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CHIMNEY INSPECTION DIAGNOSIS REPAIR
BACKDRAFTING HEATING EQUIPMENT
CARBON MONOXIDE - CO
CHIMNEY CAP & CROWN
CHIMNEY CLEANING PROCEDURES
CHIMNEY COMPONENT DEFINITIONS
CHIMNEY CRACK DETECTION & DIAGNOSIS
CHIMNEY DRAFT & PERFORMANCE
CHIMNEY FIRE ACTION / PREVENTION
CHIMNEY HEIGHT & CLEARANCE CODE
CHIMNEY INSPECTION, FLUE INTERIOR
CHIMNEY LEANING, SEPARATION, MOVEMENT
CHIMNEY REPAIR METHODS
CHIMNEY STAINS & LEAKS
CHIMNEY TYPES & MATERIALS
DIRECT VENTS / SIDE WALL VENTS
DRAFT REGULATORS, DAMPERS, BOOSTERS
FIRE CLEARANCES INDOORS
FIREPLACES & HEARTHS
FLUE VENT CONNECTORS
MASONRY CHIMNEY GUIDE
METAL CHIMNEYS & FLUES
SAFETY RECALLS CHIMNEYS VENTS HEATERS
SOOT AT CHIMNEY TOP
STAIN DIAGNOSIS on BUILDING EXTERIORS
WOOD, COAL STOVES & FIREPLACES
Fireplaces & hearths, construction, inspection and repair:
This article provides information about masonry fireplaces, including inspection for damage/hazards (cracks and gaps that appear at masonry fireplaces due to chimney or fireplace settlement or movement), fireplace chimney sizing requirements, draft problems, chimney safety, creosote problems, inserts, and other topics.
Fireplace damage from chimney or fireplace settlement or movement may be a fire or gas hazard in a building Fireplace hearth size specifications;
How to add support below a settling fireplace hearth Fireplace damper inspection, diagnosis, repair or replacement Photo examples of cracks in on and around masonry fireplaces and a guide to their cause and remedy Masonry fireplace chimney & flue size requirements
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Typical standards require a cross-section area of the fireplace flue or chimney/vent to be equal to 1/10 of the area of the fireplace opening itself, for a conventional wood-burning installation and without considering the effects of a glass fire-door.
[Click to enlarge any image]
The FHA requires using a 1/8 ratio instead of 1/10 for chimneys that are less than 15 feet high and the 1/10 ratio for chimneys that are 15 feet or more tall. 
How do we measure fireplace chimney height?
Note that "chimney height" for the purpose of determining fireplace requirements, is measured not from the ground outside nor from the "floor" of the fireplace hearth.
Rather you should use the distance from the fireplace throat to the top of the chimney. Don't include the chimney cap in height measurements - that added distance does not develop draft in the flue.
Chimney Cross-Sectional Flue Shape Effects on Draft
At FLUE SIZE SPECIFICATIONS where we discuss chimney flue sizing for venting heating appliances such as boilers, furnaces and water heaters, we explain that in comparing two flues of exactly the same square inches of cross-sectional area, a round flue will have better draft than a rectangular one.
For this reason, fireplace and chimney guides offer a table of effective chimney vent area (measured as a cross-section of the flue opening) and flue sizes. You can find effective area and flue size tables in the Uniform Mechanical Code and in the MIA's Masonry Fireplace & Chimney Handbook and also in NFPA 211 - Standards for Chimneys & Fireplaces. 
Un-lined chimney flues are also specified as larger than lined installations and use the 1/8 ratio we explained above.
To use the fireplace chimney flue sizing table below, calculate the area in square inches of the cross section of the inside of the fireplace opening. For a rectangular fireplace opening just multiply its width by its height in inches to calculate the value to look for in column A of the table. The dimensions given in columns B & C of the chimney sizing table present standard clay chimney flue tile dimensions and shapes.
Adapted from Masonry Fireplace and Chimney Handbook, 2nd Ed., James E. Armhein, S.E., M.I.A. Masonry Institute of America, Los Angeles, CA 213-388-0472 prepared to include requirements of the 1994 UBC and other codes. - MIA.
Do not use a fireplace that is in any doubt about safety before it has been inspected by a professional.
Our photo (above) shows a fireplace mantel that collapsed and fell into the room. Smoke stains revealed on the brick might point to a chimney draft problem too.
The fireplace schematic (at left) shows the basic components of a masonry fireplace and their names. This drawing is obsolete in that it is missing a combustion air supply for the fireplace.
