intake & the discharge well under the surface of the pond water. That way, even if we suffer a power failure the water can rock back & forth without causing any real damage.. hopefully.
Step 5: Inspection Time
The black area on the wood plug is not charred as much as it is stained; a very unexpected thing happened. The cold water running through the coils causes a considerable amount of condensation to form & drip out from the bottom of the assembly. I thought that once the chimney came up to ambient temperature that this would cease but that was not the case. The hotter the fire the more condensation would drip.. it's basically 'liquid smoke' but you won't catch us cooking with it, lol.
Step 6: Temporary Plumbing
So here's the data:
The other night [test #3] it was 31 F [-0.55 C] outdoors. The water temperature at the intake was 40 F [4.44 C] and at the discharge it was up 12-15 degrees to about 63 F [17.22 C]. By morning, which was about ten hours later, overall the pond temp was up 28 degrees to a balmy (in fish terms) 68 F [20 C].
Even without having the PEX tubing insulated, I am only loosing 3-4 degrees between the heat exchange coils and the final pond discharge 25' [7.62 m] away. When spring comes I will decide whether to bury the PEX tubing or to plumb all but the ends in PVC. Regardless, this project was a definite success! Every hour that I run this, I save at least 1500 watts of grid electricity - that is what our 'old' pond heater used and then it only kept the water just above freezing.
Step 7: FOLLOW UP ESSAY:
I also noted that as the creosote built up on the coil, the less efficient it became. Fig 1 shows the heat exchange coil after being removed from the stove pipe and Fig 2 after it was pressure washed. Fig 3 is a close up of same to show pitting on the coils. I suspect this is due to the caustic nature of hardwood ash [see 'lye']. This was one of many safety issues that presented itself during this experiment.
TO ANSWER QUESTIONS RAISED IN EARLIER COMMENTS:
I have come to realize that in order to present one idea as an Instructable, I will have to do 2-3 others to explain how I got there in the 1st place. The wood stove we installed is not like the wood stove I grew up with, this one is a bit small & didn't draw well, initially we had to build a small fire to heat it up before we could get real. After speaking with our chimney people [yes, we're inspected yearly] I made some alterations to the stove & it is now an amazing thing! It doesn't burn the wood so much as it incinerates it, the ash left behind from a whole rick of wood can be fit into a shoe box. Also, to the person that said 'new chimneys need to have a temp of 700 deg to operate correctly' I'd really like to know what you base that on because the fire box doesn't even get that hot. After the changes I made to the stove and with no fire burning, I saw the draft from up the chimney blow his ball cap off his head while standing on my roof.
Generally speaking, yes it's true that so long as the water doesn't freeze solid the fish will be fine - I know that. However, not all the fish can handle the drop in temperature - we add two placos every year to help keep the algae down. When the temp gets to 65 F [18.33 C] the placos are the 1st to die and by end of season, they are quite large. This was for a real life experiment and heating the greenhouse 1st would have taken too long to see results, the Instructable wouldn't have been out till this summer or later. Although I did state that 'I could run a leg of this to heat...' that as it turned out, was wishful thinking. Due to the height of the heat exchange in the chimney, the flow at the pond discharge was slight. I have photos but suffice to say, I could fill up a coffee mug at the sink 2x before I could from the pond discharge. Now that said, do not think for a moment that this is our main pump/filter line, that is a totally different system, so let's not get off on a tangent there.