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A direct vent fireplace is a prefabricated metal fireplace that employs a direct-vent combustion system. "Direct vent" refers to a sealed-combustion system in which air for combustion is drawn from the outdoors, and waste combustion gasses are exhausted to the outdoors. "Direct vent" does not simply mean that all gasses from combustion are vented to the exterior of the structure in which it is installed. [1] [2]
The preassembled fireplace unit is made up of two main components: the outer housing, and the flue system.
The outer housing is the part of the fireplace unit that is installed in the framing of the building. The two main operational components are housed inside of it. The first key component within the outer housing is the firebox, which is surrounded on five sides by the outer housing, and on one side by the glass panel that faces towards the room. This is the space in which the fire burns during operation. Because of this, the gas burners (either natural gas or propane) are located inside of the firebox. To provide a more realistic look, imitation logs and ember material are placed on top of the burners. The ember material, which will not burn, is designed so that it will glow like real embers when heated. The firebox is designed to be smaller than the outer housing so that there is an empty space between the outermost walls of outer housing and the outer walls of the firebox. The empty space in between the firebox and the outer housing is the second important operational component of the outer housing. This space is filled with air from the interior of the room being heated and is used to add hot air to the room without the addition of exhaust gasses from combustion. [3]
The flue system is composed of two flues, the inner flue and the outer flue. The outer flue draws air into the bottom of the sealed firebox to allow for combustion. The inner flue draws hot exhaust gasses from the top of the sealed firebox and vents them directly to the outside of the structure through either an adjacent wall or roof. [4]
To begin the operation of the fireplace unit, the user must turn on the gas supply and ignite the burners. Once this is done, the unit will operate completely autonomously until the gas supply to the burners is shut off. While in operation, convection will cause the hot air in the firebox to rise to the top of the firebox. As the amount of hot exhaust gasses increases from the combustion process, the hot gas at the top of the firebox is eventually pushed out through the inner flue. At the same time, the removal of the exhaust gasses through the inner flue allows for relatively cold air to be drawn into the firebox through the outer flue. [5]
As the firebox heats up due to the operation of the burners, it radiates heat into the room through the porous glass face that separates the firebox from the inside of the room. At the same time, it transfers heat through the surrounding metal walls into the empty space between itself and the outer housing. This heat transfer creates a convection process inside of the empty space that is very similar to the one that takes place inside of the firebox. Built into the design of the room facing side of the unit are two vents, one at the top and one at the bottom. Once the air in the empty space begins to heat up, convection pushes this heated air further up in the chamber until it is eventually pushed out through the top vent. This phenomenon works in the same way to draw air in through the bottom vent. As the hot air is pushed out, space is emptied in the chamber behind the firebox, which then draws cold air in through the bottom vent. [6]
Both of these convection processes immediately begin to slow down, and eventually stop, as soon as the burners turn off. [7]
Direct vent fireplaces are extremely efficient compared to a traditional fireplace and can operate at about 85% efficiency. Even a very efficient traditional fireplace only operates at about 15% efficiency. This is because most of the hot air generated by the fire travels up the chimney due to convection. A traditional fireplace can also draw hot air in from the room and expel it through the chimney, further lowering the efficiency. The design of the direct vent fireplace allows for such a high level of efficiency because of the sealed firebox. The sealed firebox only allows combustion gasses to leave the system and exit the building. Since it is sealed, no warm air from the room is able to be drawn into the firebox and expelled out of the building. [8]
Direct vent fireplaces operate off of propane or natural gas, and are completely sealed from the interior of the building in which they are installed. Thus, no harmful byproducts are released into the room. They also release much less pollution into the atmosphere than a wood-burning fireplace. [2]
A boiler is a closed vessel in which fluid is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.
A furnace, referred to as a heater or boiler in British English, is an appliance used to generate heat for all or part of a building. Furnaces are mostly used as a major component of a central heating system. Furnaces are permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water. Heating appliances that use steam or hot water as the fluid are normally referred to as a residential steam boilers or residential hot water boilers. The most common fuel source for modern furnaces in North America and much of Europe is natural gas; other common fuel sources include LPG, fuel oil, wood and in rare cases coal. In some areas electrical resistance heating is used, especially where the cost of electricity is low or the primary purpose is for air conditioning. Modern high-efficiency furnaces can be up to 98% efficient and operate without a chimney, with a typical gas furnace being about 80% efficient. Waste gas and heat are mechanically ventilated through either metal flue pipes or polyvinyl chloride (PVC) pipes that can be vented through the side or roof of the structure. Fuel efficiency in a gas furnace is measured in AFUE.
A chimney is an architectural ventilation structure made of masonry, clay or metal that isolates hot toxic exhaust gases or smoke produced by a boiler, stove, furnace, incinerator, or fireplace from human living areas. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the stack, or chimney effect. The space inside a chimney is called the flue. Chimneys are adjacent to large industrial refineries, fossil fuel combustion facilities or part of buildings, steam locomotives and ships.
A stove or range is a device that generates heat inside or on top of the device, for local heating or cooking. Stoves can be powered with many fuels, such as electricity, natural gas, gasoline, wood, and coal.
