Primary, secondary and tertiary air isdelivered into the firebox of wood burning stoves through strategically placedvents and passageways.
Some of these vents can be manuallycontrolled, while others don’t require any intervention to work.
Each form of air plays a different role inhelping to create the most amount of heat from burning wood in a stove.
So what is primary, secondary and tertiaryair in a wood burning stove, and what does each one do?
Primaryair is fed to the solid fuel located at the base of the firebox, typicallythrough the ash pan, for the purpose of helping the fire to get going and thestove to get up to operational temperature.
Secondaryair typically enters the stove through an air vent located above the door, orfrom underneath the stove, and can be used in the stove’s air wash system orfor secondary burn of gases.
Tertiaryair is fed into the firebox through the back of the stove to aid with secondarycombustion and to further reduce emissions from burning wood.
All wood burning stoves are designeddifferently. Some stoves may only have primary and secondary airflows, whileothers can have all three forms of airflow.
As every brand of stove works in differentways, I’ve explained in further detail below how primary, secondary andtertiary air works on two of our very own wood burning stoves.
To help you understand the jargon used inthis article:
Secondary burn is the process of combusting waste gases from the fire to produce more heat and reduce emissions. I’ve explained what secondary burn is in a wood burning stove in more detail here.
An air wash system in a wood stove helps to keep the glass on the door of the stove clean, and to provide a clear view of the fire. Click here to find out more.
Wood Burning StovePrimary Air Control
Primary air on a wood burning stove is themain source of oxygen for the fire as it starts and gets going.
The aim of the primary air is to get thefire up to sufficient temperature for secondary combustion of gases to occur,so that the stove can begin to provide its optimal heat output. By closing downthe primary air vent when temperature in the stove is sufficiently high, secondaryair can then take over as the main source of air for the fire.
Closing down the primary air vent helpsprevent the wood from burning too quickly, which in turn would lead to literallyburning through your supply of wood!
Primary air is fed to the solid fuellocated at the base of the stove firebox, and so primary air vents aretypically found near the bottom of the stove. Air is usually fed through the ashtray to the bed of the fire.
Primary air does not typically need to beheated prior to entering the firebox.
Wood Burning StoveSecondary Air Control
Secondary air typically takes over as themain source of oxygen to the fire once the stove is up to operating temperature.
The Environmental Protection Agency defines secondary burn as:
‘The combustion of fuel materials that are not completely burned in the primary combustion zone, i.e., in the immediate vicinity of the wood.’ Secondary combustion can be achieved by mixing the gases from the wood and from the primary combustion with suitable oxygen at a temperature sufficient to ignite the mixture or sustain burning.’
Environmental Protection Agency (EPA)
Secondary air therefore plays an importantrole in ensuring that the stove operates as efficiently as possible, and releasesthe maximum amount heat from burning wood.
Secondary air can be used within secondarycombustion of gases that are release by the fire. This releases more overallheat into your home than simply burning the wood does, and also helps to reducethe emissions from burning wood.
Properly controlling the secondary air venton your stove will ensure that you’re regulating the rate at which the wood isbeing burnt, while also ensuring that maximum heat is being generated from thestove, and that the gases are being burnt cleanly in order to reduce the totalemissions.
Secondary air vents can usually be foundabove the door of the stove or under the base. Secondary air can be heated upon the way for use in secondary burn or air wash systems as it makes its wayaround the hot body of the stove.
If both the primary and secondary air flowsare completed closed then the fire will eventually burn itself out. Thesecondary air vent should therefore typically never be closed unless you wantto put the fire out.
While leaving the secondary air vent opentoo much can prevent secondary burn from working efficiently, too little secondaryairflow can also cause the same effect.
Manufacturers should state how far open the secondary air vent should be to ensure that the wood is burning the most efficiently, and on one of our wood burning stoves it’s between a quarter and half open.
Wood Burning StoveTertiary Air Control
In some cases, tertiary air will be usedfor secondary combustion, replacing or complimenting secondary air used for thesecondary burn, which may instead be used for the air wash system.
Tertiary air typically can’t be manuallycontrolled on wood burning stoves, and so is automatically fed to the fireboxto facilitate secondary combustion (like on one our wood burning stoves shownbelow).
Tertiary air can also be heated up within apreheat chamber before entering the firebox, which aids in the ability for thestove to initiate secondary burn.
Tighter regulations on emissions fromburning wood in homes means that the wood needs to be burnt very cleanly if thestove is to be used in smoke control areas. Tertiary air helps to provide the cleanestburn possible and so can be found on a number of DEFRA or EPA approved woodburning stoves.
