Wetbacks use heat from a wood or pellet burner to heat water. While expensive to install, they make sense if your burner runs most days in winter, especially with cheap or free firewood.

Since wetbacks can cause water to boil, they are usually low-pressure and require a tempering valve to keep water below 50°C. Some mains-pressure cylinders have built-in heat exchangers, allowing indirect heating from a wetback system.

If your property is under two hectares, your burner must meet National Efficiency Standards with the wetback attached.

Wetbacks pair well with solar water heaters, using the burner in winter and solar in summer.

Main benefits: efficient use of an existing appliance, cheap to run with low-cost firewood.

Main drawbacks: expensive to install, dependent on cylinder and burner type/location.