How to use the air vents on a stove

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).

Note the primary and secondary air supplies on the front and the tertiary air supply at the back of the firebox

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.

parts of a stove, air vents
The parts of a stove, note 6, 7, 8 and 9

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!

11 thoughts on “How to use the air vents on a stove

  1. Hi, I’m burning smokeless coal in a multi fuel stove. I’m not sure if the stove has been installed correctly as with only the primary vent open I’m struggling to get past 300f on the flue pipe thermometer which is installed 1 inch above the stove.
    Is this normal for smokeless coal or does it sound as if there is a problem with the flue?

    Thanks Joe

    1. Hi Joe,
      How dry is the coal? We talk alot about burning dry wood, but the same should be said for coal, and is often overlooked. Also depending upon the stove model, the quantity of coal you are burning at any one time, might have an implication. The manual will often state the quantity of fuel required to achieve the stated outputs. If you do not know the stove type email us a picture and we should be able to help identify it. Flue thermometers are not 100% accurate, and as stoves are becoming cleaner burning, the flue gases are becoming cooler, so these thermometers are not as effective as they once were. Hope this helps. Reece

  2. I have an older stove that can burn wood or coal I’m going to burn coal I’m new at this so bare with me while i try n explain I’ve lit the coal n had it burning i have turn vents below window n vents at the bottom near ash pan I’ve only been able to get a couple hours of burn from my stove n it gets extremely hot doesn’t seem safe I have all four vents open i know I’m doing something wrong I see that I’m supposed to close top vents for coal I also have a thermostat built into stove that doesn’t seem to do anything please help

    1. Hi Tim,
      Do you know the model of the stove you have? And is it a room heater only, or does it have a back boiler in it how doing your central heating/hot water also? If your unsure email us a picture and we can try and help identify it for you. I ask this because thermostats are quite typical on boiler models, and less common on room heaters, but if it is an older stove it may of had one. Thermostats are only really useful at the start of a stove. As the dial is connected to a spring that opens and closes and air supply, but as soon as the fire is up to temperature this stays open and manually closing it will have no effect. When burning coal, you need air coming in from under the fuel bed, so the vents at the base beneath the grate where you burn will be your primary air supply. The vents above are your secondary, once the fire is up to temperature you can start to close these down, but keep it open a little, as this air is often channel down the glass and back into the fire, so assuming your stove has airwash keeping these vents open will help to maintain clean glass. So you will regulate the air supply using the bottom vents. Make sure that the ashpan is empty prior to using it, as full ashpans can both imped the air flow under the grate, but also acts as an insulator keeping the heat in under the grate which can feedback into the fire and might explain the intense heat you have been experiencing. The thermostat air supply will ensure the fire always gets some air, so you don’t need to worry about this, turn it “on” or open to start, and turn it “down” or off to when you want to shut the stove down.Couple of other things, the coals on top will often loose their colour quickly due to the exposure to the air, but the the fire will still be burning underneath. Coal should last 3-4 hours if burnt correct between refuelling periods, out of interest have you tried burning wood in the fire, i wonder if you would have a similar issue? Hope this helps, but come back to us if you need some more assistance. Reece – Fireplace Products

  3. Hi we’ve just bought and had fitted by hetas fitters a second hand Esse 200 without back boiler. The stove is about 8 years old so the vents slide sideways as opposed to the newer model that I think pulls in and out. Our problem is when we’ve got the fire burning it doesn’t seem to be heating the whole room (the room is 10 x16ft) when you stand very near to it you can feel the heat but it seems to be staying just inside the recess of the fireplace! The fitter very kindly came back to us to show us how to get a good heat going, but after about half an hour of roaring fire he agreed that it didn’t seem to be warming up as much as he had hoped! he came to the conclusion that because the chimney isn’t straight up but bends to the left( the way it was built) and we had to use a 5 inch flue because of this it didn’t seem to be drawing enough air especially with bottom vent which didn’t show any difference to the flames closed or open, he said that we probably would be better to just burn wood! Any suggestions?
    I feel miserable with my lovely fire that’s not heating the room. 😢

    1. Hi Sue, sorry to hear this we love ESSE stoves, so its odd that your experiencing this issue. Something to check is if it is a 200XK model. What this means is it has a rear vent that pulls all of its combustion air in from. They launched these around this time, so its possible you have an early XK model. If so and you have not connected the duct up it could be hampering the amount of air the stove is able to bring in and burn which correlates with what you are reporting. If you look under the stove, it will either be flat or have a manifold sloping backwards towards a round duct. If it is this model, then you either need to connect the external air feed to the stove by making a whole at the back of your fireplace and running a direct air kit to the stove. Or bring the stove further forward into the room by a few inches to allow more air into this duct. If you do not have this, as its an 8kW stove you should have a vent in the room to supply the fire with the oxygen it needs from outside, make sure this is open and not obstructed. When the fire is burning if you stand between the vent and fire your should feel the draught as the stove pulls the air in. Next make sure you are burning dry wood, this is perhaps the most common issue surrounding heat output from stoves. If your not sure buy yourself a bag of kiln dried wood and test it and see if you have the same issue. Id like to think if you had someone back that this is not the case, but worth checking. Lastly then regarding the chimney, the newer models of the ESSE 200 have a 5″ outlet on them. Unless you have a SE version of the 200 then you should have increased this to 6″, but in essence the SE version keeps the secondary air (top slider always open, so if you dont, make sure you keep this vent open). So a few things to check there, hopefully once of these will help solve your problem and you can get back to enjoying your stove once again. Best of luck, Reece

  4. Hi. We have10kw Unico double side insert stove and i just cant keep glass clean. I think i just dont know how to use air controllers correctly. Usually to start the fire i place smokeless coal then 2-3 blocks and then on the top kindling. I always leave bottom air controller open for 10-15 min then close but top air controller always stays in a middle ( looks like it should be open as well ) do i overload my stove at the start? Thanks

    1. Hi Lana, Unico that is a Lotus stove yes, and the double sided is a corner model so either the 11 or 12. So just to say we are not a Lotus dealer, so my knowledge of their products is limited but I would double check that these are multifuel stoves (i.e. can burn smokeless coal) as to the best of my knowledge the Unico like all Lotus stoves are wood only. Have you tried using the fire as a wood only stove? Do you have the same issues? We have done some videos around ways of lighting stoves, and what we find works well, so they might be worth a watch – regarding the issue at hand, if the stove is wood only then air is not coming up from under the grate which you need in order to burn smokeless coal correctly/efficiently. You may find that the coating on the inside of the glass is coming from this. I would try it with some kiln dried wood and see if you still have the issue. Thanks Reece

  5. Hi there. I am using a Hamlet wood burning stove. I light the fire with both top and bottom vents open and everything is fine. However, when I fully shut both vents, the fire is still roaring away…please could you help by explaining why this is happening…I thought with both vents shut, there should be no oxygen…thank you, Rob

    1. Hi Rob,

      So yes assuming the vents are airtight, then when you shut them down you are cutting off the oxygen supply and thus the fire should decrease. How old is the stove, checking the rope seals is a good test to make sure the stove is not “leaking” air in when the door is closed. When the stove is off open the door, rub chalk onto the door rope and close the door, open it again and you will see a chalk line on the stove body everywhere the rope touches the stove body. any gaps and that could indicate that air is leaking in. You can do a similar test with a strip of paper when the door is shut try and slide the paper between the stove body and the door. If it goes in you have a gap. As with everything you get what you pay for, and often cheaper stoves have less airtight controls and therefore have a less noticeable effect on the fire inside than more expensive models. Hope this helps, Reece

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