What is slumbering your stove? When your appliance is set on low or minimum output, for overnight burning to be revived in the morning without the need for relighting is called “Slumber Mode”.
Some mineral fuel burning appliances are designed to operate in slumbering mode and should be tested to show that they are safe to operate in this manner.
Beware When Slumbering your Stove
New users should be aware that there are problems associated with using an appliance for extended periods at a low output, especially if the appliance is not designed to operate in this manner.
These problems will occur when the appliance has not been sized according to the heating load applied to it so that it must be turned down to low output for the living space to be comfortable.
Problems with Slumbering a Stove
When running your appliance at a low output, that can lead to incomplete combustion, especially when burning a high volatile content fuel such as wood logs. This can lead to the formation of sooty and dry deposits on the flue lining as well as increased levels of carbon monoxide and particulates in the products of combustion.
When appliances are used at a low output for extended periods of time, the temperature of the chimney reduces and there is a tendency for the products of combustion to also be lower in temperature – which will lead to an increased likelihood of condensation forming in the chimney.
Condensation together with flue deposits that may contain acidic compounds will present a risk of corrosion where metallic components are used for the flue lining. If you intend on using the appliance for slumbering on a regular basis then it is wise, whenever it is necessary to reline the chimney, to choose a lining system that does not have metallic components.
Regardless of the appliance being designed for slumbering, it is still necessary to adapt to certain practices to reduce the negative effects of operating at low outputs. This involves running the appliance at high output following slumbering to hopefully burn away flue deposits and ensure the chimney warms up sufficiently to provide a good draught and reduce the risk of condensation. You should never overload an appliance.
Flexible Liners and Slumbering
While being easier to install and replace, flexible liners are not designed to last the life of the building but may last more than 10 years. When slumbering your wood burning stove for a long period and/or infrequent chimney sweeping can cause corrosion damage which has been known to reduce the expected life of a flexible metal flue liner to less than five years.
The life expectancy of any chimney is dependent upon correct use and maintenance. Pre-cast and Masonry chimney products, while usually offering long life and high resistance to risk of corrosion, tend to involve more installation work when compared with metallic chimney systems.
Metal liners and insulated metal chimneys offer fast and convenient installation. They can be less resistant to damage by corrosion, particularly if subjected to abuse or inadequate cleaning. This allows soot or condensate deposits to accumulate in metal lined chimneys and prolonged periods of burning in slumbering conditions, particularly on closed appliances, can cause high concentrations of corrosive condensates to build up and attack the metal liner. This situation can not only considerably reduce the life of the flue lining but can also invalidate the manufacturers’ warranty.
Carbon Monoxide, Particulates and Slumbering
It’s important not to allow the appliance to repeatedly remain in slumber mode for long; this practice ultimately starves the appliance of air giving rise to increase of carbon monoxide and particulates. Owners of a wood burning stove is not always aware of the dangers of doing this, if they don’t want to put another log on the stove at the end of the evening, they often open the doors to extract the last bit of heat from the stove.
The heat-recovery design of the stove normally causes the products of combustion to take a tortuous route around the stove to the flue, but when the stove cools there is not enough energy to drive products in this way.
The embers are still producing quantities of carbon monoxide, have insufficient heat energy to drive the products to the flue in the normal way, so the products take the easier route and spill into the room through the open door.
Appliance Output
It is imperative that the output of the appliance is considered when planning any stove installation; should the appliance be oversized then this may give rise to the end user operating the appliance with the controls turned down, effectively slumbering the stove. An appliance with an output too small for the room it is being used in will lead to inadequate heat output.