How Does a Wood Burning Fireplace Insert Work?

Wood burning fireplace inserts have become an increasingly popular way to add warmth and ambiance to homes. But how exactly does a fireplace insert work? In this comprehensive guide, we’ll walk through everything you need to know about wood burning inserts, from how they function to installation, maintenance, and safety tips.

What is a Wood Burning Fireplace Insert?

A wood burning insert is an appliance that is installed into an existing masonry fireplace. The insert consists of a firebox surrounded by a decorative facade, essentially converting the fireplace into a wood stove.

Unlike a traditional open fireplace, inserts are sealed installations with tight-fitting doors. This allows them to burn wood much more efficiently and effectively than conventional fireplaces.

There are two main types of wood inserts:

  • Non-catalytic wood inserts – These have a traditional firebox design with secondary combustion. They do not have a catalytic combustor.
  • Catalytic wood inserts – These inserts have a catalytic combustor, which allows more complete combustion, less smoke, and higher efficiency.

In both styles, the fire burns in the firebox inside the insert. The insert facade is designed to cover up the masonry fireplace opening for a clean, finished look.

How Does a Fireplace Insert Work?

Fireplace inserts work by containing the fire in a sealed firebox with an insulated steel exterior. Here is an overview of how they function:

  • Air intake – Inserts draw in air for combustion through an air intake. There is a primary air intake at the bottom front of the insert and a secondary air intake at the top.
  • Firebox – The firebox is surrounded by insulation and contains the fire. It has an interior baffle to direct airflow.
  • Convection channels – Room air circulates through convection channels around the firebox to be heated before exiting vents at the top to warm the room.
  • Flue – Exhaust gases exit through the flue collar at the top of the insert into the existing chimney. This draws smoke up and out of the home.
  • Glass door – A large glass viewing door provides a view of the fire while sealing in combustion.
  • External shell – A steel or cast iron shell surrounds the firebox and contains the convection channels.
  • Blower – Most inserts include a blower that pushes air through the convection channels for increased airflow and efficiency.

This sealed, insulated construction allows the insert to reach high temperatures for efficient wood combustion. The insert radiates heat into the living space both directly from the hot fire and from the warmed convection air.

How Does Combustion Work in a Fireplace Insert?

There are a few key aspects of combustion that allow modern EPA certified fireplace inserts to burn wood cleanly and efficiently:

Primary and Secondary Air

Air for combustion enters through two separate intake channels:

  • Primary air enters below the door and supplies oxygen for the main fire. It can be controlled via an air control lever.
  • Secondary air enters above the firebox at the top. It provides oxygen for secondary combustion of unburned smoke and gases, reducing emissions.

Firebox Design

The firebox has an insulated steel interior and a heat-reflective baffle plate. This helps ignite gases released from the wood while retaining heat.

Convection Channels

Room air flows through convection channels around the firebox to be warmed before exiting through top vents. This air circulation improves heat transfer to the room.

Catalytic Combustor (Some Models)

Catalytic inserts have a combustor coated in a catalyst that allows combustion of smoke and gases at lower temperatures, increasing efficiency.

This combination allows for a cleaner, highly-efficient wood fire.

What Are the Benefits of a Fireplace Insert?

There are many good reasons to consider upgrading a masonry fireplace with a fireplace insert:

Increased Efficiency

Fireplace inserts burn wood much more efficiently than open fireplaces, delivering 10x as much usable heat to the home.

Lower Emissions

The combustion design of an insert reduces smoke output significantly for cleaner indoor and outdoor air quality.

Controlled Burn

The tightly sealed firebox with precise air controls allows you to regulate the fire’s intensity, temperature, and burn time.

Zone Heating

An insert’s radiant and convection heat focuses warmth in the main living space you use most.

Fire Safety

Inserts are designed to contain sparks and embers, reducing the fire hazard of burning wood indoors.

Consistent Heat

Inserts provide steady, even heating over a long burn period, unlike a fireplace’s fluctuating heat.


The flickering flames and warmth create a beautiful hearth atmosphere.

When chosen and operated correctly, a fireplace insert can be an effective way to increase energy efficiency and enjoyment in your home.

What Are the Parts of a Fireplace Insert?

Fireplace inserts consist of several components that work together for combustion and heat circulation:

Firebox – The metal (usually steel or cast iron) enclosure that contains the fire. It has an insulated interior and heat-reflective baffle.

