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A Hearth and Heating Glossary

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Glossary of Common Hearth and Heating Terms - Our thanks to Quadrafire, Majestic, Temco and others who contributed to this list.

Please submit new words to [email protected] or ask for permission to edit this page.

ABSORPTION—Amount of water a masonry unit will absorb when completely submerged in either cold or boiling water for a set length of time. Absorption amount is expressed as a percentage weight increase.

ABSORPTION RATE—Weight of water absorbed by masonry unit (usually brick) in one minute.

ACCELERATOR—Material added to mortar to speed up setting time.

ACTIVE SOLAR HEATING—Indirect solar heating; solar heat is circulated mechanically (by pump or fan) from solar collectors outside the building.

ADD-ON—Solid fuel furnace or boiler that shares a heat distribution system and links controls with the existing conventional fuel appliance.

ADJUSTMENT SCREW—Part of pressure regulator used to regulate gas pressure. It should only be set with a manometer or pressure gauge.

AFUE - annual fuel utilization efficiency The AFUE rating is a measure of how much of each dollar’s (or units) worth of fuel burned by your appliance goes toward heating your home. Electric heat (radiant) is nearly 100% efficient since there is no chimney loss. Stoves, however, do put some heat and some unburnt fuel up the chimney. This is all figured into the AFUE.

AIR CONTROL—See Air Inlet Control.

AIR INFILTRATION—Typically, the passing of air into the house through small cracks or gaps inherent to the structure. Affected by temperature difference between the inside and outside of the structure, and air pressure factors (e.g. wind, the operation of solid fuel appliances or electrical appliances such as fans).

AIR INLET—The designed port(s) of entry for combustion air in a controlled combustion, solid fuel burning appliance.

AIR INLET CONTROL—The means by which the amount of air entering the air inlet is regulated. Also referred to as air control.

AIR SUPPLY—Broadly, the air that is supplied to the firebox of the solid fuel burning appliance.

AIR-TO-FUEL-RATIO—The ratio of air and fuel, by weight, in a solid fuel appliance. It should be noted that 1 pound of dry air occupies a volume of 13.315 cubic feet at 70 degrees F. Therefore, 35 pounds of air, the typical amount of air necessary to burn 1 pound of wood in a fireplace, occupies 466 cubic feet.

AIRTIGHT STOVE—A stove in which a large fire can be suffocated by shutting the air inlets, resulting ultimately in a large mass of unburned fuel remaining in the stove.

AIRWASH—A built-in system in many new stoves that keeps the door glass clean.

ALDEHYDES—Class of compounds with distinct pungent odor, produced during incomplete combustion of a fuel gas.

ANCHOR BOLT—Threaded bolt placed in grouted masonry unit opening (or in concrete wall top) used to fasten wood sill, beam, or other structural support to wall top.


ANGLE IRON—A structural iron angle shaped like an L used for lintels to support masonry over openings, such as doors or windows.

ANSI—American National Standards Institute. The coordinating organization for federal national standards system, consisting of 900 companies and 200 trade, technical, professional, labor, and consumer organizations.

ANTHRACITE COAL—Hard coal, with high carbon and low volatile matter (gas and vapor) content.

APPLIANCE—A solid fuel burning stove, fireplace, furnace, boiler, water heater, or cookstove.

APPLIANCE REGULATOR—The appliance component, usually part of the combination valve, that maintains constant gas pressure.

APPLIANCE TO FLUE—Means of venting a solid fuel appliance (including fireplace inserts) into masonry fireplace chimneys; the stainless steel connector passes from the appliance to the first fire clay flue liner. Also referred to as direct connection.

APPROVED—Acceptable to the authority having jurisdiction

ARCH—Curved structural support across the top of an opening.

ASH—Noncombustible solid by product of solid fuel combustion.

ASH DRAWER—Receptacle beneath the combustion chamber that catches and contains ashes until removal.

ASH TRAP—Compartment or receptacle behind the combustion chamber that catches and contains fly ash removal

AUGER—Screw-like or worm gear like device that delivers Pellets from the hopper (or from a cup device) through a tube to the burn pot.

AUGER MOTOR—Electric motor that turns the auger.

AUTHORITY HAVING JURISDICTION—The organization, office, or individual responsible for approving equipment, installation, or procedure.

B VENT GAS—Listed, factory-built, double wall metal pipe for venting appliances with draft hoods and other appliances listed for use with Type B Gas Vent.

baffle—An obstructing device or partition in a solid fuel appliance, used to direct air add heat.

BAFFLE PLATE—A partition inside an appliance to control the flow of direction of combustion air, flames, or flue gases.

BAROMETRIC DRAFT CONTROL/REGULATOR—A device designed to prevent excessive draft in a fuel burning appliance by automatically admitting the appropriate amount of air to the venting system. Draft regulators are usually installed in chimney connectors.

