FireCat Catalytic Combustors User's Guide

Purpose of this Guide

Applied Ceramic's purpose for this guide is that of giving you a better understanding on how the Firecat™ catalytic combustor works in your EPA certified catalytic stove and the role it plays in reducing harmful air pollution.

Chief information found in the guide is not a comprehensive document about the operation of any specific catalytic wood burning appliance. We suggest you consult your local fireplace dealer for the specific operating instructions as given by the stove manufacturer.
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Origin of the Woodstove Combustor

Understanding catalytic’s role in the wood burning stove industry, requires us to look back to the 1970’s when heating costs increased drastically. Oil prices increased 272% in that decade, electric rates increased 215%, while natural gas increased 483%. To combat these cost increases, many homeowners began to switch to wood as a fuel for their heating needs. This was less costly and besides firewood was free and plentiful in many areas.

Hundreds of new stove companies began to spring up. Many of them building stoves with efficiency between 50 and 70%. This was as good as or better than gas furnaces and oil burners. However, the advantages of burning wood for heating was also accompanied with some disadvantages.
  • Much wasted energy was lost in the smoke (30% in some stoves).
  • The smoke from wood-burning fires produced harmful air pollution
  • Airtight stoves burning slow produced heavy amounts of Creosote.
It was in the early 1980’s that the catalytic combustor was found to be an ideal solution aimed at answering consumer, manufacturing and environmental problems. The U.S. EPA and DEQ later set standards for the stove manufacturers to follow and a new era in wood burning began. Applied Ceramic’s role in the industry’s progress was important back then and still is today. We are the world’s largest manufacturer of catalytic combustors for wood burning stoves.

Example Cross-section of a Catalytic Woodstove


What is a Catalyst and How Do They Work?

By definition, a catalyst is not consumed or used up. The nature of a catalytic reaction is often defined as:
    "A substance, usually present in small amounts related to the reactants, that modifies and especially increases the rate of a chemical reaction without being consumed in the process."

Normally, smoke will burn, or oxidize, at a temperature of 10,000°F or higher. Burning a stove this hot would require continuous intense fire and would require a higher wood consumption. The answer to eliminate this is the catalytic combustor.

Wood smoke gases coming in contact with the catalyst causes chemical changes to take place. This will then allow the smoke to ignite at temperatures around 5000°F (or 2600°C). This temperature is easily achieved in the firebox of a wood burning stove. As the gases ignite and burn within the catalytic combustor, clean by-products of water vapor (H20) and carbon dioxide (C0²) are emitted.

What are Catalytic Combustors Made Of?

Most catalytic combustors used in manufacturing catalytic stoves today are made of a high temperature, honeycomb patterned ceramic substrate. They are coated with special noble metals like palladium and/or platinum. The honeycomb pattern gives the combustor surface area for the catalytic coatings.

How To Maintain Catalytic Burning Conditions

When Initially starting a cold stove, a medium to high firing rate must be maintained for 20 — 30 minutes. This will allow the stove, the catalytic combustor and the fuel to stabilize at a proper operating temperature, even though the temperature can reach 600°F within a few minutes after the fire has started. After the fire has started, do not turn the fire down to a low burning condition too soon. This can result in the fire and/or the catalytic combustor going out.

At the end of the burn cycle, it is possible that the amount of burning charcoal remaining may not provide sufficient temperature or fuel for the catalyst to stay lit.

During the refueling of a hot stove that has an internal temperature below 500°F, it is best to fire the stove for 10 — 15 minutes to ensure sufficient temperature and the proper amount of volatile gases for the catalyst to operate efficiently. However, when refueling a hot stove that has an internal temperature above 500°F, no re-firing is necessary.

Catalytic Combustor Temperatures

Combustor temperatures can become extremely hot during operation. Temperatures above 1600°F will damage the catalyst. Temperatures between 1400°F — 1600°F are normal, but temperatures 1200°F — 1400°F are recommended.

Why Combustors Need To Be Replaced

  • Thermal Shock
    • Occurs when refueling with wood containing moisture. Moist smoke is sent to the combustor when the by-pass is closed and the results are thermal shock and cracking of the substrate. Continual practice of this will cause the combustor to deteriorate.
  • Fatigue
    • The catalytic combustor has a six year life expectancy when used according to recommend manufacturer's guidelines. Although some combustors have operated with efficiency for as long as ten years, the combustor's life is based on the stove operator, maintenance, fuels used, and the stove manufacturer's design.
  • Mishandling
    • Dropping the combustor.
    • Using abrasive tools while cleaning it.
    • Using high pressure air to blow the cell free of debris.
    • Using cleaning solvents to clean the combustor.
    • Beating the combustor to remove it from its holding device.
  • Direct Flame Impingement
    • Flames burning for long periods of time directly into the combustor with the by-pass, or damper, closed will damage the combustor. Allowing this to happen will change the make up of the catalyst and reduce efficiency. Flame impingement will cause the substrate to break down.
  • Poisoning
    • This happens by burning materials other than seasoned, dried wood. Foreign matter such as garbage, painted wood, large amounts of colored paper, cardboard, rubber, plastic, paneling, oily products and so on, will eventually reduce the efficiency of the catalyst.

