Wood burning stoves have been used for centuries to provide heat and cooking fuel. Modern wood stoves have evolved into highly efficient heating systems that burn wood or pellets with reduced emissions. Understanding how they work helps ensure proper operation and maintenance.
What is a Wood Burning Stove?
A wood burning stove is an enclosed metal or stone structure designed to efficiently burn wood as a primary heat source. The stove contains the fire in a firebox chamber surrounded by metal or masonry. Outside air is brought in through air vents to fuel the fire, providing heat through radiant and convective heat transfer.
Stoves may sit directly on the floor, or have legs to raise them up. They come in various sizes, shapes, and styles. Basic operation is similar despite differences in aesthetics and features. Stoves may have large single doors, or be made of steel or cast iron with small doors for loading fuel and removing ashes.
Key Components of a Wood Burning Stove
Several main components work together to make a wood stove function properly:
The firebox is the main chamber that contains the fire. It should only be large enough to hold enough wood for one burn cycle, typically 30 minutes to 1 hour. Oversized fireboxes result in inefficient slow burns and excess emissions. The firebox walls absorb heat and radiate it into the room.
Air inlets or air vents control the amount of air entering the firebox to support combustion. There is a primary air inlet at the base allowing air into the bottom of the fire, and secondary air inlets above the fire introducing air to burn the gases released from the wood. More air results in a hotter fire, while less air produces a slower fire.
Baffles are plates inside the top of the firebox that trap heat and gases to improve combustion efficiency before venting up the chimney. They help transfer heat and also protect the stove top from direct flames.
The flue is the interior channel that directs smoke and exhaust from the firebox up through the chimney. It should be the same size as the stove exhaust outlet for proper draft.
Some stoves have a catalytic combustor, which is a ceramic honeycomb coated with catalysts that further burn smoke and particles before exiting up the chimney. This reduces emissions and extracts more heat from the exhaust.
How Does a Wood Stove Work?
Wood stoves work by efficiently controlling air flow and combustion to transfer heat from a contained fire into the room. Understanding the stages of burning wood helps explain how stoves produce heat.
Primary combustion begins when wood is initially lit. The wood slowly burns releasing flammable gases which ignite from the nearby flames. As wood chars, it allows more gases to escape. Too much air can cool the fire, while too little prevents full gas combustion. Once the gases are burning, the fire intensifies and heat radiates outwards.
As wood chars and the fire becomes established, secondary combustion occurs when the released gases mix with air, igniting above the fuel. Air entering through the secondary inlets supports this top-down burn of the gases. Burning the gases generates additional heat and reduces emissions.
The primary heat transfer methods in a wood stove are:
- Radiant heat – Heat directly radiates from the fire and stove walls. The metal or masonry absorbs heat and emits infrared radiation into the room.
- Convective heat – Heated gases rise and circulate through the room, transferring heat through convection. Internal chambers and external heat shields can enhance convective heat flows.
- Conductive heat – Some heat conducts through the stove surfaces directly contacting the floor. Adding legs raises the stove reducing conductive losses.
- Catalytic heat – Exhaust gases pass over the catalytic combustor releasing additional heat that is radiated or convected into the room before exiting the chimney.
Controlling the airflow into the stove regulates burn rates and heat output. Adjusting the primary air vents manages the amount of air entering the base of the firebox. This controls the intensity and heat of primary combustion.
Secondary air inlets are typically fixed, but may have adjustable openings to regulate secondary combustion of the gases above the fire. Some stoves have a thermostat controlled damper that automatically adjusts air intake to maintain desired heat levels.
Emissions and Efficiency
Modern wood stoves burn more cleanly and efficiently than old models. Steps are taken to generate maximum heat while minimizing harmful emissions:
- High temperatures foster more complete combustion, reducing emissions.
- Secondary combustion burns remaining gases, reducing smoke particles and emissions.
- Baffles and catalytic combustors further decrease emissions and particle pollution.
- Insulated fireboxes reach higher temperatures using less fuel.
- Air control systems optimize the fuel-to-air ratio for a more efficient burn.
When operated properly, the latest wood stoves reduce particle emissions by over 90% compared to older stove designs.
Wood Stove Operation and Maintenance
Operating a wood stove safely and efficiently requires following proper procedures for lighting, fueling, and cleaning.