BAROMETRIC DRAFT REGULATOR—Control device installed in chimney connectors to prevent excessive draft. The installer or appliance operator sets the regulator for the desired draft, after which the regulator automatically admit room air into the venting system to maintain desired draft.

BEARING WALL—Wall that supports part of the building weight above it in addition to its own weight. Opposed to a non bearing wall.


BIO-MASS—Renewable organic source of fuel

BITUMINOUS COAL—Soft coal with up to a 40% volatile matter content and consequently lower carbon content.

BOILER, HOT WATER—Central Heating appliance for heating water and circulating steam or hot water to the house through pipes.

BOILER, STEAM—A steam central heating appliance

BOTTOM FEED—Pellet appliance fuel feed design which delivers pellets from beneath or behind the burn pot. Also known as underfeed and includes side feed.

BREACHING—Horizontal access into a chimney for a chimney connector. In prefabricated chimneys, a T provides a breaching. In masonry chimneys, breaching are holes that should have sleeves or liners of tile or heavy steel.

BTU OR BRITISH THERMAL UNIT—A unit for measuring energy, equal to the amount of energy needed to increase the temperature of 1 pound of water by 1 degree Fahrenheit.

BURN BACK—The condition of smoke or of charred, smoldering, or burning pellets in the hopper

BURN POT—Metal or ceramic device in the combustion chamber where fuel and air are mixed and primary combustion occurs.

BURN RATE—Combustion rate, usually expressed in pounds of fuel consumed per hour.

BUTANE—A colorless, odorless, non toxic gas; not generally used in hearth appliances.

BY-PASS Damper—Term specifically referring to the movable plate in catalytic wood burning appliances which in one position channels the flue gases through the catalytic combustor. On some non-catalytic appliances, a moveable plate that redirects and increases residence time of gases.

CALORIFIC—Energy Value

CANNING SYSTEM—Device surrounding catalytic combustor, usually consisting of insulation mat and stainless steel can or holder.


CARBON DIOXIDE—CO2. Colorless, odorless noncombustible gas produced by the complete combustion of carbonaceous fuel; is non-toxic.

CARBON DIOXIDE—A gaseous product of combustion

Carbon monoxide—CO. Colorless, odorless, combustible, and toxic gas produced by the incomplete combustion of carbonaceous fuel, resulting in the combining of 1 rather than 2 oxygen atoms with 1 carbon atoms.

CARBON MONOXIDE—A toxic, combustible gas formed in incomplete combustion.

CARCINOGENIC—Cancer causing.

CAST IRON STOVE—A material used in many stoves. Iron is heated to a liquid form and poured into molds, usually with decorative details.

CATALYST—A substance which increases the rate of a chemical reaction without being consumed in the process. In solid fuel use, usually the precious metals palladium and platinum. Applied to the wash coat of the catalytic combustor.

CATALYTIC COMBUSTOR—Device designed to increase combustion efficiency by lowering flue gas ignition temperatures. Consists of substrate, wash coat, catalysts and canning system.

CHASE—A structure built around, and enclosing portions of chimney exterior to the house.

CHIMNEY—A portion of the venting system, through which flue gases are vented to the outdoors and by which penetrated combustible surfaces are protected; a primarily vertical shaft enclosing at least one flue, the design of which results in a natural draft.

CHIMNEY BREACHING—A means of venting a solid fuel appliance into masonry fireplace chimneys; the chimney connector passes through the chimney wall to the inside of the flue liner by means of a thimble or approved pass-through device.


CHIMNEY CAPACITY—The maximum safe venting capability of a chimney, most often expressed in terms of the fuel consumption rate of connected appliances (in btu per hour), but more fundamentally related to the mass flow (e.g. pounds per minute) of flue gas which will flow up the chimney under given conditions of temperature and barometric pressure.

CHIMNEY CONNECTOR—The portion of the venting system between the appliance and the chimney. Commonly called stovepipe. Stovepipe is commonly used for chimney connectors. Some appliances have no connectors because the chimney connects directly to the appliance. (e.g., many prefabricated fireplaces).

CHIMNEY FIRE—The burning of soot/creosote deposits inside a chimney or stovepipe.

CHIMNEY LINER—Usually a high temperature clay round or rectangular sleeve lining the interior of masonry chimneys. Although not recognized by many building codes, other materials such as stainless steel stovepipe and enameled porcelain coated steel industrial chimneys can be used as liners.

CHLORIDE—A form of salt tested for in Pellet Fuel Institute (PFI) pellet fuel standards.

CIRCULATING FIREPLACE—A fireplace with multiple-wall construction around the fire chamber which permits air to circulate between the walls, become heated, and enter the house directly or via short ducts.

CIRCULATING STOVE—Also see circulating fireplace. A stove with an outer jacked (usually sheet metal) beyond the main structure, with openings at or near the bottom and top so that air can circulate between the stove body and its jacket. For purposes of determining safe clearances, a circulating stove must be fully jacketed on all four sides, including at the access doors and on the top.

