Rocket Stove Pool Heater Build and Testing

Steps

1. 1

   Step 1: Intro and planning

   Watch this part (0:53)

   In the previous video, I built a rocket stove from metal pipes to generate intense heat for a swimming pool. I tried adding insulation around the riser to hold heat in, but I noticed no big difference with or without it. Since the chimney radiates a lot of lost heat, I want to capture that heat by wrapping a hose around the pipe from bottom to top.

   I want to keep the bottom section unwrapped because that area needs to stay as hot as possible for the fire to burn efficiently. From the upper section, I can let water spiral upward through stainless steel pipes to preheat it before it enters the heat exchanger. I tried rolling an stainless steel hose inside the riser, but it only warmed the water by one or two degrees and caused too much airflow resistance in the chimney. Copper cannot handle fire and burns out in no time, so I needed a different solution.

2. 2

   Step 2: Explaining the heat exchanger

   Watch this part (2:10)

   The solution is a stainless steel frame where water enters, travels down the pipe, turns around at the bottom, and comes back up. To increase the surface area, we screwed vertical fins onto the pipe. These fins let the rising hot air pass through with very little air resistance so they do not block the rocket stove, while absorbing heat and transferring it to the water.

   When I tested running the stove at full blast, I could literally hold my hand above the chimney where before I could not even go near it because it would burn my hand. This means the metal frames absorb most of the heat generated in the rocket stove and pass it to the water. The water temperature is about four to five degrees warmer at this speed.

   What I used

   Item	Amount	Notes
   Stainless steel frame	1	Water goes in, travels down, turns around, and comes back up
   Fins	multiple	Screwed lengthwise onto the pipe to absorb heat without blocking airflow

3. 3

   Step 3: Testing the heat exchanger

   Watch this part (3:20)

   I discovered one drawback to this frame that I never thought about before, which is why testing is important. The fire inside is extremely warm, but it pushes in normal fresh air which contains moisture. Because the water-cooled frame inside has cold pool water running through it, the extremely hot interior combined with a cold frame causes condensation that drips onto the fire.

   Below 60 degrees you will always have this condensation, and I will probably not reach 60 degrees when pumping water at this speed. To minimize this, I want to make a spiral around the rocket stove so water enters at the bottom, circulates upward to absorb side heat, and only then goes into the frame above the riser.

4. 4

   Step 4: Explaining the spiral

   Watch this part (4:16)

   These flexible pipes are 3 meters long and can be ordered on AliExpress. Because they are ribbed, you can bend them into any desired shape. I want my water inputs and outputs at the front so the heater stands flat against the fence.

   What I used

   Item	Amount	Notes
   Flexible ribbed pipes	1	3 meter length ordered on AliExpress

5. 5

   Step 5: Building the outer spiral

   Watch this part (5:00)

   I can position this pipe at the front and secure it with a copper wire because copper can withstand the heat, then let it spiral upward. The first 3-meter length is now wrapped around the pipe and stops here. Now I take another 2.5-meter section to attach to it and continue upward.

   There are some spaces between the coils, which is fine because I want to build a cover over it and fill it with sand. By flaring one pipe slightly, the two pipes can slide into each other, then you sand them and solder them together with solder tin. Once these pipes are soldered, you must test them for water tightness by applying air pressure before winding them upward.

   What I used

   Item	Amount	Notes
   Flexible ribbed pipe	1	2.5 meter section
   Copper wire	1	Used to secure the pipe
   Solder tin	1	Used to solder the pipes together

6. 6

   Step 6: Building the housing

   Watch this part (6:08)

   I made the outer cover into one large square casing using four corner profiles and leftover plates we happened to have, and bolted them together. There are holes made at the top and bottom where the pipes come out nicely. A safety flexi is attached so the pipe does not get damaged.

   What I used

   Item	Amount	Notes
   Corner profiles	4	Used for the square casing
   Restant plates	multiple	Bolted to the corner profiles
   Safety flexi	1	Protects the pipe where it exits

7. 7

   Step 7: Filling with sand

   Watch this part (6:48)

   Next, I am making the bottom plate so the casing is properly sealed and closed off. I can also press aluminum tape along the bottom so sand grains cannot fall out and the sand stays inside. I sealed all seams and openings around the pipes and hoses using heat-resistant sealant rated up to 1200 degrees so no sand can escape.

   Store-bought sand is still moist and wet, but dried sand falls around the pipes much easier and fills all hollow spaces. Wet sand clumps together and acts like a sandcastle, which is not practical for filling a pipe enclosure.

   What I used

   Item	Amount	Notes
   Aluminum tape	1	To seal the bottom against sand leaks
   Heat-resistant sealant	1	Rated up to 1200 degrees to seal seams and pipe openings
   Sand	1	Store-bought dry sand

8. 8

   Step 8: First time heating

   Watch this part (8:00)

   Once the rocket stove is almost completely filled with sand, we can shake it so the sand settles down as much as possible. Then we fire it up to make the pipes and interior very hot, which evaporates the last bit of moisture in the sand. The sand will dry out, flow even better, and fill all the internal openings.

   While heating, it is helpful to shake it a few times, but watch out because the unit is hot and you can burn yourself. You can hear the deep, sucking humming sound coming from the rocket stove as it continuously draws in fresh air and fans the fire. You can see what the insulation does with the sand as the plastic on the outside can still just barely be touched before burning my hands.

   Warning

   The unit is hot during heating, so be careful not to burn yourself when shaking it.

9. 9

   Step 9: Placing the heat exchanger

   Watch this part (8:55)

   Now we reach the nice part where we can remove all the plastic. My youngest child, Tellich, gives great help by pulling off the plastic wrap. Every now and then you let the sand settle so the moisture escapes and the sand flows underneath everything.

   I refilled it with sand until it was nearly filled to the top.

10. 10

    Step 10: Test setup

    Watch this part (9:27)

    Now we can put the heat exchanger in its place. I am going to use a piece of pool hose to connect these two pipes together. For the test setup, a water hose runs from a submersible pump to the bottom intake.

    I used a piece of pipe as an adapter, sealed with sealant so it is waterproof, and it curls upward.

    What I used

    Item	Amount	Notes
    Pool hose	1	Connects the two pipes
    Submersible pump	1	Supplies water from the pool
    Pipe adapter	1	Sealed with sealant for the intake

11. 11

    Step 11: Testing the heater

    Watch this part (10:08)

    The water comes out, goes through another PVC pipe adapter and a flexible piece to make the turn to the heat exchanger. From the heat exchanger it goes through the pipe and back out, returning through this hose into the pool. The pool water is currently real cold at 24.9 degrees because of recent cold weather.

    Water goes in at the speed of the submersible pump, and the output reaches nearly 30 degrees. This means the water comes out six degrees warmer than it went in at the speed of a standard index pump.

    What I used

    Item	Amount	Notes
    PVC pipe adapter	1	For the return path
    Flexible hose	1	For making the turn to the heat exchanger

12. 12

    Step 12: Asking viewers to leave a like and subscribe

    If you enjoyed this video, please leave a like and click on the subscribe button. It really helps me out, and this way you are always up to date when new videos come out. I will see you in the next one.

13. 13

    Step 13: Takeaways

    • Adding external spiral pipes and an internal finned frame successfully captures waste heat from a rocket stove chimney.

    • Dry sand works better than wet sand for filling the casing because it flows easily around the pipes.

    • The heater raises pool water temperature by about 6 degrees at pump speed.

    • One rocket stove unit is sufficient for a 4 cubic meter pool, but larger pools will require multiple units.