What is an Airwash System?

We cannot think of any current model stove, certainly none that The Stove Yard sell, which does not feature an Airwash System to help keep the glass clean. Some manufacturers have given their Airwash Systems their own fancy names – but don't be confused, they are all essentially the same thing with the Secondary Air and the Airwash being one and the same 'system'. When you control the Secondary Air, either with its own control or part of a single control combustion air management system, you are effectively controlling the Airwash.

How the Airwash works

The Airwash function is generally delivered by Secondary Air (top air) diverted down along the front of the glass by means of a baffle (not to be confused with the baffle plate). You can clearly see this at the top of the entrance to most fire chambers. Air is heated (hence why the term 'pre-heated' is sometimes applied) as it is drawn inside the fire chamber to feed the fire and as it does this it is sent across the top of the Airwash baffle and drawn down along the front of the hot glass to 'wash' away any dry particulates which have settled there during the the burn cycle. On most stoves the airwash is only delivered from the top, but for example on Hwam premium wood burners, their tall windows are also air washed from the sides.

Why the Airwash sometimes won't work the way it should

What an airwash system won't do however, is remove any sticky tars from the glass which are derived from burning unseasoned wood (wood with a moisture content of more than 20%) or prohibited fuels such as plastics. Wet wood introduces moisture into the fire chamber, consequently dropping the fire chamber temperature, which in turn further reduces the effectiveness of the airwash system. Long periods of slumber burning, with flue gas temperatures of less than 120ºC, will also affect the airwash system's performance and produce unburned particulates and tarry condensates which will stick to the glass.

As a wood fuel load is burned away then the heat output is naturally reduced and again this limits how well the Airwash System will perform. This is most noticeable (but not always) when you return to the stove the next day when some stoves can show signs of minor sooting at the bottom of the glass as the fire has died down. This is perfectly normal and if the wood you have used is properly seasoned then you should be able to easily remove this soot with some kitchen roll or newspaper without the need for a proprietary stove glass cleaner. 

Failing door rope seals can affect the Airwash

As a stove door rope seal begins to fail this can allow the stove to draw some uncontrolled combustion air into the fire where any leak in the seal occurs. As this air will be naturally cooler than the air and combustion gases inside the firechamber then this can sometimes reduce the effectiveness of the Airwash. Always check your door firerope regularly and replace with the correct diameter fire rope – too large may damage the hinges and too small may be ineffective. A replacement rope seal will not only improve the Airwash but could also save you money by preventing uncontrolled combustion of your fuel because it is probably burning faster at times than it needs to.

Multi fuel stoves and the Airwash

Most multi fuel stove manufacturers recommend only using approved smokeless mineral fuels when not burning wood in their multi fuel stoves and therefore the Secondary Air / Airwash System should not necessarily be needed to keep the glass clear. These smokeless fuels are naturally cleaner burning and, because they are not wood, they do not therefore require a supply of Secondary Air from the top (so no Airwash either). Instead, for best combustion and effective control, smokeless coal should take its air supply from beneath the grate (known as Primary Air). This is why there is an open grate on multi fuel stoves and often a separate control for Primary Air.