CLEAN-OUT—Opening at base of fireplace for cleaning out ashes.

CLEAN-OUT DOOR—Means for closing and sealing the opening provided for inspection and removal of creosote and other chimney deposits; should be well sealed against air infiltration.

CLEARANCES—Minimum distance, composed only of an air space, which must be maintained between a heat source such as an appliance or vent and combustible surfaces.

CLINKER—Lava-like cluster of fused ash and silica that an block combustion air inlets in the burn pot.

CLINKER BRICK—A very hard burned brick whose shape is distorted or bloated due to nearly complete vitrification.

COLD JUNCTION—Non-heated end of the thermo-couple/thermopile.

COMBINATION VALVE—Gas valve which combines control functions; usually consists of gas manual valve assembly; pilot safety shutoff system, diaphragm valve, gas pressure regulator, and valve operator.

COMBUSTIBLE MATERIAL—Material made of or surfaced with wood, compressed paper, plant fibers, or other material that will ignite and burn, as applied to materials adjacent to or in contact with heat-producing appliances, chimney connectors, steam and hot water pipes and warm air ducts. Such material shall be considered as combustible even though flame proofed, fire retardant treated, or plastered.

COMBUSTIBLES—(as applied to walls, floors and ceilings in the context of wood heater clearances for safety). Constructed of or surfaced with wood, paper, natural- or synthetic fiber cloth, plastic or other material which will ignite and burn, whether flame proofed or not and whether plastered or unplastered. Combustibility is a relative concept. This definition is adapted from the definition in NFPA booklet glossary of terms relating to heat-producing appliances.

COMBUSTION—The process of burning, or oxidation accompanied by heat. When sufficiently rapid, also accompanied by light.

COMBUSTION AIR FAN—Electric motor and impellers which supply air to support combustion of the fuel in the burn pot. May be located ahead (upstream) of the burn pot and deliver the air under positive pressure, or after (downstream of ) the burn pot and deliver the air under negative pressure. Usually provides force to remove byproducts of combustion through the venting system, but may only provide combustion air.

COMBUSTION CHAMBER—Area where mixing of combustion air and fuel occurs. Includes burn pot, refractory panels, and a door with glass.

COMBUSTION EFFICIENCY—The percentage of the total energy content of the fuel consumed that is converted to heat in the fire.

COMBUSTION RATIO—Required amount of air that must mix with 1 cubic foot of gas to have complete combustion.

COMPRESSION STATION—Place where pressure of natural gas is increased before it continues farther along the pipeline.

CONDUCTION—Direct transfer of heat from one material to another.

CONTROL BOARD—Integrated, solid state circuit that controls and synchronizes fuel, combustion air, and convection air delivery.

CONTROL PANEL—Contains switches, dials, indicator lights, and possibly adjustment screws for operating the appliance.

CONTROLLED COMBUSTION—Complete burning of fuel with a steady flame when fuel and air supplied at proper rate. Contrast with explosion.

CONTROLLED COMBUSTION APPLIANCES—Solid fuel appliances with relatively tight seals. The amount of air entering the air inlet, thus the combustion rate in the firebox, is operator controlled.

CONVECTION—The transmission of heat by the circulation of a fluid (air or water) caused by differences in temperature (and therefore density).

COOKSTOVE—A wood or coal burning appliance with a closed fire chamber, which is intended primarily for cooking and includes an oven.
COPING—Masonry cap on top of a wall or pier; wall top covering.

CORROSION—The natural process of metal decay. It is hastened by repeated heating and cooling.

CREOSOTE—Chimney and stove pipe deposits originating as condensed wood smoke (including vapors, tar and soot). Creosote is often initially liquid, but may dry or pyrolyze to a flaky or solid form. Smoldering wood (or coal) is the main source of creosote.

DAMPER—A valve, usually a moveable or rotatable plate, for controlling the flow of air or smoke and draft.

DECORATIVE GAS APPLIANCE IN A VENTED FIREPLACE—A self-contained, freestanding fuel gas burning appliance designed for installation only in a vented fireplace and whose primary function lies in the aesthetic effects of the flame. Gas hearth appliances which are listed to ANSI Standard Z21.60 include gas log sets.

DEW POINT—The temperature at which liquid water forms from vapor.

DIAPHRAGM—Part of pressure regulator which responds to changes in gas pressure to maintain constant outgoing pressure.

DIETHANOLAMINE TREATMENT—Chemical process of removing hydrogen sulfide and carbon dioxide from gas. Sweetening the gas.

DIRECT SPARK IGNITION—A type of intermittent ignition system that ignites the gas directly at the main burner by means of a spark.

DIRECT VENT—Method of venting appliance whereby all air for combustion is derived directly from the outside atmosphere and all flue gases are discharged directly to the outside atmosphere.