Why Combustors Might Struggle to Work Properly

  • Light-Off
    • Light-off was not achieved before the stove's by-pass was closed. This means the catalyst was not at the temperature necessary to receive and burn the inlet gases. This will result in the combustor cells plugging with fly-ash and creosote.
    • When starting a fire in a cold stove, the catalyst needs 500°F of temperature focused on it for 20 — 30 minutes to allow proper light-off.
  • Refueling Wet
    • Wet or unseasoned wood will shut the catalytic combustor down at once. This will result in the combustor's cell plugging with fly-ash and creosote. This will also cause thermal shock to the combustor's substrate and hair line cracks will occur in the cell walls.
  • Masking
    • Masking blankets the combustor with a substance that prevents catalytic activity. This can occur when burning materials other than seasoned, dry wood.
  • Plugging
    • Plugging is a build-up of soot, creosote and/or fly-ash in the combustor's cells. This occurs when the combustor is operated or positioned improperly.
    • Inlet gas temperature must be maintained around 500°F to keep the catalytic reaction active.
    • This will also occur when burning material that produce large flakes of char, I.E. wrapping paper and cardboard.

What To Do When the Combustor Is Not Working Properly

  • Check fuel supply for moisture content.
    • Fuel should be seasoned dried wood. Rain and snow are considered moisture and will produce damp smoke and steam, which are harmful to your combustor.
  • Check the flue and chimney, making sure the stove's exhaust is not blocked, nor has any obstructions.
  • Make sure the stove is getting the proper draft.
  • Check all movable parts to ensure they are working freely.
  • Make sure the combustor has not fallen out of its holding device.
  • Check the combustor for plugged cells.
  • If the combustor has been in the stove for more than six burning seasons, it might be time to replace it.
  • Be sure to follow the manufacturer's instructions for proper firing.
    • Different manufacturers, and models, require different procedures.
AS A RULE OF THUMB: The catalytic combustor requires a minimum temperature of 500°F focused on it for a period of 20 — 30 minutes to achieve light-off. This is done with the by-pass in the open position. Nothing but heat will be going to the combustor at this stage (the combustor receives the heat it requires during this time).
Troubleshooting — Problems, Causes and Solutions

Crumbling Substrate
(See Photo #1)

Extreme Thermal Shock

Refueling with Wet Wood

High Draft

Bypass combustor when the stove is running in high-fire mode.

Use seasoned, dried wood.

Do not exceed .06" of water draft. Install a manual damper and draft gauge or a barometric damper.

Fly-Ash Build-up
(See Photo #2)

Fly-Ash Masking
(See Photo #3)

Fly-ash Plugging
(See Photo #4)

Combustor has not maintained light-off temperature.

Combustor has not maintained light-off temperature.

Burning materials that produce a lot of char and fly-ash.
Closing the bypass too soon.

Brush cold combustor with a soft bristled brush or vacuum lightly.

Brush cold combustor with a soft bristled brush or vacuum lightly.

Do not burn cardboard, gift wrap or garbage.
Follow instructions for proper light-off.

Thermal Cracking
(See Photo #5)
Uneven temperatures, flame impingement and heat spikes. If cracking causes large pieces to fall out, replace combustor.
Mechanical Cracks
(See Photo #6)

Combustor mishandled or abused.

Distortion of combustor holder.

Handle combustor with care. Replace if necessary.

Replace combustor is large pieces are missing, replace any warped stove parts as well.

Plugging (Creosote)
(See Photo #7)

Burning wet, pitchy woods or burning large loads of small diameter wood with the combustor in the operating position without light-off ever occurring.
Burn dried seasoned wood. Make sure combustor has light-off before closing the bypass damper. It may be possible to burn the soot or creosote accumulation off by putting the combustor in a partially open and partially closed position after a hot fire has been started.
Masking (Soot)
(See Photo #8)

Combustor has not maintained a light-off.

Burning coal will cause a sulfur-based compound to coat the catalyst.

Place combustor in a partially open and partially closed position after a hot fire has been started to burn off the soot accumulation.

Revert to burning wood and fire the combustor to elevated temperatures for one hour.

Examples of Combustor Conditions

Click image for closeup view Click image for close-up

How To Tell If The Combustor is Working

Some stoves are equipped with a combustor view port. It should be noted that the combustor glows during the first 20 — 30% of the burn cycle, when the catalyst is receiving the most smoke and burning at a high temperature. The combustor can reach 1000°F and produce a glow. The combustor does not have to glow to be working. As less smoke is present to burn, the combustor temperature drops and the glow will cease. It is suggested that visual checking NOT be a method of determining combustor functionality.

