What are the parts of a wood burner stove called?

A wood burning stove can be as much as 80% more efficient than an open fire, which means you get a load more heat indoors than you’d get from an ordinary fire. It’s also a lot safer and cleaner than open flames.  So how does the stove do its magic, what are the various parts called, and what do they do? Let’s take a look at the guts of a wood burner. 

Why is a wood burner so much better than an open fire?

Wood burners are usually made from cast iron. Cast iron conducts heat beautifully, which means it gets extremely hot really quickly. The iron body then radiates the heat outwards like a massive chunky radiator, warming the space much more efficiently and cheaply than an open fire, which outputs some heat out into the room but sends most of it up the chimney. That’s where the ‘80% more efficient’ number comes from.

While they all look different, and there are some funky contemporary designs around, the bits and bobs all work in much the same way. The main parts are the firebox, air vents and their controls, the baffle, flue collar and the flue itself, stove pipe, doors, ash pan, damper, and last but not least, if you have them on your model, a catalytic combustor or even an autopilot system.  

The firebox

The firebox is simply the main compartment inside the stove, the place you put the fuel and the bit with the single or double glass doors on the front. The firebox is lined at the back and both sides with special masonry fire bricks or lined with some sort of cement or metal. Some stoves, the multi-fuel versions, will have a metal grate at the bottom on which you build your fire. If it only burns wood there’ll be a fire resistant base of some sort.

Why the difference? Coal burns differently from wood, needing an air source from below to light and burn properly, but wood doesn’t.

As a rule the bigger your stove the bigger the fire box, the larger the fire and the more heat it chucks out. But whatever the stove size, when you use dry wood with the correct low moisture level the stove works more efficiently, converting more of the energy held in the wood into heat. This keeps the waste gases in the firebox inside for long enough so you get something called ‘secondary combustion’.

The air vents and their controls

Every stove model has at least one set of air vents, potentially more than one. Some have multiple sets. These deliver oxygen to the fire from various places around the fire box. There are three sorts of air: primary, secondary and tertiary.

Primary air is sent to the base of the box where the fire sits, important for getting things going nicely and heating things up initially. Once the fire’s merrily burning away the primary air flow isn’t so important, so you can shut those vents.

Once the fire’s doing its thing the secondary air vents take over, and if you have them the tertiary vents come into their own as the main oxygen source. Because the secondary air comes in either from below or above the stove, you’ll usually find the secondary vent under the stove or at the front at the top. This air delivers oxygen for the secondary burn, and also helps to keep the glass clean on the inside so you can see the fire, something called the air wash system.

Tertiary air replaces the secondary air as your main source of oxygen for the secondary burn, and you’ll usually find the vents for this at the back of the stove. You can’t control these manually. They just do their thing, always open while the primary and secondary vents are almost always manual – unless you have a stove with an autopilot system.  More about those later.

Using the primary and secondary air vents, you can control how fast and well the wood burns. It’s best to keep the primary vent open when you start the fire and rotate the vent to control the airflow to the base of the fire to maximise the oxygen supply. Then you can completely or mostly close it to let the secondary vent take over, using the little slider and handle to control it. Leave this secondary vent open when you first start the fire too, then once the fire’s roaring you can use it to fine-tune your burn and control the air wash system.

The baffle

The baffle is simply a metal plate at the top of the firebox. Its job is to keep fire by-products inside the firebox for as long as possible. Because such a high proportion of the heat generated comes from the secondary combustion of waste gases, keeping them in the box for longer means they burn off better and don’t end up being wasted, just sent up the chimney.   

The baffle handles very high temperatures well but only when you don’t exceed the maximum heat for the model you’ve chosen. Any hotter and you can damage it.  

The flue collar

Basically the stove pipe is connected to the stove via the flue collar, joining the stove to the flue. You’ll find the flue collar near the top of the fireplace, usually behind the baffle and above the firebox. The flue collar itself marks the join where the stove meets the pipe that goes up the chimney or out of the room in another way.

Depending on the stove model you might find the collar on top of the stove or the back, to suit the direction the flue leaves the house. It can go vertically through the ceiling, out at an angle through an external wall, or out via a chimney. Many wood burning stoves are installed inside old chimneys with the stove pipe going vertically up the flue inside the chimney.

The stove doors

The door or doors usually have glass in them so you can see the fire. They have a fireproof rope-like seal around the edges to keep the heat and gases inside and make sure as much air as possible gets through the vents into the firebox. When these eventually come loose or degrade you can buy replacement sealing rope and use special heat resistant glue to fix it in place.

The ash pan

Multi fuel stoves tend to have ash pans, wood-only stoves usually don’t. You’ll find yours just under the firebox, there to catch and collect ash as it falls through the grate.

The grate

If you have a grate you can use the lever to the side of the stove on the outside to rotate it, which sends ash down onto the ash tray for easy cleaning and emptying. You might want to hoover out the ash after a few burns to keep everything clean and allow the maximum air flow.

If there’s no ash tray because your stove only burns wood, you’ll need to remove the ash manually, or use a hoover to get it all out of your firebox.

Things you might or might not have – The damper

You might or might not have a damper. Some old models have a damper inside the stove pipe that you can open or shut to control the ‘draw’, AKA the air flow. Used with the air vents it helps control the burn rate of the fuel and the heat emitted. New stoves don’t tend to have dampers.

Things you might or might not have – The catalytic combustor

Some of the newest high efficiency wood stoves have a catalytic combustor to deal with pollution, lowering the temperature gases burn to give you a cleaner, lower-emission burn.

Things you might or might not have – The autopilot system

As mentioned in another post some stoves have a special autopilot system, notably Hwam, the Danish firm that invented the system. When the stove is cold the primary air flow automatically opens to deliver as much oxygen as possible. Once the fire is burning and the temperature begins rising a metal coil starts to expand, moving a small lever that shuts down the primary air flow and opens up another to switch you into main burn mode. Then the system cleverly continually changes the primary, secondary and tertiary air without you having to do it yourself.

Experiment with all these stove controls and you’ll soon find the most fuel- efficient way to stay as warm as possible for the smallest spend on fuel.