DIRECT VENT—Exhaust system for gas fireplaces that can be power or gravity induced. No full height chimney is required.

DIRECTIONAL HOOD—A part of the pilot burner that directs the flame against a control device and then out across the main burner.

DISTILLATION—Separation of solids and liquids from gases by application of heat. Method of extracting LPG from wet natural gas.

DOMESTIC WATER—The water piped through a house to basin, sink, shower and tub outlets. It is presumed potable, as contrasted with industrial water.

DOWNDRAFT SAFETY SWITCH—A feature on gas stoves designed to automatically shut off the stove if there is a downdraft in the chimney.

DRAFT—The difference in air pressure at the same elevation between the inside and the outside of a chimney, chimney connector, or appliance. The term draft is also sometimes used to denote the rate of combustion air flow into a fuel-burning appliance, or the rate of flue gas flow.

DRAFT HOOD—A device built into an appliance or made a part of the flue or vent connector from the appliance designed to (1) provide for the ready escape of flue gases in the event of no draft, back draft, or stoppage beyond the draft hood; (2) prevent a back draft from entering the appliance; and (3) neutralize the effect of stack action of the chimney or gas vent upon the operation of the appliance. Also known as draft diverter.

DRIP—In gas piping, a tee device used to collect condensate from gases. Installed so that they can be serviced to remove condensate. Also known as drip leg.

EFFICIENCY—The percentage of heat that goes into the room instead of up the chimney. 70-80% efficiency is optimal.

ELBOW (CHIMNEY CONNECTOR)—The portion of the chimney connector that turns or bends, up to 90 degrees per elbow. Some types of elbows are adjustable from 90 degrees to 0 degrees (no bend).

ELECTRONIC SNIFFER—A device which emits a loud, piercing noise in the presence of very small amounts of certain gases. Used in gas supply line and appliance leak detection.

EMISSIONS—Unburned gases and smoke left after combustion.

ENAMEL—A permanent baked on heat-resistant, glossy, colored finish used on the outside of a cast iron stove.

ENERGY EFFICIENCY—The percentage of the total energy content of the fuel consumed that becomes useful heat in the house.

EPA PHASE I AND II—Environmental Protection Agency particulate emissions standards for solid-fuel stoves, designed to reduce pollution. Implemented in 1988 (phase I) and 1990 (Phase II).

EPA REGULATIONS—Government regulation of woodburning appliances mandating that products sold after July 1, 1992, emit no more than 4.1 grams of particulate matter per hour for catalytic equipped units and no more than 7.5 grams for non-catalytic equipped units.

EQUIVALENT VENT LENGTH—Method for determining pellet venting size for positive pressure venting systems that takes into account the factors that affect air flow.

ETHANE—A hydrocarbon compound found in natural gas.

EXCESS AIR—Air in the firebox or fire chamber of a solid fuel appliance that is not used in combustion reactions (and exhausts through the venting system).

EXPANSION JOINT—Joint or separation made between different materials that have different expansion rates, as between a concrete floor and a column base or wall. A filler strip is placed in the joint. The term is used in relation to brick building units.

EXPLOSION—Rapid burning with an improper rate of air and fuel; not under control and with excessive pressure.

FACTORY BUILT FIREPLACE—Prefabricated metal fire chamber and its chimney, commonly called zero clearance. Consists of listed manufactured components that are assembled in accordance with the terms of the listing to form the completed fireplace.

FACTORY-BUILT CHIMNEY—A chimney composed entirely of listed manufactured components, designed to be assembled as an entire system in accordance with the terms of the listing.

FINES—Small, dust like particles produced in the pellet manufacturing process and in break down during shipping and handling


FIRE RESISTANCE RATING—The time a material will withstand, without igniting, flame and heat as specified by code and specific test conditions.


FIREBRICK—Brick capable of withstanding high temperatures, such as in stoves, furnaces and boilers. Different types of firebrick have different temperature limits.


FIRECLAY—A kind of clay capable of withstanding high temperatures while maintaining its original shape and size; fire clay products are resistant to corrosion, softening, or cracking. NFPA recommends that fire clay chimney flue liners resist corrosion, softening, or cracking from flue gases at temperatures up to 1800 degrees F. Used for flue liners for masonry chimneys.

FIREPLACE—An enclosure, open in the front for burning fuel. Solid fuel fireplaces may contain and vent gas log sets or fireplace inserts. Gas fireplaces are metal appliances open in the front and containing artificial log sets.

FIREPLACE INSERT—Solid fuel appliance designed to be installed partially or fully in the firebox of a masonry fireplace, and which vents into the fireplace chimney by means of full relining or appliance to flue methods.

FIREPLACE STOVE—A free-standing solid fuel burning room heating appliance operated either with its fire chamber open or closed to the room. NFPA and most codes use the term room heater-fireplace stove combination for a fireplace stove, and use the term fireplace stove to designate a unit without doors, that has its fire chamber always open to the room.

