One of the key aspects of residential masonry contracting is the fireplace. A properly built fireplace serves as the centerpiece of a home by bringing people together to toast occasions, relax and enjoy conversation, bask in the embers glow, or read in perfect solitude.
Fireplace design and construction comes easy to many residential contractors because they were fortunate enough to have apprenticed with a fireplace mason. It is our job to make sure that these fireplaces are built to withstand the tests of time, not just serve as objects of beautifully-crafted masonry. They must be designed and built to draw the smoke out and function as specified.
Since customers have so many choices as to how they might incorporate a fireplace into their building plans, it is vital that masons create something that is structurally sound, reflects or radiates heat efficiently, and exhausts smoke effectively. Architects are striving to create unique designs for their clients, and fireplaces are being built in an array of shapes and sizes. The efficient burning of wood has many variables; however, there are some constants in masonry fireplace design.
If the ratios and proportions of the working areas are correct, smoke and flue gases fluidly make the transition from the firebox through the damper, accelerate into the smoke chamber, and move up the flue to the top of the chimney. The entire journey must be smooth and contoured and not create eddies that inhibit the flow and cause back pressure.
It is important to understand how the masonry fireplace must be proportioned when sizing the firebox, throat, damper, smoke chamber, flue lining, chimney height, and combustion air intake. The correct ratios ensure that the fireplace will draw properly.
Architects, homeowners, and builders are always attracted to the symmetry of the Rumford fireplace and its almost square opening. This particular relationship of the opening and the effective flue size are vitally important. Generally speaking, the effective flue area should be 10% of the fireplace opening.
Knowing that you need a flue size that is equal or greater than 10% of the fireplace opening is just a start. There are hundreds of other relationships that come into play for sound fireplace construction, not just building codes to keep the heat where it belongs, or reinforcing steel to hold things together during seismic events. Flue heights, combustion air intake openings, and pressure balancing HVAC units can have enormous effects on a fireplace's operation and efficiency.
The Residential Masonry Contractors Association (RMCA) provides a place to ask any questions you might have about fireplace projects. The executive board has over 100 years of combined experience building fireplaces. We encourage the free exchange of ideas and experiences to help our fellow masons create good working fireplaces that stand the test of time.
Mike Homchick is the owner of Michael Homchick Stoneworks Inc., Kenmore, Wash. He is secretary of the Residential Masonry Contractors Association, a founding member of The Masonry Heaters Association of North America, and belongs to The Marble Institute of America.