A key difference between a stove and an open fire is the capability to control the amount of oxygen fueling the fire thanks to the air vents.
Oxygen is a very important player when it comes to fire, but too much of it can cause the fire to burn through the fuel very quickly and you risk over firing the stove.
But before we can talk about air control, it is important that you understand how the air vents work (and familiarise yourself with the parts of a stove).
You may be familiar with the terms ‘air wash’, primary, secondary and even tertiary air supply, if you already own a stove. Air wash means that air is drawn over the glass window inside the stove, keeping the glass relatively clean.
Due to the slightly cooler temperature of the window, ash and tar is more drawn to this surface and is likely to stick to it. With a constant flow of air from the air-wash system, it is less likely this build-up of tar will occur (but there will be some build up inevitably). This comes from the secondary air supply, typically found above the ceramic glass window.
Primary air comes from the bottom of the firebox and is particularly used when burning coal.
If you are burning wood, you need to keep the firebox temperature very high, helping wood release its flammable gases. To keep supplying the fire with oxygen but not cooling the temperature inside the firebox with cold air, the secondary air supply often preheats the air before it reaches the firebox by bringing the cool air through channels close to the firebox, warming it before it exits into the firebox.
Many stoves have a tertiary air supply which helps to burn off the gases released by the fuel. These are usually found at the back of the firebox and can be seen creating a swirling vortex of fire. This improves efficiency and makes for a cleaner burn.
Now that you know how your stove receives air we can talk about controlling it.
When you come to light your stove you should have all air controls open. This will give your fledgling fire its best chance of taking hold, and some people keep the door ajar during the early lighting process.
It is also worth checking your ash pan isn’t too full and that ash isn’t restricting air supply.
Once the fire has taken hold you can close the bottom (primary) air supply off completely if you are burning wood, as a wood fire predominantly takes oxygen from above the fire. When burning coal, control the fire with the primary air vents as coal fires predominantly take oxygen from below the fire.
It is important to adjust the air vents to ensure that the fire is burning hot enough for a clean burn, with all fuel being burnt off, but not so hot that it burns the fuel too quickly and damages the stove.
Like most things, it is worth practising and seeing what works best for you and your stove. There are often so many factors, from how air tight your room is to the direction of prevailing winds, that affect your stove that we couldn’t list everything you should do, so the more you use it the better you become at understanding what it needs and the steps you need to take to keep it working at its best.
Whilst this blog post serves as a quick crash-course in the workings of a stove’s air supply, we’re in the process of producing a series of videos that go into depth about various stove’s air supplies and how each one works, so keep checking back for those!
In the meantime if you have any questions about your stove please do not hesitate to comment below and we’ll endeavour to help you rectify the problem!