Door – A tight-sealing glass door allows view of fire while sealing in smoke. Airwash system keeps glass clean.

External shell – Surrounds firebox and forms convection channels and air passages. Made of steel or cast iron.

Air intakes – Primary and secondary air intakes provide oxygen for combustion.

Flue collar – Connects to chimney flue thimble for exhaust exit.

Surround panel – Decorative panel that covers fireplace opening.

Convection channels – Passages that circulate room air around firebox to transfer heat.

Blower – Fan to force air through convection channels for increased airflow.

Log retainers – Holds firewood in place.

Rheostat – Allows speed control of blower.

Catalytic combustor – Secondary combustion unit containing a catalyst (in catalytic models only).

Air control – Adjustable lever that regulates primary air intake.

How to Install a Fireplace Insert

Proper installation is crucial for fire safety and maximum efficiency. Insert installation is complex and should always be done by a certified professional. But here is an overview of the general install process:

Fireplace Inspection

The existing masonry fireplace and chimney must be thoroughly inspected before installation. The chimney must meet requirements for structural integrity, height, and interior dimensions.


The insert must be properly sized for the fireplace dimensions. Measure the fireplace opening carefully and choose an insert that fits the space.


In most jurisdictions, permits are required for insert installations. The installer will obtain the necessary permits.

Prep Work

The masonry hearth may need minor modifications to accommodate the insert. A chimney sweep should be done if needed.

Insert Positioning

The insert gets positioned securely inside the fireplace and attached to the floor. Leveling bolts are used to ensure it is flat and stable.

Flue Liner

A stainless steel flex liner gets routed from the insert up through the chimney. This upgrades the flue for safety.

Surround Panels

Decorative surround panels are installed around the front of the insert to cover up the fireplace opening.

Connection to Chimney

A section of rigid pipe connects the flue collar to the chimney thimble. This seals off the chimney space.

Final Adjustments

The insert gets bolted into its final position. The façade and trim are completed to integrate it aesthetically.

Testing and Curing

Initial curing fires are small, low-heat burns that season the components. The draft is tested to confirm proper venting.

With cautious attention to clearance requirements and venting codes, an experienced technician can install your insert safely and effectively.

How to Use a Wood Burning Fireplace Insert

Using your fireplace insert properly is important for efficiency and safety. Follow these tips for best results:

Select Good Firewood

Choose seasoned hardwoods like oak, maple and ash that have been split and dried for 6-12 months. Softwoods and green wood smolder inefficiently.

Start Small

Begin with a small kindling fire and gradually add larger logs once it is established.

Adjust Air Intake

Control the primary air intake lever to regulate heat output, burn time and reload frequency.

Maintain Temperatures

Keep temperatures in the ideal range (between 500-600°F) for clean combustion in the firebox.

Let the Coals Rekindle

Allow leftover coals to rekindle before adding more logs for continuous combustion.

Inspect the Chimney

Check the chimney and flue regularly for any creosote buildup or debris.

Be Attentive

Stay nearby during operation and refuel as needed to maintain the fire.

Extinguish Properly

Allow the fire to burn down completely or use a dry chemical extinguisher for safety.

Following the manual’s guidance will help you get excellent performance and many years of enjoyment from your fireplace insert.

Troubleshooting Common Fireplace Insert Problems

Like any complex appliance, wood inserts can encounter occasional issues. These troubleshooting tips cover some of the most frequent problems:

Smoking Out the Front

  • Check that all seals are tight and the door is properly closed.
  • The flue may be blocked or the draft is weak. Have the chimney inspected.
  • Reduce the primary air intake to slow the burn rate if it is too high.

Glass Door Gets Dirty

  • Burn hotter, cleaner fires around 500-600°F.
  • Make sure you are using dry, seasoned wood.
  • Check the door gasket for any leakage points.

Burns Too Fast

  • The air intake may be too far open, creating excess airflow.
  • Use larger log pieces so the fire burns slower.
  • Check the door and damper seals for leaks.

Not Producing Enough Heat

  • Increase air intake to raise fire intensity.
  • Check blower operation to ensure proper airflow through convection channels.
  • Clean catalytic combustor if present.

