The 10 Major Items of a Real Masonry  Fireplace

By: Charles W. Ostrander, Executive  Director

This is not an all inclusive list of all requirements  to meet Building Codes, but is a primer on major items to help  avoid problems

1.  THE BASICS

Is the fireplace even drawn on the  drawings?  Or is there just an arrow calling out a  "fireplace"?  You should at least have the  following on the drawings:

• The size of the fireplace
• The fireplace opening dimensions
• A cross section and a cut shown
• Size of the hearth, it's depth and  how it is supported
• Size of the flue
• How is the cap installed?
• How is the chimney counterflashed  into the roof?
• Show cricket or saddle, if required

2. THICKNESS AND CONSTRUCTION OF FIREBOX  WALL (FOR FIRESAFETY)

3. DAMPER CLEARANCE

The metal damper is required to be a  minimum of 8" above the top of the fireplace opening.   I suggest, to minimize possible excessive smoking, to  place the damper an additional 4 inches high for a total of  12" above the fireplace opening. \

4. Chimney Clearances

Any portions of a masonry chimney located  in the interior of the building or within the exterior wall of  the building shall have a minimum air space clearance to  combustibles of 2 inches.  Chimneys located entirely  outside the exterior walls of the building, including chimneys  that pass through the soffit or cornice, shall have a minimum  air space clearance of 1 inch.  The air space shall not be  filled , except to provide fire blocking.

5. Flue liners

Fireplace Chimneys with clay flue liners  must be enclosed with 4" of solid masonry.  If  multiple fireplaces are vented in a common masonry flue stack,  each flue should be supported and separated by 4" of masonry from top  to bottom, between the flues vertically.(maximum slope of flue  is no greater than 30 degrees from vertical.)

6. Hearth Information

Hearth extension (from the front of  fireplace opening)

• 16" if fireplace opening is less than  6 square feet
• 20" if fireplace opening is greater  than 6 square feet

Hearth extension (from each side of  opening) 8" if fireplace opening is less than 6 square  feet

• 12" if fireplace opening is greater  than 6 square feet

7.  Flue size

I prefer a slightly oversized flue instead  of an undersized flue (for initial startup reasons).  You  can always damper down the flue opening - but you cannot draw  more air once the damper is open 100%.  Here are some of  the most common fireplace opening / flue sizes:
note - for a corner fireplace where the  flue is offset at an angle (max. 30 deg. from vertical) to get  the flue to the outside, use the next largest flue size

8. Energy Efficiency
 

 A. Use outside air for combustion  kits built into the hearth with the outside air vents just  inside the front of the fireplace. (if air kit is  a retrofit or an afterthought, put a circular pipe vent into  the back or side wall of the fireplace)

 B. Use sealed, glass fireplace  doors.

9. For convenience

Install a log lighter, unless you were an  Eagle Scout.  You'll have more fires and enjoy your  fireplace more.  Also, install an ash caddy dump into your  hearth for ease of ash removal.

10. Install a spark arrestor for your  chimney

The major reason in the midwest is to  prevent rain from going down your flue and possibly causing a  damp smell - but a good metal chimney cap also prevents Rocky  Racoon or a grey squirrel from taking up residence with other  associated problems.
 

Click here for more info on chimney cap construction