Wetback

Wetbacks can be attached to wood, pellet, coal or diesel burners.  They are worth considering if using a burner for space heating; if you have a reliable and cheap source of sustainable firewood; or if you live in a location where other energy sources are expensive, limited or intermittent.

How it Works

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 directly above the heat source. This may require longer pipe runs to hot water outlets than would otherwise be needed.

Some systems may incorporate an electric pump to increase pressure and allow transfer to storage cylinders located further away.

What to Consider

Ensure the circuit between the water jacket and the storage cylinder is open vented for safety– this means that either a low pressure open vented cylinder is required or that an isolated circuit separate from the water in the cylinder is open vented and heat is supplied to the water in the cylinder by a heat exchanger coil (this option allows the cylinder to be run at mains pressure).

Wetbacks represent an efficient auxiliary method to heat water but as a primary water heating source are inefficient. Typically a wetback connection to an enclosed wood burner has an output around 10% of the solid fuel burner output.

The burner and hot water cylinder need to be in close proximity, preferably no more than 4 m apart, if using a wetback. In addition only copper pipes should be used within a wetback system due to the high temperatures.

Use caution when coupling wetbacks with heating systems (i.e. radiators or underfloor).  Wetbacks will generally not have a sufficiently high heat capacity to supply heat to a large area thus the electric element(s) in the cylinders may end up operating more frequently than planned. 

Why it’s good

Wetbacks can be an effective option when coupled with solar hot water.  Even a well designed and appropriate sized solar system is not likely to provide sufficient hot water during the winter.  However coupling a wetback to a solar system will help provide hot water in winter and reduce use of a backup element. 

How much will it cost

Buying a burner with a wetback usually adds a few hundred dollars to the cost.

To obtain a quote for your home contact a Right House Sales Consultant.