Wood Burning StoveAir Flow (Example 1)
My dad has a traditional looking woodburning stove located in the fireplace in his living room.
The stove has two controllable vents: onelocated underneath the stove and one located on the front.
The stove uses both primary and secondaryforms of air to feed the fire, and allows for both secondary combustion ofgases and air wash of the door to occur. There is no form of tertiary air onthis wood burning stove.
The front vent provides air to the base ofthe fire through the ash pan compartment, and up through the firebox grate.
This primary air inlet feeds air to thebase of the firebox only and so is kept wide open when starting the fire tohelp it get going. The primary vent is then either closed or left partiallyopen for the remainder of the fire.
The secondary vent controls are then used tocontrol the rate at which the fire burns. The secondary air vent on this modelof wood stove is located underneath the stove, and feeds secondary air to thetop of the firebox to facilitate both the secondary burn and air wash systems.
This secondary air vent is also left wideopen when getting the fire going, and is used to control the fire.
Again, there are no holes located on theback of this stove to provide a tertiary airflow.
Wood Burning StoveAir Flow (Example 2)
My mother’s wood burning stove is alsolocated in the living room fireplace.
The stove utilizes primary, secondary andtertiary air to operate all of the wood stoves functions.
Unlike our other stove, there is only onecontrollable vent, and is located underneath the stove.
The vent under the stove controls both theprimary air and secondary air to the firebox. Primary air is fed to the bed ofthe fire, while secondary air is directed to the top of the stove for the air washsystem.
The stove manufacturer recommends that this air vent is left open between 25% and 50% to obtain the best results when burning wood.
There’s also a vent located on the back ofthe stove to provide tertiary air for secondary burn inside the firebox (Icouldn’t reach around to take a photo unfortunately).
There are small holes located at the backof the firebox for the tertiary air to aid in secondary combustion of wastegases.
There is no manual operation required forthis vent, and tertiary air is fed automatically to the fire. The air is heatedup within the body of the stove before entering the chamber to further improvesecondary combustion.
These holes are very small, and so forcejets of hot air into the firebox to help reignite any left over gases at verytemperatures to further increase heat output and reduce emissions.
Primary, Secondary& Tertiary Air On A Wood Burning Stove
It can be easy to misunderstand how a woodburning stove delivers air to the fire for primary or secondary combustion, orto help keep the glass on the stove door clean.
Be sure to read the manual for your wood burning stove to find out which vents control which air flow, and how best to use them to have the most efficient fire in your stove.
Misusing the air controls on your wood burning stove may be causing the fire to keep going out, but ensuring to burn low moisture content wood can be just as important as using the air vents correctly.
FAQs
What is tertiary air for a stove? ›
Tertiary Air = Pre heated air comes in through air bars on the back of the stove, tertiary air is not controllable, but is there to inject more oxygen and air into the chamber to improve the efficiency as it is burning as well as providing the air for the secondary combustion, where the gases from the primary ...
What is primary and secondary on a log burner? ›Inside the wood burning stove
You should see the firebox, with air vents above and below the glass. The bottom vent is the primary vent and the top vent is the secondary vent. The vents let you adjust how quickly your fuel burns by controlling the air supply to the stove.
The secondary air vent on this model of wood stove is located underneath the stove, and feeds secondary air to the top of the firebox to facilitate both the secondary burn and air wash systems. What is this? This secondary air vent is also left wide open when getting the fire going, and is used to control the fire.
What is tertiary burn in wood stove? ›The tertiary burn system introduces additional hot air into the firebox, directly at the heart of the stove and cannot be shut down. This then ignites the unburnt gases and results in greater efficiency, a cleaner chimney and less pollution.
What are the two vents on a stove for? ›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.
How do I control the airflow in my wood stove? ›Damper vents work just like large bolts with flat heads that close over the holes when you turn the knob. If the stove only has one vent, the knob will be centered on the door; if it has two, they will be side by side. Turn the knobs clockwise to reduce the airflow, or turn it counterclockwise to increase airflow.
How do I keep my wood burner going overnight? ›You can't just throw any old wood on your fire and expect it to burn all night. The idea is to stack hard wooden logs of a regular size carefully inside the stove. If there are as few air gaps as possible, the fire will keep going for much longer than if you fill it with unevenly shaped pieces of rough wood.
What is the best way to use a wood burning stove? ›How to Operate Your Wood Stove More Efficiently - YouTube
Does wood burn from the top or bottom? ›The traditional method of fire building is bottom-up, where kindling and small logs go on the bottom to light the larger wood on top. But if you build a fire the opposite way, or top-down, it is infinitely better.
