Wood-stove flue water heater (thermosiphon coil)

A copper coil wrapped around a wood stove's flue pipe, thermosiphon-fed to a water heater tank, captures waste heat from a stove already burning for space heating to also heat domestic water, at no extra fuel cost. A distinct mechanism from both the solar thermosiphon heater and the compost-coil preheater: the heat source is flue gas, most productive exactly when solar gain is lowest, winter, when the stove runs most.

Cost
Low
Upkeep
Occasional
Skill to build
Intermediate
Lifespan
15-25 years for the copper coil before flue-gas corrosion or soot fouling degrades performance
Embodied carbon
Low
Space / material use
Low
Output timing
Weather/time-dependent
Skill to repair
Intermediate
Regulation (FR example)
Flue installation follows DTU 24.1. Chimney sweeping is compulsory (typically once or twice a year) under the departmental sanitary regulation, and insurers generally require proof. Some communes restrict wood burning under an air-quality plan.

Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.

What your site needs

Requires an existing wood stove with an accessible flue pipe; soldering competence to install

Inputs

Outputs

Sources

Tutorials

What this page does not tell you

No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.