Generally there are so many projects that a homesteader can do that benefit from warm water growing conditions. Tilapia and catfish both thrive in water that is at least 28°C (82°F) and as the season comes to an end, the drop in temperature can curtail the last growth spurt. Plants like rice also thrive in a warmer environment. To finish off my fish and rice growing cycle, I have found a wood fired water heater helps me lift the temperature substantially for two to three months, allowing growth right into winter. And making the pond pleasant to swim in and thrive on cold winters days.
The following is a DIY guide on how to fashion a crude but effective wood fired water heater out of an old drum, a piece of chimney pipe and a bit of 15mm (1/2”) copper pipes and a few elbows.
I started off by cutting the pipes to a length that would fit inside the drum.
Then I placed the pieces on a table and began attaching compression elbow fittings onto each piece. It really helps to mark the tightened nuts with nail polish or a pen. I forgot to tighten a few properly and this created problems later.
Next I cut small pieces of copper pipe to create the joins to create the first layer of the heat exchanger.
Attaching the second layer of the heat exchanger is a bit fiddly and requires a few longer connector pipes.
I placed the whole heat exchanger in the roof of a barrel, attached a small chimney and then used the barrel lid to create an air flow controller. Light fire with the barrel lid open. Once burning and smokeless, close the door and it breaths through the three holes, and just slowly burns.
Large logs placed inside will burn through the night, and during the day it is easy to refuel and put a few big logs in allowing the system to constantly heat the pool. The pool fountain pump circulates water into the heat exchanger at a rate of about 1200-1500l/h (320-400 gallons an hour).
When the pool temperature drops to 16°C (60°F) I normally start heating. The pool has a volume of approximately 6000l (1585 gallons) and the rice paddy about 1500l (396 gallons).
At the flow rate I use the system starts off by heating the water about 4°C, and as the fire gets going and the coals form, you will find that you tend to start lifting the temperature a bit more.
There is a fine line between getting the system to work perfectly and creating a sauna for your fish (soup). I tend to try and keep the outlet flow below 40°C (104°F) as this temperature just causes trouble, deoxygenates your water, and can hurt the roots of the rice in the rice paddy.
Typically, I find it is pleasant to get in a steady state where a nice bed of coals burns in the heater, and your pool fluctuates between 25°C (77°F) and 32°C (90°F).
This keeps the fish and plants in the system healthy and doesn’t burn through too much wood.
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Cool except…. copper is toxic to fish. https://fishhistopathology.com/home/2020/09/04/copper-toxicity-in-fish/
I was worried about the copper as well. I am trying to do something at the moment using stainless steel beer kegs.