What does a secondary burn look like in a wood stove? ›After 5-10 minutes you should see blue and red flames flickering and 'dancing' horizontally at the top of the fire or the top of the glass. This is what you are looking for. It's called secondary combustion.
How can I make my Fisher wood stove more efficient? ›
Fisher Mama Bear woodstove modifications - YouTube
How much air does a wood fire need? ›An open fireplace consumes between 200 and 600 cubic feet per minute (cfm) of room air—more if it is a big fireplace with a big, big fire. Tightly built houses cannot tolerate a 200 cfm exhaust flow without getting meaningfully depressurized, so there's a problem right away.
How do secondary air tubes work? ›Secondary air tubes, located under the baffle, introduce oxygen into the hot gases released by the first phase of combustion. When temperature is hot enough, this causes a second combustion above the wood that burns almost all the fine particles and gases before they are evacuated through the chimney.
Where is air inlet of stove? ›Most stoves have a primary and a secondary air inlet control. The primary air inlet is situated near the ash pan and the secondary air inlet near the top of the wood burning stove. Those are the two inlets you need to regulate manually during combustion.
How do you vent a wood burning stove? ›For instance, wood-burning stoves will always be vented through the roof of your house, but pellet-burning stoves can be vented vertically through the roof, or horizontally through the wall to the outdoors. Same with gas stoves - venting can be routed in either direction - vertically or horizontally.
Can you put too much wood in a wood stove? ›For normal use do not place more than 2 pieces of wood in the oven at one time. If you want a heavier effect you can put more wood into the stove. When you put new wood in the stove you have to open for the primary air at the bottom of the door until the fire is burning well.
When should I close the damper on my wood stove? ›A fireplace damper should always be kept open while the fire is burning. Furthermore, keep the damper open until all the embers are completely out; since smoke and dangerous carbon monoxide can enter the house. Once the ember bed is entirely out, close the damper.
Should I close damper wood stove? ›You don't want to leave your wood stove damper fully open, though, because then the heated air will continue to escape, and your room won't get warm. By closing the damper, it will reduce the oxygen levels in the chimney, and you'll have a longer fire. According to Northeastern Chimney, this also creates a downdraft.
Why can I smell smoke from my wood burner? ›Soot smell from woodburner
As with a smoke smell, a smell of soot from your woodburner could indicate a need to have your chimney swept. It might also suggest that the wood you're burning is not sufficiently seasoned and has a high moisture content. The soot smell is indicative of a creosote build-up in your chimney.
A damper is usually located approximately 12 to 18 inches from the stove, prior to the spot where the pipe exits into a chimney, if present. The damper retains heat that escapes up the chimney or flue. It allows this heat to dissipate into the area being heated by the woodstove.
How do you make logs burn slower? ›
Add your kindling and tinder on top of the pile, and then light your fire from the top. Once the top of the pile is caught, shut off the primary air control entirely, and feather in your secondary air control to slow your burn rate.
Can I leave the flue open overnight? ›The smoke from burning wood contains carbon monoxide, so in order to prevent this toxic byproduct from entering your home, it is important to leave the flue open overnight. This enables a draft to carry the compound out into the atmosphere, instead of sinking down the chimney and saturating the room.
How long should a log last on a wood burner? ›Generally, tests show that heat logs will burn for around 2 - 3 hours. Now, that's not a very specific answer to the question 'How long do fire logs last? ' but there are so many factors that will affect burn time, as well as the composition of the log.
What should you not burn in a wood stove? ›- Cardboard in all forms (including pizza, cereal, and shipping boxes) should never be burned in your fireplace. ...
- Magazines & Wrapping Paper. ...
- Dryer Lint. ...
- Fire Accelerant & Lighter Fluid. ...
- Incorrect Types of Wood.
To get the most heat from your wood burning stove, the temperature should be between 260 and 460°C. Any lower than this, your fire will be burning too slow to generate a good amount of heat. Don't think that you can make your fuel last longer by burning it slowly, either.
How do I get the most heat out of my log burner? ›Control the Air Flows
This plays an important part in how to maximise heat from a log burner. You'll need to keep the primary air vent open to get the fire going. Once the fire is burning nicely, you can slowly close the primary air vent and use the secondary air vent to control the air flow.
What is an Upside Down Fire? An “Upside Down Fire” is a simple technique that burns from the top to the bottom using less wood with a longer burn time. The pieces of wood are arranged by stacking back and forth in opposite directions. Add tinder and kindling on top and light to allow the flame to catch the lower half.