The best method is the use of thermocouplings and following the manufacturer's instructions. This method will read the inlet and exhaust temperatures of the combustor.

Another method is to visually observe the exhaust coming from the chimney. When the bypass is in the closed position, and the catalytic combustor is in good operating condition, there should be no dark smoke coming from the chimney.

If the catalytic combustor is not working properly, the stove's operator will notice an increase in fuel usage and a build-up of creosote in the system.

How And When To Clean The Catalytic Combustor

Normally your catalytic combustor requires little or no maintenance as it generates such high temperatures, it basically cleans itself. After the first burning, the combustor should have a light gray powdery appearance.

Should the combustor's cells become masked with fly-ash, use a soft bristled brush or paint brush to dust the combustor gently.

NEVER USE ANYTHING ABRASIVE to clean the combustor. A vacuum cleaner may be used, but NEVER USE HIGH PRESSURE AIR to blow the cells of any build-up. Any cell blockage can be removed with the use of a pipe cleaner or cotton swab.

Should the combustor become masked with soot or creosote, it is possible to burn the accumulation off by opening the bypass and building a hot fire. Once the hot fire is created, close the bypass halfway and burn for 30 — 60 minutes with the bypass in this position.

Applied Ceramics strongly recommends that it would be wise to check and clean the combustor before each burning season and inspect all flues for creosote build-up. Cleaning the flue helps prevent chimney flu fires.

Helpful Hints on Firewood
Hardwoods or Softwoods?

Softwoods like Fir, Spruce and Pine are less expensive than hardwoods. Softwoods are easier to ignite and burn rapidly with a hot flame. If you want a quick-warming fire that will burn quickly, softwoods are your best choice.

However, if you are a serious wood burner using a catalytic wood burning stove, hardwoods are your best choice. Hardwoods such as Oak and Birch provide a longer lasting fire with a shorter flame.

Never burn rubbish, chemically treated wood such as discarded railroad ties, utility poles and old yard fences. All will emit poisonous fumes and could add to those materials that collect in the chimney, thus increasing the possibility of a chimney fire.

Never burn coal in your catalytic stove. Do not burn artificial or manufactured logs. These are composites of sawdust, chips, colorful chemicals, starch binders and wax. "BURN ONLY SEASONED DRIED WOOD"

How To Prepare Your Firewood

Splitting and Stacking
Splitting logs hastens drying. The key to seasoned wood is that it has been split. Splitting exposes the wet interior and increases the surface area of each piece that is to be air dried or seasoned.

Stack split wood or small round logs to allow air circulation and leave it under cover for 10 to 12 months, if possible. This will provide the best heat yield from the wood when ready to use.

Re-fueling with wood that has moisture in or on it will create a damp smoke that shuts the combustor down once the bypass has been closed.

It is not necessary to store wood in a garage as a simple covering will suffice. The idea is to keep the moisture off the wood while drying to allow proper ventilation. Store the wood away from the house as it can become a home for insects.

Selecting the Right Firewood

Heat Value
Ease of Splitting
Ease of Starting
Hardwoods (Non-Resinous Species)
Alder Medium-Low Easy Fair Moderate
Aspen Low Easy Easy Moderate
Birch Medium Moderate Easy Few
Cottonwood Low Easy Easy Moderate
Elm High Very Difficult Difficult Few
Hard Maple Very High Moderate Difficult Moderate
Mesquite Very High Very Difficult Very Difficult Few
Oak   Moderate Difficult Few
Softwoods (Resinous Species)
Cedar Med-Low Easy Easy Many
Douglas Fir Medium Easy Easy Moderate
Juniper Medium Difficult Easy Many
Pine, Lodgepole Low Easy Easy Moderate
Pine, Ponderosa Med-Low Easy Easy Moderate
Pine, White Med-Low Easy Easy Moderate
Pine, Yellow Med-High Easy Easy Moderate
Pinon Med-High Very Difficult Easy Many
Redwood Medium Easy Easy-Fair Many
Tamarack Med-High Easy-Moderate Easy-Fair Many
Willow Low Easy Fair Moderate

How To Buy Firewood

The common unit of wood measurement is the standard cord — a pile of wood stacked 8'L x 4'H x 4'W, with a total volume of 128 cubic feet. Because most people don't burn 4 ft. logs, wood is often sold by the "face cord" or rick. This is a woodpile 8'L x 4'H. The depth of the face cord could be 12", 16" or 24". (A 16" depth face is 1/3 of a full cord.)
A "truckload" is not a standard measure and depends on the size of the dealer's truck. A standard pickup holds only about 1/3 — 1/2 of a full cord. If you have purchased a cord of wood that you feel is not a full cord or not the species you ordered, contact you State Bureau of Weights and Measures.