Smoke Smell in House

  • Increase chimney draft by inspecting the flue or adding chimney height.
  • Always open the flue before lighting.
  • Check for backdrafting or leaks.

Creosote Buildup

  • Burn hotter fires around 500°F to reduce deposits.
  • Only burn dry seasoned wood.
  • Have chimney cleaned annually.

Getting an insert properly installed and maintaining it carefully will prevent many issues. But following these tips can help troubleshoot any problems that do arise.

Fireplace Insert Maintenance

Regular maintenance will keep your wood insert running safely and efficiently for years. Follow these tips:

Annual Professional Cleaning – Have the insert and chimney cleaned and inspected yearly by a certified technician.

Gaskets – Visually check gaskets and replace any that are broken, corroded or no longer sealing properly.

Door Glass – Clean glass regularly with a fireplace glass cleaner.

Catalytic Combustor – If catalytic, inspect and clean the combustor per the manufacturer’s instructions.

Chimney Inspection – Check the chimney and flue for any buildup or obstructions.

Surfaces – Vacuum ashes and dust from the insert decoratively. Clean surfaces as needed.

Fire Brick – Replace any cracked or crumbling fire brick inside the firebox.

Blower – Clean out blower air passages regularly to remove dust and debris.

Paint – Touch up paint on metal surfaces as needed to prevent rust and corrosion.

Door Latch – Lubricate the door latch periodically to keep it opening and closing smoothly.

Firewood – Ensure firewood stock is kept dry and seasoned.

Flue – Have the chimney re-lined if the flue shows corrosion or deterioration.

Following the insert manufacturer’s maintenance guidelines is always recommended. With proper care, your fireplace insert can provide cozy warmth and visual appeal for decades.

Fireplace Insert Safety Tips

While wonderful for ambiance, wood inserts do require some safety precautions:

  • Have the insert and chimney professionally installed to ensure proper clearances.
  • Always use a metal mesh screen in front of the insert to prevent sparks escaping.
  • Keep furnishings, curtains, and other combustibles at least 36 inches away.
  • Install smoke and carbon monoxide detectors near the fireplace.
  • Let ashes fully cool in a metal can for safe disposal later.
  • Keep a fire extinguisher handy.
  • Keep children and pets away during operation.
  • Crack doors or windows initially to test draft.
  • Only burn dry, seasoned hardwoods.
  • Have the chimney cleaned annually.
  • Keep the doors closed whenever the insert is not in use.
  • Always open the flue before lighting a fire.
  • Never leave a fire unattended.
  • Extinguish the fire completely before going to sleep.

Respecting proper precautions will allow you to enjoy cozy fires safely.

Frequently Asked Questions

Q: How much work is required to install an insert?

A: Installation is generally a big project that requires modifications to the hearth, new flue liner, and electrical work. Hire a certified professional.

Q: How much heat can an insert provide?

A: A properly-sized modern insert can heat 500 – 2000 square feet effectively through radiant and convection heating.

Q: Can I install an insert myself?

A: Insert installation is complex and must meet codes. It is not a DIY project. Have a certified technician do it.

Q: Does an insert require special maintenance?

A: Annual professional cleaning of the insert and chimney are crucial. You’ll also need to inspect components and gaskets periodically.

Q: What temperature range should the fire burn?

A: For cleanest combustion, aim to keep the firebox between 500-600°F. An insert thermometer helps monitor this.

Q: How long does an insert last?

A: With proper installation, maintenance, and use, a high-quality insert can provide 30 years of reliable service.


Wood burning fireplace inserts allow you to convert an inefficient masonry fireplace into a beautiful source of heat for the home. Following guidelines for installation, operation, and maintenance will keep your insert performing properly for decades. With some care and safety awareness, a fireplace insert can be an excellent heating upgrade that also enhances your living space ambiance.

Laura Kassovic

Laura Kassovic, a former engineer at Intel SOC, now dedicates her efforts to mentoring startups in the realms of Wearables and AI. As a co-founder of New Tech Brake, she spearheads a wireless sensing solution enterprise catering to diverse applications including product development, research, location tracking, and people monitoring, as well as asset and cargo supervision. The platform empowers developers to craft an array of innovations such as fitness trackers, temperature-monitored cargo systems, medical trial tools, smart running garments, or even straightforward transmission of unprocessed accelerometer data to cloud-based repositories.

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