Following are some terms and their definitions to help you understand what vendors may say. It is helpful to be familiar with firplace related terms.
AFUE - Annual Fuel Utilization Efficiency. An official heat source measurement rating for fireplaces and wall heaters.
BTU - British Thermal Unit. This is the common way in which heat is measured. A BTU is the amount of thermal energy needed to raise the temperature 1 pound of water by 1 degree Fahrenheit. Despite its name, the unit is used universally in the United States and only sometimes in Britain.
Carbon Dioxide - Sometimes referred to as CO2. Carbon dioxide is a gas that is produced with complete combustion of carbon units. It is not generally dangerous in the amounts produced.
Carbon Monoxide - Sometimes referred to as CO. Carbon monoxide is produced by incomplete combustion of carbon. It is colorless, odorless, and deadly even in relatively small quantities if there is not good ventilations.
Catalytic Combustor - A device used in some wood burning stoves to reduce the temperature at which smoke is ignited.
Clearance - The distance required by building and fire codes between a portion of the fireplace unit, including pipes and chimney, and combustible materials.
Chase - A decorative surrounding that covers the metal flue inside the chimney.
Chimney Cap - A vented cap placed on top of a chimney to prevent obstructions such as leaves and bird nests. A chimney cap can also protect the chimney top from gusts of wind that will interfere with the draft.
Chimney Pot - A decorative pot set at the top of a chimney that can extend the chimney's length and improve its draft.
Creosote - A flammable by-product of combustion that condenses on the inside of chimneys increasing the risk of chimney fires.
Damper - A device used to close off a flue or chimney when not in use and to allow air in when a fire is going. Most dampers are installed at the base of the flue and are reachable from within the firebox.
Direct Vent - a vent system that eliminates the need for a chimney. It contains two vents, one for air intake, the other for exhaust.
Draft - The flow of air through a system. You want the draft to flow in the proper direction to take smoke and gases outside rather than venting them inside.
Fireback - A fireback shields masonry and mortar from extreme heat. Cast iron firebacks can also store the heat of the fire and radiate it into the room after the fire has gone out.
Firestop - A noncombustible device that seals openings between floors to prevent smoke or fire from penetrating from one level to the next.
Firebox - The interior portion of the fireplace where the fire is built.
Flue - Any vent or chimney that connects a combustion device with the outside.
Flue Collar - Ring on an appliance for attaching a draft hood, vent connector, or other venting system. The flue collar determines the size of the vent.
Gas Log - A manufactured log generally made from ceramic or concrete. The gas log contains the burner unit and is meant to simulate the look and feel of a genuine wooden log on fire.
Grate - An iron frame that holds burning fuel in the fireplace.
Hearth - The floor of the fireplace where the fire is built. It can also include or refer to the portion of that floor that extends into the room.
Heat Shield - A non-combustible protector for use around the appliance, chimney, or smoke pipe.
Hopper - A container for a fuel source such as wood pellets or coal that is attached to an appliance so that the fuel is fed to the burner.
Insert - A fireplace insert retrofits an existing fireplace to allow it to burn a different fuel or to make it more efficient at burning fuel or producing useable heat.
Kindling - Easily ignited material used to start a fire. Traditionally, kindling is thin, dry wood, but newspaper or other manufacture products are often used.
Mantle - (Also "mantel"). Often used to refer only to the shelf above the fireplace. Properly used to refer to the entire ornamental facing, even if it does not include a shelf.
Metal Liner - A liner placed inside an existing chimney to reduce the flue diameter and increase the speed at which smoke exits. Usually used with fireplace inserts but also used when an existing chimney is unlimited or deteriorating.
Natural Draft (B-Vent) Appliance - An appliance that takes in combustion air from the outside and vents the products of combustion back to the outside.
Natural Gas - Colorless, odorless, clean-burning fossil fuel consisting mainly of methane. This is the gas that is piped into most homes in the United States. (See also: Propane)
Pellets - Fuel source made of 100% compressed, recycled sawdust. Pellets are an efficient, clean burning energy source with only 5 to 10% moisture.
Pilot - A small, continuously burning flame that a gas appliance uses to ignite the main burner.
Propane - Liquefied petroleum gas containing more heat value than natural gas. Propane is available in cylinders for use in the home. It is colorless, odorless, and non-toxic. (See also: Natural Gas)
Safety Pilot - A safety shutoff for gas flow that provides a heat source to ignite the main burner.
Seasoned Wood - Fuel wood that has been allowed to dry for at least six months to a year before burning. Seasoned wood has lower moisture content which allows it to burn hotter, more efficiently, and with less smoke.
Spillage - A failure of the venting system that sends flue gases back into the home rather than out the vent or chimney. Combined with incomplete combustion, spillage can result in dangerous levels of carbon monoxide entering the home.
Spill Switch - A device used to detect the occurrence of spillage and alert the homeowner.
Therm - A unit of heat equal to 100,000 British Thermal Units (BTUs).
Vent Free - A device that does not draw outside air to fuel the fire and does not exhaust gases to the outside. A vent free device needs to be very efficient to avoid spilling pollutants and toxins into your living room.
Venting - The system of pipes that draws air in from the outside to aid combustion and exhausts smoke and gases to the outside.
Water Column (WC) - A measurement of gas pressure equal to one twenty-eight of a pound per square inch (PSI).
Zero-Clearance Fireplace - A factory-built fireplace that can be placed safely next to combustible material without risk of fire. These devices typically vent directly to the outside and do not require a chimney.