The Hydra
Three outputs from a single fire: thermal mass for the room, a thermosiphon loop for hot water, and a thermoelectric module trickle-charging small devices off the same heat.
Why the name
Named for the Hydra of Greek myth — one body, many heads. Here it's one firebox feeding three separate outputs instead of one, the same many-from-one shape.
A single firebox stacked for three outputs: thick stone thermal mass for radiant space heating, a copper coil thermosiphon loop to a gravity-fed hot water tank, and a Seebeck-effect thermoelectric generator (TEG) module mounted between firebox-side heat and a cooled surface — using the water loop as the cold-side heatsink — to trickle-charge phones/USB devices or run small DC loads off the same fire.
The Three Outputs
- Thick stone thermal mass — radiant space heating.
- Copper coil thermosiphon loop — gravity-fed hot water, no pump required.
- Seebeck-effect TEG module — trickle power off the firebox-to-water-loop heat differential.
Safety Corrections — Required, Not Optional
An earlier version of this water loop (a bare closed-loop copper coil in the firebox with only an air-release vent and a purge valve) is a real, documented hazard: without a properly sized, ASME-rated pressure/temperature relief valve, a blocked or overheated coil can cause a steam explosion — a real cause of injury and death in DIY wood-stove water heating setups. This build corrects that:
- The water loop must be open/vented to atmosphere, OR a closed loop with a certified, correctly sized ASME-rated P&T relief valve — never just an air-release/purge valve alone.
- The TEG module's cold side must maintain a reliable heat differential (a water-cooled backing plate) to avoid module damage.
Real Capability — Don't Oversell It
TEG output here is phone/power-bank scale only, not appliance scale. Real use case: charge a power bank (also toppable via solar off the 4-wheeler) from the cabin fire — enough for a reading light or a phone the next morning in a tree stand. Caption this accurately whenever it's referenced elsewhere on the site; it's a trickle-charge bonus riding on a heating system, not a home power plant.