Ventilation is THE key factor in ensuring your wood burning stove operates correctly. Knowing how to properly use your log burner vents will allow you to create perfect ventilation for your wood burner, ensuring peak performance. So, carry on reading to find out how to properly use your log burner vents.
What are stove air vents?
Vents are a crucial part in ensuring a stove functions properly. Depending on what model stove you own, there will be one (or more) controllable air vents. The word ‘controllable’ plays an important role in that previous sentence.
Why? Because some stoves will feature both controllable and non-controllable air vents. For the purpose of this article, we are focusing on controllable air vents.
Controllable air vents are typically found underneath the stove although you may also find another controllable air vent on the top of your stove (again, this will vary depending on the model of your stove). Wood tends to burn best with a source of oxygen from above so the air vent(s) on the top of your stove will be most effective at controlling your fire.
Controllable air vents usually feature a handle so that you can easily open and close the vent.
How do stove air vents work?
To understand how air vents work, we need to first of all consider some basic chemistry.
Fire is a chemical reaction that occurs when a fuel source (wood) and oxygen in the atmosphere are ignited. Without enough fuel or oxygen a fire will be extinguished.
Therein lies the effectiveness of stove air vents. Vents allow you to control the supply of oxygen reaching the fire within your stove, and by extension, allow you to control how fiercely (or not) the fire burns.
Before we tell you more about how to use these air vents, let’s take a closer look at the air supplies within the stove.
(Pictured: Firefox 8 Twin Door Wood Burning / Multi Fuel Stove).
Air supplies in stoves
The different types of vents and openings on stoves mean that there are different types of air supplies. Understanding these will help you to understand how to operate the air vents on your stoves.
Primary air is the air which is fed to the wood located at the base of the firebox (the main cavity within the stove where the burning takes place). Primary air is used for primary combustion, to get the fire going and help the stove reach operating temperature. Primary combustion is where the fire burns the wood, creating combustible gases. However, at this stage the stove isn’t hot enough for these gases to burn. Primary combustion usually begins at around 540 degrees (282 degrees celsius) and continues up to 900 degrees.
Secondary air is the air which enters the stove through an air vent (usually located above the stove door or beneath the stove). Secondary air is used for secondary combustion. Secondary combustion occurs at around 1100 degrees onwards (593 degrees celsius) and is the stage of combustion where the gases released from primary combustion begin to burn. Secondary combustion plays an important part in your stove’s function as it’s the stage at which 60% of the total heat output of burning wood is generated.
Tertiary air is normally fed into the firebox through an opening at the back of the stove. Tertiary air is usually used to aid with secondary combustion and to reduce emissions associated with burning wood.
When you understand these various ‘types’ of air flow, and the role they play in the combustion process, you’ll see why air vents play such an important part in the proper function of a stove.
You can find out more about stove ventilation requirements in our Log Burner Ventilation Guide.
(Pictured: Tiger Inset Wood Burning / Multi Fuel DEFRA Approved Stove).
How to use stove air vents
There are no set rules for the adjustment of stove air vents. Instead you should adjust the air vents based on an approximate formula.
More air supply = increased burn + increased heat output.
Opening up the adjustable main vent(s) on your stove will increase the supply of oxygen, causing the fire to burn more, increasing the amount of heat your fire generates.
However, this will also mean that the fire in your stove burns faster and you will need to add wood to the fire more often. If your fire burns too fiercely you also risk losing the majority of the heat up your chimney. Mastering air vent adjustment is key to operating your stove at its peak efficiency.
With this information in mind, let’s go through the process of starting a fire and using the vents to control the fire once it’s burning.
Step 1 – Before adding kindling or lighting a fire in your stove, ensure that all of the controllable air vents are open. If you haven’t already got a good layer of ash at the bottom of your stove’s firebox, you should consider adding some as wood burns best with a good bed of ash laid down.
Step 2 – Light the kindling, leaving the vents fully open so there is adequate oxygen supply. Doing this will ensure that the fire will ‘take’ and start to burn effectively.
Step 3 – Once the fire has taken hold of the kindling and is burning fully, you can begin to close the controllable vents. If, as you begin to close the vents, the fire starts to smoulder and go out, re-open them. At this stage you’re very much playing a balancing act – providing just the right amount of oxygen to sustain the fire without causing it to burn uncontrollably.
Step 4 – Once the fire has spread beyond the kindling and is burning the wood, you should then adjust the vents to achieve your desired heat output. Remember, there is a trade off between heat output and efficiency. Opening the vents more will create a hot, roaring fire, but you’ll need to top up with wood more often and you’ll lose most of the heat up the chimney. Hotter isn’t necessarily better!
Tip – when the fire is taking hold of the kindling, be careful not to add too much wood, too quickly, as this can extinguish the fire.
(Pictured: Ekol Apple Pie Apple Core Ecodesign Wood Burning Stove).
Practice makes perfect
You may find that your first few attempts at lighting a fire in your stove are unsuccessful. That’s because lighting and controlling a fire in a stove is very much an art rather than a science.
As every stove is different, the amount that you should open and close your air vents will vary. But, over time you’ll learn how much you should be opening and closing the vents at each stage of the fire lighting and burning process.
Keep practicing and over time you’ll develop the techniques that’ll make starting and maintaining a fire a breeze.
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