Why does wood burn better on a bed of ash? ›Wood burns better on a layer of ash because the ash helps to insulate the warmth and also helps to reflect the heat back onto further pieces of wood. It can also take a while for firebox surrounds to heat up from cold, and so a bed of ash can help to get the fire going more quickly.
What is the best way to stack logs in a fireplace? ›Take two of the biggest logs and place them parallel with the back of the fireplace on top of the grate. Leave space between them for the flames to reach up over the logs. Take some of the smaller logs and place them perpendicular on top of the bigger logs. Place the kindling on top of the smaller logs in a loose pile.
How long does a wood stove take to heat up? ›Quick answer: A wood stove takes an hour to heat your home by 5-10F. It takes approximately 3-6 hours depending on the house and insulation to reach the final temperature. If your wood stove is your primary heat source, you should kindle the fire at least 3 hours before you need a comfortable temperature.
What is the difference between catalytic and non catalytic wood stoves? ›
A catalytic stove is designed to burn off even more of the smoke and ash before venting to the outside. A non-catalytic stove does not use a catalytic combustor to ignite the smoke and produce more heat. It does have a few design elements that ensure it will, however, burn as efficiently as possible.
What is double burning? ›Burned at a high temperature. This does not mean two firings.
What is the cleanest burning wood stove? ›The Cape Cod™ is Lopi's "Super Stove" boasting 80% efficiency (HHV, using B415 test) and 0.45 grams per hour, making it the cleanest burning wood stove as tested on the U.S. market. This stove features a massive firebox and convection heat exchanger and is designed to be durable and attractive in cast iron.
Are newer wood stoves more efficient? ›Wood heaters manufactured before 1990 burn wood less efficiently, which wastes fuel, pollutes outdoor air and creates dust in your home. Replacing an old wood heater or fireplace with a more energy efficient EPA-certified appliance can save fuel, money, and protect you and your family's health.
Can I add a catalytic converter to my wood stove? ›The basic concept can be applied to just about any roughly cubic metal (steel or iron) wood burner. Since the converter must reach a temperature of at least 500°F before it “lights off,” a location close to the fire will insure that the unit starts working as soon as possible and continues to do so throughout the burn.
How much wood do I need to heat my house for winter? ›“The standard rule of thumb is that a 1,000-square-foot home will use three cords of wood for a season,” she says. “If your wood burning stove is super high-efficiency, or if you live in a more moderate climate, you may need less.”
Do I need an air vent with a wood burning stove? ›To operate correctly all stoves require a supply of air for combustion, and the ability to then evacuate the flue gases; otherwise they will not work. A wood burner is unable to light without an air supply, and subsequently smoke will then pour out into the room it is installed, not what you want to happen.
How much firewood do I need per day? ›In general, you'll find that you need between 2 and 5 bundles of firewood per day for your campfire. However, you may need more wood if you plan to have a fire going for more than just a few hours each night.
What is the purpose of tertiary air? ›Tertiary air is fed into the firebox through the back of the stove to aid with secondary combustion and to further reduce emissions from burning wood.
What is secondary air on a wood stove? ›Secondary burn or combustion on a wood stove is the process of burning off waste gases higher up in the stove in order to produce more heat and to reduce emissions. A second feed of air over the fire in a wood stove firebox helps secondary burn to occur.
What are secondary air tubes wood stove? ›
Air intake tubes are what bring oxygen into a wood stove to fuel the combustion of a fire. Secondary air tubes are completely different. They work off of the combustion from inside the stove. Once a wood stove gets hot enough, secondary air tubes take over and help reburn particulates inside of the stove.
What is tertiary air for a stove? ›Tertiary Air = Pre heated air comes in through air bars on the back of the stove, tertiary air is not controllable, but is there to inject more oxygen and air into the chamber to improve the efficiency as it is burning as well as providing the air for the secondary combustion, where the gases from the primary ...
How does a wood stove draw air? ›How the air supply system works on your wood burning stove - YouTube
What does the top vent do on a wood burner? ›The vents let you adjust how quickly your fuel burns by controlling the air supply to the stove. On the top of the stove you'll see a pipe coming out of the wood burner. This is the flue, which is a duct that carries away all the waste gases and smoke and directs it to be released outside via the chimney.
Is it better to vent wood stove through wall or ceiling? ›You can use single wall pipe up to the ceiling, but you must use insulated pipe through the ceiling, attic and roof. 2. Wood stove pipe can be installed horizontally through the wall or vertically through the ceiling. You should try to keep your pipe as straight as possible, so the vertical method is recommended.
