How to build an efficient fireplace

A fireplace can be an excellent feature in any home. Here's what you need to know about building an efficient fireplace.

How to build an efficient fireplace

Fireplaces: what are they made of?

Fireplaces and their chimneys are basically hollow towers constructed out of strong, long-lasting, heat-resistant materials such as stone, brick, mudbrick or metal.

  • They can be designed in a myriad of shapes and sizes, but no matter what they look like on the outside, all fireplaces are virtually alike inside and consist of four basic units.
  • These are the base, firebox, smoke chamber and chimney.
  • The hollow core of the chimney is called the flue.The base is the platform upon which the upper sections of the fireplace rest. It should be solid and massive in order to support the weight of the heavy masonry above it. The firebox, built on top of the base, is where the fire is set.
  • Most fireboxes are lined with a special type of brick, called firebrick, which will withstand high temperatures. The design of the firebox should allow heat generated by the fire to be radiated outward into the room, while at the same time preventing heat from escaping up the chimney in the form of hot gases.
  • The funnel-shaped smoke chamber is erected directly above the firebox. It serves as a transition unit, channelling the smoke from the fire below into the flue above.
  • The final unit, the chimney, carries the smoke and hot gases away and passes them into the atmosphere.

Building an efficient fireplace

To work efficiently, the firebox, smoke chamber and chimney need to be built in correct proportion to each other.

  • The smoke chamber should have a smooth interior surface and slope inward from its base toward the chimney opening at an angle no greater than 30 degrees from vertical. The area of the chimney opening itself should be about 10 percent of the area of the firebox opening.
  • The size of the fireplace must fit the proportions of the room.
  • Air drawn by the fire has to be replaced. In a small room the strong draft of a large fireplace will suck warm air out of the room and send it up the chimney.
  • To replace this warm air, additional air will be drawn into the room, most likely from outdoors through cracks around the windows and doors. Not only is this wasteful but the room may actually be cooler than it would have been with a smaller fireplace that drew less air.

Building a fireplace might be easier than you think. Remember this guide if you're interested in constructing one yourself.

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