FIREPLACE, ZERO CLEARANCE—A factory-built metal fireplace with multi-layer construction providing enough insulation and/or air cooling so that the base, back, and in some cases sides, can safely be placed in direct contact (zero clearance) with combustible floors and walls.

FIRESTOP—A noncombustible barrier, often metal, placed to span the air space between the outer walls of chimneys and surrounding combustibles; serves to resist the spread of fire between floors of a structure.

FLAGSTONE—A natural flat stone used in walkways and fireplaces. One stone is a flag.

FLAME IMPINGEMENT—The striking of flame against an object, such as flame impingement on the catalytic combustor.

FLAME RECTIFICATION—Means to ensure gas shutoff in the absence of flame in electronic ignition systems. Alternating current applied to an electrode engulfed in the pilot or burner flame is rectified, or changed to direct current, to power a control module that maintains gas flow until the flame is extinguished.

FLAMMABILITY LIMITS—Minimum and maximum amounts of fuel (expressed as a percentage) in an air and fuel mixture within which combustion can take place.

FLASHING—Sheet metal or plastic used at breaks in a abuilding where water might leak in. Flashing is run under the building material to create a barrier.

FLOOR PROTECTION—Noncombustible material, of specified size, thickness, material and conductivity placed under a solid fuel appliance; required to extend beyond the four sides of the appliance. Serves to protect combustible floor surfaces and framing. differs from Hearth.

FLOOR PROTECTION—Noncombustible material, of specified size, thickness, material and conductivity placed under a solid fuel appliance; required to extend beyond the four sides of the appliance. Serves to protect combustible floor surfaces and framing. Differs from hearth.

FLUE—The passageway in a chimney for conveying flue gases to the outside atmosphere

FLUE COLLAR—The part of the solid fuel appliance which accepts the chimney connector. The flue collar diameter or dimension is designed by the appliance manufacturer to adequately accommodate the flow of gases out of the appliances.

FLUE GASES—The gases in an operating venting system, consisting of combustion products plus whatever air is mixed with them. Essentially synonymous with smoke and stack gases.

FLUE LINER—Usually a high temperature clay (fireclay) round or rectangular sleeve lining the interior of masonry chimneys. Although not recognized by many building codes, other materials such asFLY ASH—Ash that goes up the chimney, as opposed to ash that remains in the fuel burning appliance.

FOOTING—Support for wall, column, or pier.

FRACTIONATING—Extraction of impurities and hydrocarbons from wet and natural gas.

FREESTANDING GAS APPLIANCE—An appliance with gas burning log set that has the appearance of a solid fuel appliance that is placed away from walls in a dwelling.

FREESTANDING STOVE—Heating appliance normally on legs or a pedestal that occupies an area roughly equal to that of an easy chair.

FULL RELINING—A means of venting a solid fuel appliance (including fireplace inserts) into fireplace chimneys; the listed liner extends from the appliance out the top of the chimney and includes insulation and components in accordance with the terms of the listing. Also referred to as positive connection.

FURNACE—A central heating appliance that supplies hot air, through ducts, to the house.

FUSE—A device containing an element that protects an electric circuit by melting to open the circuit when overloaded.

FUSED ASH—Ash and impurities such as silica that melt and stick together.

FUSION POINT—The temperature at which ash and silica liquefy and melt together to form clinkers. Varies greatly according to composition, particularly chloride content.

GAS COCK ASSEMBLY—Part of the combination valve that is a multi-positioned and tapered valve designed to allow or shut off gas supply to the appliance. Also known as valve control.

GAS FIREPLACE INSERT—A gas appliance designed to be installed within an existing fireplace. Usually gas logs within a metal enclosure that surrounds the logs and covers the space between itself and the fireplace opening.

GAS LOGS—An open flame type appliance consisting of a burner and metal pan or base supporting simulated logs. May include various ember media.

GAS VENT—A factory made, listed venting system designed to remove flue gases to the outside atmosphere. See direct vent and Type B vent.

GLASS DOORS—Used with an open fireplace to reduce draft when fireplace is not in use.

GLASS DOORS—Used with an open fireplace to reduce air flow.

GRATE—A metal plate with engineered holes or a framework of metal bars used to hold fuel in the burn pot and to allow ashes to drop through to the ash drawer.

GRAVITY VENT—Type of venting that uses the natural draft of a column of warm gases rising due to the pressure of surrounding cooler air.

GROUNDED—The metallic connection of an electric circuit to the earth by means of a water main or special rod driven into the ground

GROUT—Mortar of pouring consistency used to fill masonry voids in building units or to fill between masonry walls. A liquid mortar. Made of portland cement, lime, aggregates, and water.