These articles on chimneys and chimney safety provide detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects.
tion methods and chimney repair methods are also discussed.
Carson Dunlop's sketch shows a cross section of the basic components of a chimney where a fireplace is installed. (Click the image at left or photos below to enlarge them).
Beginning with the outside inspection of the chimneys and structure, and continuing indoors, we check for a wide range of possible chimney hazards. Among these are issues surrounding chimney movement, settlement, or separation from the building.
Too often we discover that a building owner was aware that a chimney has moved, s/he has patched the gap between the chimney and the building, but s/he has not realized that the movement causes cracks and gaps inside the chimney or fireplace which are very dangerous.
Below we provide three photographs showing how a fireplace can become a fire hazard due to chimney settlement or inadequate support of the fireplace itself.
We start with a look at the fireplace hearth for evidence of movement.
In an easy-to-spot case of movement and separation between a fireplace hearth and the building floor take a look at the white caulk installed in an open crack between the hearth face and the floor in our photo (left).
A bit more investigating was needed to determine whether the floor was sagging away from a stable masonry fireplace and chimney or whether the chimney and entire firebox were leaning away from the building.
In the next case, just below, the gaps and cracks made it obvious that the chimney and fireplace were tipping away from the building in a dangerous condition.
First at above left we see a gap that has opened up between the fireplace floor and the hearth (above-left). Sparks may fall into this space, causing a building fire.
Second (above right) our photo shows a crack between the face of the fireplace and the fireplace box itself. We don't know without more analysis whether the brick facing has fallen away from a sound and safe fireplace or whether the fireplace has moved away from the facing.
Our third fireplace damage photograph (left) is the final nail in the coffin of this unfortunate fireplace.
A gap has opened in the fireplace below the chimney where the damper was cemented in place. There has been substantial movement of the fireplace itself (and probably the chimney too) - this is an unsafe fireplace that should not be used.
But not using the fireplace is not enough to be sure this home doesn't have another fire or glue gas hazard.
If a fireplace and chimney have settled and thus have become unsafe, we need to determine right away if any other building appliances such as a boiler, furnace, water heater, or woodstove are using other flues in the same chimney.
If the chimney has multiple users it is unsafe for all of them.
Also see these articles on chimney collapse hazards:
Some diagnosis of just what caused settling or movement in a hearth is critical.
A gap appearing between the hearth and the edge of the firebox might be due to inadequate hearth support - not such an ugly repair - or it might be due to settlement of the entire chimney and fire chamber away from the building - a major repair and a dangerous condition.
Our photo (left) shows a burned wooden floor in front of a fireplace hearth.
Hearth dimensions: A fireplace hearth should extend at least 16" (M.I.A.) past the front edge of the fireplace and at least 8" beyond each side of the fireplace opening.
Where the fireplace opening is 6 sq.ft. or bigger the front extension needs to be increased to at least 20" and the side extensions to at least 12" beyond the fireplace front.
The hearth for a masonry fireplace needs to be made of a brick, concrete, stone, or other (approved, listed) non-combustible material. The hearth slab needs to be at least 4" in thickness, it has to be supported by noncombustible materials or able to carry its own weight.
The "cribbing" or wood forms used to support a poured concrete hearth should be removed after construction is completed. We often find this wood material left in place - where sparks falling through a crack or gap can start a fire.
Carpets and other combustibles need to be kept away from the fireplace front and hearth.
Often where the hearth sits at floor level we find that someone has installed carpeting right up to the fireplace - a fire hazard as our client is remarking in our photo (above).
Stuffing a pillow into the chimney throat of a fireplace (above left) might slow the loss of warm air from a home, but it's a dangerous substitute for a missing or broken fireplace damper. What if someone lights a fire without noticing this stuffing?
A normal cast iron fireplace damper is shown in closed position in our photo at above right. Closing the damper when the fireplace is not in use will make a significant reduction in heat loss from most buildings. \
Inspect fireplaces for a working damper. Where a steel insert fireplace is installed, inspect the upper portions of the fireplace at the chimney throat with great care. A rusted-out steel fireplace inset will be unsafe, wont' work properly, and will be costly to replace.
Our photograph (left) shows a steel fireplace insert at an incomplete fireplace installation in a basement. What about that plywood "face" nailed around the steel fire chamber?
Continue reading at FIREPLACE INSERTS or select a topic from the More Reading links shown below.
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