There are three really important issues which determine the efficient operation of your multi fuel stove or wood burner. Understanding these 'three basics' will go a long way in helping you to operate your stove efficiently and also help you to identify any potential problems.
- Understanding the importance of an effective flue system
- Understanding the importance of good dry wood fuel
- Understanding the function of the stove's controls
An effective flue system
Firstly you must ensure your installation is efficient – that is, you must have a good flue system with sufficient up-draught. Our friends at Dan Skan stoves always say that the flue system is the 'engine' of the stove and that without it performing well it doesn't matter how much money you've spent on the stove and how good your fuel is, the stove will always disappoint you. This is the main reason that we recommend using a Hetas Registered Installer to fit the stove and why you should fit a flexible flue liner. When you fit a flue liner at the same time as you fit your stove the installer is fitting a complete heating system, limiting the potential for 'engine' failure. The flue liner provides a smooth and consistent draw throughout its length and when insulated with vermiculite it limits the potential for cold spots within the system which cool the flue gases and reduce the effectiveness of the up-draught. The flue terminal also needs to be considered and there are a variety of cowls which should only be specified by your installer to compensate for particular operating conditions such as prevailing wind or poor flue draught.
We can usually guarantee quite a number of phone calls when we get the first serious cold snap from people complaining about their normally operational stove suddenly not 'drawing' and smoke consequently coming into their room. During very cold periods most flues require a 'kick-start' to get the up-draught working so it is critical that you understand the significance of a good pre-fire. The colder it is then the bigger your pre-fire should be to get that vital 'blast' of hot air which will quickly warm the flue system and create the necessary up-draught.
Good dry wood fuel
Wood burning stoves are not like open fires – you just can't burn anything on them. Even if you could – you shouldn't! The days of burning materials which cause nuisance smoke or unnecessarily pollutes the air that we breath are, we're pleased to say, long gone. Wood burning stoves require wood logs with a moisture content of less than 20% to work efficiently. At The Stove Yard, most problems that we see with stoves can usually be attributed to a poor flue system (see above) or wet or unseasoned logs being used (particularly noticeable with boiler stoves). Wet or unseasoned wood logs provide little or no heat, are hard to keep alight, reduce the effectiveness of the air wash system so the stove glass goes black and, within a matter of weeks, could quickly clog up your flue system. In contrast, using well-seasoned logs provides plenty of heat and allows you to control the flame pattern for the best fuel efficiency. These higher temperatures also avoid the creation of creosote and excessive soot deposits which reduce the efficiency of the flue system. In addition when the stove is operating at the correct temperature it is also at its most efficient allowing the air wash system to work properly to keep the glass clean.
The stove's controls
Always read the manufacturer's instructions. To repeat – wood burning stoves are not like open fires, you have to understand how you can get the best out of them. They are much, much, more controllable than an open fire and the way that you control the supply of combustion air to your stove determines how well your stove will work for you. You must also understand that the two main fuel types require different types of air. Primary Air, for burning mineral fuels (smokeless ovals etc) and Secondary Air for burning wood and wood products.
Primary air, required for burning mineral fuels, is the air that arrives at the fuel load from underneath the fire grate and is usually controlled by the large circular knob at the bottom of the stove door (eg Morsoø Squirrel 1412 or Baby Gabriel) or alternatively a slide control (eg Dunsley Highlander 5 or Esse 100). Secondary Air, required for burning wood, is the air that arrives from above the fuel load and not from underneath, and is usually controlled with a slide control above the top of the door (eg Stovax Stockton 5 or Charnwood Country 4). Both these types of air are essential for the efficient burning of the different fuel types. At different stages of the burn cycle, depending on your stove, flue draught and and fuel type, you may need to experiment and use a mixture of both. However, always remember that turning down the secondary air supply when burning wood logs could also limit the effectiveness of the stove's airwash system.
Then there's pre-heated Tertiary Air. This is air which is introduced high up inside the fire chamber and delivers extra combustion air just as the flue gases are about to leave through the stove's flueway, thus providing any remaining particulates a final chance to ignite, making the stove cleaner burning and wringing out a few additional efficiency percentage points along the way. Tertiary Air is controlled in conjunction with the Secondary Air and does not have its own control function. Stoves from Dan Skan and Charnwood ranges incorporate some clever mechanisms to ensure that the correct levels of Primary, Secondary and Tertiary Air can easily be delivered with just one user-friendly control.
Finally, there really isn't any substitute for reading and re-reading the instruction manual. Part of the CE test and Hetas approval involves the suitability of the instructions, so generally speaking they should provide you with all of the information that you need to get the best from your stove.