HEARTH—The floor of the firebox, most commonly used in reference to fireplaces. More generally, the foundation upon which fires for aesthetic and heating purposes are built. Differs from floor protection.

HEARTH—The fire resistant surface under your stove, often made of brick, or tile.

HEARTH EXTENSION—Noncombustible floor protection extension beyond the opening of a fireplace or stove. The term is also sometimes used to denote the floor protector under or around any residential solid fuel burning appliance.

HEAT LIFE (THERMAL CAPACITANCE)—The length of time a stove stays hot after burning a load of fuel.

HEAT LOSS CALCULATION—Calculation to determine house btu loss; factors include conduction through construction materials, air infiltration losses and the difference between actual or projected outside temperatures and desired temperatures inside the house. Used for determining necessary heat output from the heating appliance.

HEAT OUTPUT—The amount of usable heat produced by a heating appliance; expressed in btu (for solid fuel and most conventional fuel appliances) or watts per hour.

HEAT SHIELD—Refers to a non-combustible protector used around appliances, or smoke pipe.

HEAT TRANSFER EFFICIENCY—The percentage of heat, which is released in the fire, that gets through the appliance and chimney walls to become useful heat in the house.

HEAT VALUE—Amount of heat potential of one cubic foot of gas when burned. Also known as calorific value.

HIGH LIMIT SNAP SWITCH—A control device, or normally closed switch, which shuts down operation either of all motors or just the auger motor when excessively high temperatures are reached by opening to interrupt the flow of electrical current to the component(s).

HOPPER—Container attached to an appliance in which fuel, either coal, nuggets, or wood pellets, is stored and from which the fuel is fed to the burner.

HOPPER—container that holds the fuel supply

HOT AIR PLENUM—Sheet metal chamber mounted to the furnace, into which hot air is directed, and to which ducts are attached for hot air distribution into the house.

HOT JUNCTION—Joined, heated end of thermocouple/thermopile.

HOT SURFACE IGNITION—Type of electric (intermittent) ignition system in which a glow bar is heated by electrical means to a temperature of about 2500 degrees F. to provide the heat to ignite main burner gas.

IGNITION SYSTEMS—Devices that ignite the pilot burner and or the main burner assembly.

IGNITION TEMPERATURE—The lowest temperature at which combustion occurs. Varies widely with reference to the variety of flammable gases spontaneously combusting in a solid fuel appliance.

INCOMPLETE COMBUSTION—Improper air/fuel mixture or inadequate temperatures resulting in less than complete burning of fuel. May produce aldehydes and or carbon monoxide.

INCREASER—Chimney connector component which permits the transition from smaller to larger connector, thimble, liner or chimney.

INFRARED RADIATION—The invisible and harmless radiation emitted by a hot object. This radiation is converted into heat when it is absorbed.


INSULATING BRICK—Low density (high porosity), low thermal conductivity firebrick intended for use in kilns and furnaces to insulate them, reducing heat losses. Its conductivity and its Heat Storage capacity are both 1/5 to 1/3 that of hard firebrick.

INSULATION—Material that resists heat flow, used on masonry wall to help prevent heat loss or heat gain.

INTERMITTENT IGNITION SYSTEM—Means of lighting the pilot or main burner without the use of a standing pilot, or main burner without the use of a standing pilot, by electronic spark or hot surface ignition. Also known as electronic ignition device.

ISLAND FIREPLACE—Fireplace that has four sides of glass, for viewing from any angle.

JOINT COMPOUNDS—Non-hardening materials used on pipe threads to insure a proper seal.

K VALUE—Indicates the amount of BTUs of heat that will flow in one hour through one square foot of a uniform material one inch thick for each degree Fahrenheit of temperature rise. Used in calculating floor protection materials and thickness when one noncombustible material is used.

KINDLING—Thin, dry wood used to start a fire.

LABELED—Equipment or material identified as having undergone approved inspection and compliance manufacturing and performance procedures.

LEAKAGE TESTING—Procedure to ensure that there is no uncontrolled flow of fuel gas in the gas piping system and or the appliance.

LIFTING FLAMES—An unstable burner condition in which flames rise above or blow off the burner port.

LIMIT SWITCH—Bimetallic device designed to react to excessive temperature by causing gas flow to be cut off.

LIQUEFIED PETROLEUM GAS (LPG)—Colorless, odorless, and non-toxic gas separated from wet natural gas, light crude oil, and oil refinery gases. Composed predominantly of following hydrocarbons or mixtures thereof: propane, propylene, normal butane or isobutane and butylenes.

LIQUID PROPANE—Liquified petroleum gas, available in cylinders, for home use.

LISTED—Included in a list published by a recognized testing laboratory or inspection agency, indicating that the equipment meets nationally recognized safety standards.

LOW LIMIT SNAP SWITCH—A control device or normally open switch, which shuts auger and blower motors down if minimum operating temperatures are not reached or sustained. Also known as safety disc.