What is the 2 10 rule? ›A chimney must project at least 3 feet above the roof on its shortest side and also be at least 2 feet above any roof structure that is within a 10 foot radius of the chimney. That's it. Following this simple rule helps to ensure other structures on the roof do not interfere with the exhaustion of combustion gases.
How do you adjust the airflow on a wood stove? ›Damper vents work just like large bolts with flat heads that close over the holes when you turn the knob. If the stove only has one vent, the knob will be centered on the door; if it has two, they will be side by side. Turn the knobs clockwise to reduce the airflow, or turn it counterclockwise to increase airflow.
How do you vent a wood burning stove? ›For instance, wood-burning stoves will always be vented through the roof of your house, but pellet-burning stoves can be vented vertically through the roof, or horizontally through the wall to the outdoors. Same with gas stoves - venting can be routed in either direction - vertically or horizontally.
How do you use a multi fuel stove vent? ›Leave the air vents on your stove open immediately after the fire has been lit to provide plenty of air flow into the firebox. This helps the fuel to catch. When your fire has reached the desired level, close the primary air vent to halfway.
How much air does a wood fire need? ›An open fireplace consumes between 200 and 600 cubic feet per minute (cfm) of room air—more if it is a big fireplace with a big, big fire. Tightly built houses cannot tolerate a 200 cfm exhaust flow without getting meaningfully depressurized, so there's a problem right away.
How do secondary air tubes work? ›
Secondary air tubes, located under the baffle, introduce oxygen into the hot gases released by the first phase of combustion. When temperature is hot enough, this causes a second combustion above the wood that burns almost all the fine particles and gases before they are evacuated through the chimney.
Is it better to vent wood stove through wall or ceiling? ›You can use single wall pipe up to the ceiling, but you must use insulated pipe through the ceiling, attic and roof. 2. Wood stove pipe can be installed horizontally through the wall or vertically through the ceiling. You should try to keep your pipe as straight as possible, so the vertical method is recommended.
What is the 2 10 rule? ›A chimney must project at least 3 feet above the roof on its shortest side and also be at least 2 feet above any roof structure that is within a 10 foot radius of the chimney. That's it. Following this simple rule helps to ensure other structures on the roof do not interfere with the exhaustion of combustion gases.
Can you put too much wood in a wood stove? ›For normal use do not place more than 2 pieces of wood in the oven at one time. If you want a heavier effect you can put more wood into the stove. When you put new wood in the stove you have to open for the primary air at the bottom of the door until the fire is burning well.
When should I close the damper on my wood stove? ›A fireplace damper should always be kept open while the fire is burning. Furthermore, keep the damper open until all the embers are completely out; since smoke and dangerous carbon monoxide can enter the house. Once the ember bed is entirely out, close the damper.
How do I keep my wood burner going overnight? ›You can't just throw any old wood on your fire and expect it to burn all night. The idea is to stack hard wooden logs of a regular size carefully inside the stove. If there are as few air gaps as possible, the fire will keep going for much longer than if you fill it with unevenly shaped pieces of rough wood.
How long does a cord of wood last in a wood stove? ›A full cord of firewood can last as little as 5 or 6 weeks or as much as 10 or 12 weeks. If wood is the sole fuel-type you're using to heat your house in the wintertime (no gas or electric heaters helping reduce wood usage), you can expect a full cord of wood to last no more than six weeks.
How many logs burn an hour? ›If you have a wood-burning fireplace, you will need more logs to get a good fire going. The general consensus is that six to eight logs will provide enough heat for an hour or two. You may need more or less depending on the size of your fireplace and the type of wood you are using. What is this?
How much wood do I need to heat my house for winter? ›“The standard rule of thumb is that a 1,000-square-foot home will use three cords of wood for a season,” she says. “If your wood burning stove is super high-efficiency, or if you live in a more moderate climate, you may need less.”
How can I make my Fisher wood stove more efficient? ›Fisher Mama Bear woodstove modifications - YouTube
How does secondary combustion work in a wood stove? ›
The secondary burn takes place near the top of the Solo Stove's burn chamber. The upper vent holes along the inside of the fire pit or camp stove blasts the fire with preheated oxygen, creating a hotter and more beautiful fire while burning off smoke. All this happens due to our Signature 360° Airflow Design™.
What is the difference between catalytic and non catalytic wood stoves? ›A catalytic stove is designed to burn off even more of the smoke and ash before venting to the outside. A non-catalytic stove does not use a catalytic combustor to ignite the smoke and produce more heat. It does have a few design elements that ensure it will, however, burn as efficiently as possible.