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How Does A Zero-Clearance Fireplace Work?

How Does A Zero-Clearance Fireplace Work?-Fast Replacement Glass answers your questions!While everyone loves to snuggle up with a good book or watch a rainy-day flick by the fireplace, it's all the more comforting when you can rest assured that your zero clearance fireplace is operating properly. This means ensuring the flames are contained to the firebox while smoke and hot gases are encouraged to exit up through the ventilation system. There is a science to the construction of your prefab fireplace. Let's begin with the hearth and work our way up. 

  • Hearth. This area extends beyond the fireplace and is made from fireproof materials. It can be a tiled surface that is flush with the floor or a refractory brick ledge. With factory built fireplaces, a hearth is not a requirement, but many homeowners prefer to add one for aesthetics.
  • Facing, Fireplace Doors, & Mesh Screens. When you think of a fireplace, these attractive items usually come to mind first. They are meant to flatter to their surroundings. The facing protects the wall surrounding the firebox, and can be customized to meet a number of different décor styles. Brick, stone, river rock, wood, and drywall are all acceptable materials. Fireplace doors help prevent cold air from entering the room when your fireplace is not being used. They are a beautiful way to enhance the look of your prefab unit, while keeping your home and loved ones safe from flames and embers. Steel mesh screens provide a layer of protection against sparks, and come in a variety of styles and colors.
  • Firebox. This is the metal housing that is installed within non-masonry walls where the fire is tended and enjoyed. Its proportions should be relative to the size of the room in which it will be placed. For example, add one inch to the width of the firebox opening for every foot of room space. Otherwise, you could have a firebox that is either too big and expensive to heat, or too small to provide comfortable warmth for the space in which it resides. Smoke that is produced from a wood burning fire is collected here and then pushed up and out of the ventilation system.How does a zero clearance fireplace work? Fast Replacement Glass explains it!
  • Double-Walled Pipe. This “pipe within a pipe” is the ventilation system that is used with a factory built fireplace. Remember: prefab fireplaces are just a firebox. They are not conjoined with the flue as a masonry fireplace is. Therefore, the outgoing smoke and gases need to be contained so that they are not freely moving inside the chimney or walls and potentially leaking into the home. This unique vent system is constructed of an inner (primary) pipe and an outer (secondary) pipe. The primary duct is responsible for transporting smoke and hot gases out of the firebox, while the secondary pipe is utilized for containment. This construction ensures an added measure of safety – if the inner pipe were to fail and and emit smoke and gases, the fumes would be trapped and rerouted by the outer encasing.
  • Firestop. Harmful gases and smoke can permeate through openings in ventilation systems. In order to prevent this from happening, firestops serves as barriers for these breaches. Mandatory firestops (also commonly referred to as joist shields) are UL approved and usually constructed from galvanized steel. These shields are required in areas where a chimney passes between two living spaces or an occupied attic space. Therefore, depending on which floor your fireplace resides, you may need more than one firestop.
  • Flashing. Moisture from condensation and rain can be easily prevented with flashing. This metal strip is used at the junction of the roof and chimney to prevent water from entering and damaging the roof.
  • Chimney Cap. Even though a chimney is not necessary with this style of fireplace, a chimney cap is essential for keeping debris, wind gusts, rain water, and animals out of the stove pipe. It is usually constructed from stainless steel.

Now let's delve more into how these prefab fireplaces work. As you know, they are factory built from sheet metal or cast iron, and come ready to install in your home. They have been sufficiently insulated so that they are capable of being placed within close range of combustible materials (wood framework or drywall) and do not require a masonry surround.

  • Zero-clearance fireplaces work via piping.
    Each manufacturer utilizes double or triple wall pipe that is custom fabricated for their fireplaces. (For example: you cannot get a zero clearance fireplace from one manufacturer and expect to use the piping from a completely different manufacturer.) It is not uncommon for high-end zero clearance fireplaces use Class A stainless steel chimney pipe.
  • A blower unit recirculates heated air into your living space.
    Certain models utilize a valve that controls air flow into the firebox, which further controls the burn rate and amount of heated air that is released. Zero-clearance fireplaces are known for their efficiency rating, with provides up to 70% more heat than traditional masonry fireplaces

Additionally, there are a variety of fuel sources for zero-clearance fireplaces. The most common are gas burning applications; however, some units are designed to burn wood, and there are even electric fireplaces available.

  • GAS
    Whether you choose natural gas or propane, a gas fireplace heat the room that it is situated in by way of force. This elminates heat loss via the chimney and allows the fire to have a lower combustion fuel rate and increased efficiency. The fuel pipe simply needs to be engaged when getting ready to start and burn a fire. Gas fireplaces have a valve that controls the pressure and amount of gas supplied to the unit. Some valves have the ability to detect whether or not gas is being heated. Ignited gas has an increase in temperature, and once it reaches a certain point, the gas valve cuts off the suppy. This safety feature helps prevent harmful fumes from escaping into the home. There are vented and ventless gas fireplaces.
    • Ventless: this is similar to a gas range on a cookstove. These clean burning units do not require a chimney or ventilation pipe. Heat is forced into the room, and these highly efficient fireplaces use substantially less fuel to produce warmth.
    • Vented: an exhaust pipe is vented directly through the wall of a home, similar to a dryer vent. In some cases, a centrally placed unit may be vented through the roof. Vented gas fireplaces are completely sealed. They draw air in from the outside for combustion purposes, and then vent it back outside. Therefore, the only thing that enters the home is heat.
  • WOOD
    Cool air enters the firebox and feeds the fire through combustion. Smoke and gases that are produced from this process escape via the chimney. Heat that is generated will radiate into the room in which the fireplace is situated. This fire will need constant tending with wood and kindling. 
    These particular fireplaces have metal coils that heat up when the application is plugged into an electrical socket. A blower motor or fan pushes the 10% of the heat that is generated outward into the home. These fireplaces are cool to the touch, posing no threat to curious little hands. The "flames" are produced by a standard light bulb and refracted light in a three-dimensional pattern, simulating a very realistic look!
Last updated on July 28th 2017.

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