MAIN GAS BURNER—Device for the final conveyance of gas or a mixture of gas and air to the combustion zone. Consists of burner orifice, air shutter, mixer, and burner head.

MANIFOLD—The conduit of an appliance which supplies gas to the individual burners.

MANIFOLD PRESSURE—Gas pressure between the combination valve and the burner orifice.

MANOMETER—Instrument used for measuring the pressure of gases.

MANTEL—Shelf over and above the fireplace opening. Stone, brick or wood may be used.


Manufacturers INSTALLATION INSTRUCTIONS—Instructions and recommendations for proper assembly, adjustment, and installation of listed equipment.

MASONRY CHIMNEY—Chimney constructed on site of masonry and fire clay materials; construction requirements specified by code. Also refers to existing masonry chimneys of various constructions.

MECHANICAL DRAFT—induction of combustion air and removal of flue gases by means of an electric blower

MECHANICAL SIDEWALL VENTING—Totally horizontal through the wall venting of combustion by products under positive pressure by means of an electric fan. Commonly referred to as direct vent, but termination conditions differ. See Direct Vent.

METHANE—Main constituent of natural gas. Chemical formula CH4.

MILLIVOLT (MV)—Unit of electromotive force equal to one one-thousandth of a volt.

MIXER—Component of a main burner where gas mixes with air. Consists of mixer face, mixer head, and mixing tube (venturi).

MOBILE HOME APPLIANCE—Solid fuel appliance specifically designed to meet HUD standards for installation into mobile homes. Includes outside combustion air, floor mountings, substantially reduced clearances, and designated venting systems.

Moisture Content—The percentage of the fuels weight that is water in comparison to the total weight of the water and wood in the wet method; in comparison to the weight of the oven dried fuel in the dry basis.

MULTI-METER—A device consisting of one or more meters used to measure two or more electrical quantities in an electrical circuit, such as voltage, resistance, and current.

MURIATIC ACID—Acid solution used for cleaning masonry work. A solution of hydrochloric acid.

NATIONAL FUEL GAS CODE (ANSI Z23.1, NFPA 54)—A standard for the installation of gas appliances, piping and venting.

NATURAL GAS—Colorless, highly flammable gas found in porous geologic formations beneath the earths surface. Consists mainly of methane.

NFPA—The National Fire Protection Association, 470 Atlantic Avenue, Boston, MA 02210. An independent not-for-profit organization for fire safety.

ODORANT—Material added to natural gas or LPG in small concentrations to impart a detectably distinct odor. Usually mercaptan.

OPACITY—Thickness of smoke. An indicator of combustion efficiency.

ORIFICE—The opening in a cap, spud, or other device whereby the flow of gas is limited and or controlled and through which the gas is discharged to either a pilot burner or main burner.

ORIFICE SPUD—A removable plug or cap containing an orifice.

OVEN DRY WOOD—Wood dried at 217 degrees F. to a constant weight; defined as having zero moisture content.

PARGING—Process of applying a coat of mortar to masonry construction, especially used for masonry walls. Also the cement mortar coat itself.

PARTICULATE MATTER—Tiny pieces of condensable hydrocarbons in solid or liquid form. The basis of solid fuel emissions regulations of the Environmental Protection Agency.

PARTITION—The masonry wall that must separate flue liners in a masonry chimney. Also referred to as Wythe.

PELLETS—A compressed, cylindrical fuel made from wood by products (such as from a furniture mfg.) for use in a specially designed stove.

PENINSULA FIREPLACE—A fireplace that has three sides of glass.

PIEZO IGNITOR—A device which delivers an igniting spark by means of pressure on a crystal.

PILOT—A small flame used to ignite the gas at the main burner. May be standing (constantly burning) or intermittent (on demand for heat).

PLINTH—Base-Usually square in shape.

POINTING—Filling mortar into the joint with a trowel after the masonry units are laid; filling of raked out joints.

PRESSURE ADJUSTMENT SCREW—Part of a pressure regulator located directly under a cap screw on top of the regulator. Means of adjusting gas pressure on some regulators. Note: some pressure regulators are not subject to adjustment. Check manufacturers instructions.

PRESSURE REGULATOR—A device for controlling and maintaining a uniform outlet gas pressure. Service regulators reduce high street pressure of natural gas or reduce LPG storage tank pressure. Appliance regulators, usually part of the combination valve, reduce, adjust and maintain constant pressure to be used in an appliance.

PRESSURE TEST—Method of checking for leaks in the gas supply line prior to installation of appliances

PRIMARY AIR—Combustion air directed to the firebox where the fuel is located; supports all stages of combustion

PRIMARY COMBUSTION—The burning of solid wood and some of the combustible gases, which takes place in that portion of the appliance where the wood is. The distinction between primary and secondary combustion is somewhat artificial.

PROPANE—A colorless, odorless, nontoxic LPG containing more heat value than natural gas.

