A fire coil water heater, sometimes referred to as a water heater coil or tankless coil heater, is a type of on-demand water heating system that uses heat from a solid fuel source—like a wood stove, coal stove, or outdoor boiler—to heat water for domestic use. It’s a simple yet highly effective way to harness combustion heat to provide hot water without electricity or gas, especially in off-grid or rural settings.
What Is a Fire Coil Water Heater?
A fire coil is essentially a coiled metal pipe—usually made of copper or stainless steel—that is placed inside or around a firebox (such as in a wood stove, furnace, or fire pit). Cold water enters one end of the coil, absorbs heat from the fire, and exits the other end as hot water, ready for use in sinks, showers, or even radiant floor heating systems.
This type of water heater is particularly popular in wood-burning stove systems used in cabins, rural homes, off-grid properties, and emergency situations.
How It Works
Installation: The coil is mounted inside the firebox or stove chamber. Some models can be fitted externally, surrounding the stove or boiler flue.
Water Flow: When the fire is burning, cold water is circulated through the coil.
Heat Transfer: The intense heat from the fire heats the coil rapidly, and this heat is transferred directly to the water.
Hot Water Output: The heated water exits the coil and is directed to a storage tank or directly to the plumbing system.
A gravity-fed system or a circulating pump can be used to move the water, depending on the setup.
Key Benefits
Energy Efficient: Utilizes heat already being produced for home heating or cooking.
Eco-Friendly: No need for gas or electricity if a fire is already burning.
Ideal for Off-Grid Living: Perfect for cabins or rural homes without access to conventional utilities.
Simple Design: Fewer components mean less maintenance and fewer breakdowns.
Important Considerations
Overheating Risk: Without proper controls, water in the coil can become dangerously hot. Always include temperature and pressure relief valves (TPRVs).
Storage Needs: A holding tank or tempering tank may be required to regulate water temperature before use.
Not Always Instant: Heating depends on the intensity of the fire and the flow rate of water.
Installation Expertise: Requires careful integration with stoves and plumbing to avoid hazards or inefficiency.
Backflow Prevention: It's important to include check valves or air gaps to prevent hot water from pushing back into the cold supply.
Applications
Cabins and Cottages
Off-Grid Homes
Wood Stove Water Heating Systems
Emergency or Backup Water Heating
Greenhouses or Outdoor Baths
Safety Tips
Always use high-temperature rated materials (pipes, valves, fittings).
Insulate water lines to preserve heat and prevent burns.
Install a mixing valve to moderate water temperature and avoid scalding.
Use a thermal expansion tank if connecting to a pressurized system.
A fire coil water heater is a smart, sustainable, and cost-effective way to provide hot water using wood heat. With proper planning, safety measures, and maintenance, it can serve as a reliable system for both everyday use and off-grid living. Whether you're heating water for a rustic cabin or building a self-sufficient homestead, a fire coil system offers simplicity and efficiency with minimal fuel costs.
