How wetbacks work
Heat from the combustion process is used to heat water jackets installed within the firebox.
Water is circulated through the water jackets and then through pipes to the storage heater.
Older wetbacks may simply consist of pipes which pass through the firebox of a wood burner, wood stove or, in some cases, through older style open fires.
Most wetbacks circulate the water through a thermosiphon effect (i.e. warmer water rises and cooler water falls, creating a natural flow through the water jacket within the solid fuel burner).
As a consequence, the hot water cylinder should be