PSI—Pounds of pressure per square inch.


PYROLYSIS—Chemical alteration of wood, coal, or other combustible materials as a result of the application of heat. Stage of wood combustion during which wood molecules decompose into wood oil vapors and gases. The products of pyrolysis are gases, tar fog and charcoal or coke.

R-VALUE (RESISTANCE VALUE)—A measure of how resistant a substance is to transferring heat.

RADIANT STOVE—A stove whose heat output is mostly in the form of radiant energy. The exterior of the stove is tremendously hot and room air circulates around the body of the stove giving off heat.

RADIATION—Heat that moves out in waves from a central point and heats objects in its path. The closer you get to a source of radiant heat the more heat you will feel.

REDUCER—Chimney connector component which permits the transition from a larger to smaller diameter chimney connector, thimble, liner or chimney. Not normally recommended because of potential smoke spillage and poor appliance performance.

REFRACTORY—Any solid ceramic material suitable as a structural or protective material at high temperatures in a corrosive environment.

REFRACTORY MORTAR—High temperature masonry mortar used primarily to join flue liners. Required by NFPA as medium duty, non water-soluble calcium aluminate refractory cement mixture, or its equivalent.

RELINE—An inner chimney made of metal or refractory material, usually with added insulation, that fits inside an existing chimney. Usually installed for improved safety and efficiency when a chimney is inappropriate or oversized for a heating stove.

RESIDENCE TIME—The amount of time the subject matter remains in the zone of reference, as in the residence time of gases in the fire chamber.

SAFETY PILOT SHUTOFF VALVE—A component of the pilot or the combination gas valve that allows or shuts off gas flow on the basis of the presence or absence of flame. Consists of a u-shaped electromagnet (see solenoid), gas shutoff disc, tension spring, keeper plate, thermocouple/thermopile connection, and a reset button. Also known as millivolt system and electromagnetic power unit (EPU).

SAFETY SHUTOFF—A device, usually powered by a thermocouple/thermopile, designed to shut off the gas supply to the pilot and or main burner if the source of ignition fails

SEASONED WOOD—Wood that has lost a significant amount of its original (green) moisture. The term has no both quantitative and universally accepted meaning.

SEASONED WOOD—Refers to fuel wood that has been allowed to dry before burning. Seasoning generally takes six to 12 months. Woods burns much easier when its moisture content has been reduced. Freshly cut wood contains over 20 percent water.

SECONDARY AIR—Combustion air directed downstream of the primary combustion zone (but still in the appliance) to support the combustion of remaining combustible gases; does not directly influence the rate of primary combustion.

SECONDARY COMBUSTION—The burning of the combustible gases and smoke which are not burned in primary combustion.

SECONDARY COMBUSTION CHAMBER—The place where secondary combustion occurs.

SEDIMENT TRAP—In gas piping, a tee device to intercept or hold solid foreign particles to prevent them from blocking valves or orifices. If not part of an appliance, must be installed as close to appliance inlet as possible.

SILICONE SEALANT—Process of sealing cracks with a high temperature silicone sealant.

SMOKE—The visible portion of flue gases composed of solid, liquid and gaseous products of combustion. Commonly used to refer to all exhaust from solid fuel burning.

SMOKE CHAMBER—The transition zone between a fireplace throat and fireplace chimney, extending from the damper or throat to the base of the first flue.

SMOKE SHELF—The ledge directly behind the throat of the fireplace, at the base of the smoke chamber.

SMOKE TEST—A test to determine chimney leakage; a small smokey fire is built, or an activated smoke candle is placed in the appliance after which the chimney top is obstructed. The smoke is consequently forced through the chimneys points of leakage. Required by NFPA 211 after construction and before use of the masonry chimney.

SMOKE TEST—Checking a masonry fireplace and chimney by building a fire in the fireplace and closing the flue top. Smoke will flow out of any cracks or openings.

SOAPSTONE—A metamorphic rock (steatite) known for its ability to withstand direct flames and to retain heat.

SOLENOID—Coil of wire which pulls an iron core within it magnetically when electricity flows through it. In use, known as electromagnet.

SOLID FUEL—Wood, coal, and other similar organic materials in various forms (e.g. chunk wood, pressed logs, wood pellets, wood chips, paper, processed coal, coke, peat, charcoal)

SOOT—Soft, black or brown velvety deposit of carbon particles inside appliances, chimneys, and connectors. Soot originates in oxygen-poor flames.

SOUR GAS—Gas containing amounts of sulfur that prevent its use as a fuel unless purified

SPARK ARRESTER—A noncombustible screen installed between the top of the chimney and the underside of the chimney cap; prevents the escape of sparks and burning materials from the chimney.

SPECIFIC GRAVITY—The weight of one substance compared to the weight of another substance, both of equal volume and measured at the same temperature and pressure.
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