A central heating system provides warmth to a number of spaces within a building from one main source of heat. It is a component of heating, ventilation, and air conditioning systems, which can both cool and warm interior spaces.
A fireplace or hearth is a structure made of brick, stone or metal designed to contain a fire. Fireplaces are used for the relaxing ambiance they create and for heating a room. Modern fireplaces vary in heat efficiency, depending on the design.
A fire-tube boiler is a type of boiler invented in 1828 by Mark Seguin, in which hot gases pass from a fire through one or more tubes running through a sealed container of water. The heat of the gases is transferred through the walls of the tubes by thermal conduction, heating the water and ultimately creating steam.
In a steam engine, the firebox is the area where the fuel is burned, producing heat to boil the water in the boiler. Most are somewhat box-shaped, hence the name. The hot gases generated in the firebox are pulled through a rack of tubes running through the boiler.
A gas heater is a space heater used to heat a room or outdoor area by burning natural gas, liquefied petroleum gas, propane, or butane.
An air preheater is any device designed to heat air before another process (for example, combustion in a boiler With the primary objective of increasing the thermal efficiency of the process. They may be used alone or to replace a recuperative heat system or to replace a steam coil.
A flue is a duct, pipe, or opening in a chimney for conveying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors. Historically the term flue meant the chimney itself. In the United States, they are also known as vents for boilers and as breeching for water heaters and modern furnaces. They usually operate by buoyancy, also known as the stack effect, or the combustion products may be 'induced' via a blower. As combustion products contain carbon monoxide and other dangerous compounds, proper 'draft', and admission of replacement air is imperative. Building codes, and other standards, regulate their materials, design, and installation.
A pellet stove is a stove that burns compressed wood or biomass pellets to create a source of heat for residential and sometimes industrial spaces. By steadily feeding fuel from a storage container (hopper) into a burn pot area, it produces a constant flame that requires little to no physical adjustments. Today's central heating systems operated with wood pellets as a renewable energy source can reach an efficiency factor of more than 90%.
A masonry heater is a device for warming an interior space through radiant heating, by capturing the heat from periodic burning of fuel, and then radiating the heat at a fairly constant temperature for a long period. Masonry heaters covered in tile are called cocklestoves. The technology has existed in different forms, from back into the Neoglacial and Neolithic periods. Archaeological digs have revealed excavations of ancient inhabitants utilizing hot smoke from fires in their subterranean dwellings, to radiate into the living spaces. These early forms have evolved into modern systems.
A kerosene heater, also known as a paraffin heater, is typically a portable, unvented, kerosene-fueled, space heating device. In Japan and other countries, they are a primary source of home heat. In the United States and Australia, they are a supplemental heat or a source of emergency heat during a power outage. Most kerosene heaters produce between 3.3 and 6.8 kilowatts.
Condensing boilers are water heaters typically used for heating systems that are fueled by gas or oil. When operated in the correct circumstances, a heating system can achieve high efficiency by condensing water vapour found in the exhaust gases in a heat exchanger to preheat the circulating water. This recovers the latent heat of vaporisation, which would otherwise have been wasted. The condensate is sent to a drain. In many countries, the use of condensing boilers is compulsory or encouraged with financial incentives.
Forced-air gas heating systems are used in central air heating/cooling systems for houses. Sometimes the system is referred to as "forced hot air".
A wood-burning stove is a heating or cooking appliance capable of burning wood fuel, often called solid fuel, and wood-derived biomass fuel, such as sawdust bricks. Generally the appliance consists of a solid metal closed firebox, often lined by fire brick, and one or more air controls. The first wood-burning stove was patented in Strasbourg in 1557. This was two centuries before the Industrial Revolution, so iron was still prohibitively expensive. The first wood-burning stoves were high-end consumer items and only gradually became used widely.
A rocket mass heater (RMH), also known as rocket stove mass heater, is a form of slow-release radiant heating system, designed to primarily heat people and secondarily to warm areas in line of sight around it. Variations of RMH can also be extended for the functions of cooking, heating water, and producing warm air for distribution.
A storage water heater, or a hot water system (HWS), is a domestic water heating appliance that uses a hot water storage tank to maximize water heating capacity and provide instantaneous delivery of hot water. Conventional storage water heaters use a variety of fuels, including natural gas, propane, fuel oil, and electricity. Less conventional water heating technologies, such as heat pump water heaters and solar water heaters, can also be categorized as storage water heaters.
An industrial furnace, also known as a direct heater or a direct fired heater, is a device used to provide heat for an industrial process, typically higher than 400 degrees Celsius. They are used to provide heat for a process or can serve as reactor which provides heats of reaction. Furnace designs vary as to its function, heating duty, type of fuel and method of introducing combustion air. Heat is generated by an industrial furnace by mixing fuel with air or oxygen, or from electrical energy. The residual heat will exit the furnace as flue gas. These are designed as per international codes and standards the most common of which are ISO 13705 / American Petroleum Institute (API) Standard 560. Types of industrial furnaces include batch ovens, metallurgical furnaces, vacuum furnaces, and solar furnaces. Industrial furnaces are used in applications such as chemical reactions, cremation, oil refining, and glasswork.