How to operate a wood burner stove correctly
An efficient wood burner converts the highest amount of energy locked in your firewood into heat to warm the room, typically in the order of 90%. Better efficiency means less firewood needed to produce the same amount of heat and lower expense on firewood. Currently all stoves are required to be at least 60% efficient, by 2020 it must be at least 80%. This regulation only applies to new stoves and is not retrospective.
The key components of an efficient furnace are fuel, heat and oxygen. Well seasoned, dry firewood is the fuel. The heat and gases produced from burning the fuel require fire bricks (insulation) to contain it in the furnace, which then heats the room. The oxygen is supplied and controlled by the air vents.
Most stoves have either clay fire bricks or vermiculite panels. It is very important to visually inspect them for signs of wear and tear, caused from exposure to intense heat through direct contact with burning fuel. This insulator protects the outer steel/cast iron casing of the wood burner from cracking or warping. Another important item, which effects furnace efficiency, is ‘fire rope’ which is used to seal the door and glass panel. It too needs periodical replacement from wear and tear, to keep the heat in and avoid additional air flow into the stove.
Understanding How the Various Air Vents Control the Fire
Primary Air Vents are located near the base or in the door of the stove. This vent is positioned to feed air to the base of the fire bed, ideally suited for burning solid mineral fuels such as coal on a raised grate. This extra air flow underneath enable the efficient combustion of coal at a required higher temperature.
Once the log fire has started and is burning well, the Primary Air vent is normally left closed.
Secondary Air Vents (2): feed air to the top of the fire which is the most efficient for burning wood.
Air Wash Vent, usually located above the door, draws air in from the room and drags with it hot combusted gases from the fire down the inside face of the glass. This helps to keep the glass clean and clear of ash and tar.
Tertiary Air Vent (often named Cleanburn or just Secondary Air) usually operated by a slider lever at the front of the stove. It draws in room air from beneath the wood burner through a heat exchanger chamber at the back of the furnace (behind the firebricks). It is then pre-heated and drawn into the furnace at the optimum point where it combusts unburnt hydrocarbons to provide a cleaner burn, greater efficiency and improved heat output. This is only effective when the wood burner is at its operating temperature. You should visually see an improved flame.
Lighting the Fire
Open all the air vents.
If necessary remove any excessive ash from previous fires in the hearth. Leave about 25mm in to form an insulated bed which helps the wood to burn well. Many contemporary stoves now have a layer of vermiculite board for the base of the fire for exactly that reason. I have copied this idea and it helps keep the ash bed hot.
The Traditional Method is to crumple up a few sheets of newspaper and cover with dry kindling, twigs or pine cones, to form a pyramid with a firelighter at the bottom. Place a few slightly larger pieces of soft wood on the top. Light the base and close the door.
The Upside Down Method: You don’t use newspaper. Place a regular sized softwood log or two on the base. Lay some smaller pieces of wood at 90 degrees to the logs, then top with kindling, again at 90 degrees to let plenty of air flow through the pile. Place the firelighter on the top. Light and close the door.
You will immediately notice a clean burn and no smoke unlike the traditional method. This is because the heat from the firelighter flame has already started the ‘air draw’ to perform correctly in the furnace and flue to feed the fire.
Give it sufficient time for the fire to take hold before adding more wood. It generally takes about 10-15 minutes to reach a reasonable temperature.
Once the stove is burning fully at higher temperature the Primary Air Vent controls on the door should be closed and the fire controlled by the secondary ‘Air Wash’ vent alone. The Tertiary Air Vent should be set at about 50% open.
Wood burns best via air from above. You should now see a clean smokeless rolling flames in the fire box and feel a good amount of heat from the stove as it reaches working temperature. Any tar or black soot deposits on the glass from initial lighting of the fire should quickly burn off now and remain clean.
There have been significant improvements to todays wood burners compared to the older traditional models, so I recommend you refer to your stove’s manual for optimum air vent settings.
Always open the door slowly, using heat resistant gloves when the hearth is lit, or you will suck out a cloud of smoke into the room and risk spitting embers escaping. A sudden increase of air supply to the fire box is potentially hazardous.
Add more logs when older ones have burnt down to embers and small flames. Pull forward existing hot logs and add the new cold logs to the rear. You may need to temporarily open the primary air vents a little until the new fuel is up to temperature. Refuel little and often for clean, efficient burning.
Burning at the correct temperature is a critical factor for maximum heat efficiency and to minimize smoke/air pollution, tar, creosote/corrosive build up on the liner and the risk of chimney fires.
A simple and cost effective way to achieve the optimum burning temperature is with a stove top or pipe magnetic temperature gauge.
Wood burners are no different to any other type of equipment; they must be properly maintained to work efficiently.
Top of the list is sweeping the flue liner. Recommended at least before and after winter season use or more frequently for heavy use. Clean the soot build up on the baffle plate inside the stove and connecting pipes from the wood burner to the flue liner.
During the summer months always leave the air vents open (if the stove door is closed) to allow the whole system to ‘breath’. The air flow will stop condensation build up inside the wood burner and chimney liner.