Lighting a Fire
Follow these steps when starting a fire in a wood stove:
- Open the air inlets fully to establish a hot fire quickly.
- Place several crumpled newspaper balls in the center of the firebox.
- Arrange small kindling pieces in a teepee shape over the newspaper.
- Add a few small split logs on top of the kindling.
- Light the newspaper and close the doors, allowing air vents to remain fully open.
- Once the kindling and logs have caught fire, larger split logs may be added.
When refueling an already lit stove:
- Adjust air controls to allow the fire to settle before opening the door.
- Use fireplace gloves when adding logs to prevent burns.
- Place logs carefully on top of established coals, stacking loosely to allow airflow.
- Re-close door and readjust air controls to desired burn rate.
Cleaning and Ash Removal
Regular cleaning improves efficiency and prevents hazards:
- Ashes should be removed before they reach the secondary air inlets, usually every few days depending on use.
- Chimneys and flues should be cleaned annually or as needed based on creosote buildup from condensed smoke.
- Stove glass may be cleaned as needed using commercial stove glass cleaners.
- Catalytic combustors must be replaced approximately every 5-7 years when they lose efficiency.
Proper maintenance ensures a wood stove continues burning safely and efficiently for years to come.
Types of Wood Stoves
There are many wood stove varieties designed for different aesthetics and heating needs:
Cast Iron Stoves
Cast iron stoves retain and radiate heat well with a classic appearance. They heat evenly once warmed up but respond slowly to air control changes.
Steel stoves heat up and cool down quickly, but retain less heat than cast iron. Their thin walls allow inexpensive designs.
Soapstone is quarried and shaped into smooth stove surfaces. It has excellent heat retention to provide gentle, even warmth.
Ceramic stoves retain heat moderately well. Their smooth tiles are easily cleaned but can crack if handled roughly.
Pellet stoves burn compressed wood pellets that are automatically fed into the firebox. Pellet stoves provide even heating with minimal user effort.
Wood Stove Safety
Wood stoves present certain safety considerations:
- Fire hazards – Stoves and flues reaching over 400°F can ignite nearby combustibles. Proper clearances are crucial.
- Smoke – Old stoves emit more smoke particles inside and out, posing health risks. New EPA certified stoves dramatically reduce particle pollution.
- Carbon monoxide – Improper drafts or blocked chimneys can lead to dangerous CO buildup inside the home. CO detectors should be installed nearby.
- Creosote fires -Burning unseasoned wood creates creosote buildup in chimneys and flues that can ignite into extremely hot fires. Regular cleaning reduces creosote accumulation.
- Burns – Stove surfaces exceed 300°F when hot and can cause serious burns. Fireplace gloves should always be worn when operating the stove doors, vents, and controls.
Following manufacturer guidelines, installing proper venting, using seasoned wood, and regular cleaning and maintenance ensure wood stoves provide safe and reliable heat for years to come. With the right precautions, you can enjoy cozy radiant warmth from a classic wood-burning stove.
Frequently Asked Questions
What types of wood are best to burn in a stove?
Hardwoods like oak, maple, and ash that have been split, stacked, and air-dried for at least 6 months contain less than 20% moisture and provide the most heat and easiest ignition. Softwoods and green wood are difficult to burn and lead to more creosote buildup.
How do I know if my chimney needs cleaning?
Chimneys should be inspected annually for creosote buildup. More than 1/8 inch accumulation requires cleaning to reduce chimney fire risks. Flue inspections can determine when professional chimney cleaning is needed.
Why is my stove burning slowly and producing excess smoke?
This is likely caused by weak draft from an overloaded firebox, closed vents, or insufficient chimney height and heat. Try opening the air vents fully and using smaller loads of wood until the fire is burning briskly before adjusting the air controls.
Can I install a wood stove myself?
Stove and flue installation involves significant expertise. Using non-combustible surfaces, proper floor protection, minimum clearance distances, and expert electrical, venting and permitting knowledge are essential to safety. Professional installation is highly recommended.
How often should I have my chimney cleaned?
Industry recommendations are once per year or after every 4-5 cords of wood burned, whichever comes first. More frequent cleaning may be needed if burning less-ideal wood or seeing increased creosote accumulation. Talk to a chimney sweep about an appropriate cleaning schedule.