Fireplace Construction and Safety

Ensuring your Fireplace meets or exceeds requirements of Ontario Building Code and CSA Standard B365-10 is the first step in enjoying the benefits of a wood burning fireplace without jeopardizing you and your families safety. Having a WETT Certified Inspector complete an inspection of your Fireplace is almost always required bby most insurance companies prior to issuing Home Insurance.

Masonry Chimney Construction

A masonry chimney is constructed of a variety of masonry and metal materials, including brick, mortar, concrete, concrete block, stone, flue tile, steel and cast iron. All masonry chimneys contain combinations of, or possibly all of, these materials, most of which are adversely affected by direct contact with water or water penetration.  When clay flue tiles are cracked or damaged by chimney fire they are typically replaced with a continuous Stainless Steel liner.  In some cases the clay flue liner has to be removed to install proper sized liner for appliance.

Most fireplaces are constructed of masonry with heatilator or fire brick in fire box area or they are a prefab fireplace which generally has a firebox of cast refractory panels, and usually some metal is trim around the firebox.  Most prefab fireplaces have an installation label specifying and clearance to combustible products.

Chimney Liners

Clay tiles are the most common type of masonry chimney liners.

• Advantages: They are inexpensive, readily available, and perform quite well for open fireplace chimneys that are properly maintained.
• Disadvantages:  They cannot rapidly absorb and evenly distribute heat during the rapid temperature rise that occurs during a chimney fire, causing the flue tiles to crack and split apart (see the video below). The second disadvantage is that tiles cannot adequately contain the liquid combustion byproducts produced by modern gas appliances.

A fireplace is a structure made of brick, stone or metal designed to contain a fire. Fireplaces are used for the relaxing ambiance they create and for heating a room. Modern fireplaces vary in heat efficiency, depending on the design.

Historically they were used for heating a dwelling, cooking, and heating water for laundry and domestic uses. A fire is contained in a firebox or fire pit; a chimney or other flue allows exhaust to escape. A fireplace may have the following: a foundation, a hearth, a firebox, a mantelpiece; a chimney crane (used in kitchen and laundry fireplaces), a grate, a lintel, a lintel bar,  mantel, a damper, a smoke chamber, a throat, a flue, and a chimney.

On older style fireplaces the exterior chimney often has a corbeled brick crown, in which the projecting courses of brick act as a drip course to keep rainwater from running down the exterior walls. A cap, hood, or shroud serves to keep rainwater out of the exterior of the chimney; rain in the chimney is a much greater problem in chimneys lined with impervious flue tiles or metal liners than with the traditional masonry chimney, which soaks up all but the most violent rain. Some chimneys have a spark arrestor incorporated into the crown or cap.

Fireplace Inspection Defects

Chimney leaks

Water leaks at the chimney cap or anywhere along its run, or even from ground-water entry in some cases, can lead to damage making the chimney unsafe. For a complete inspection of the entire run of the chimney it must be cleaned and chimney video camera are required, but often there are indirect clues of chimney leaks that show up as rust or moisture stains on the fireplace damper or in the fire box.

Lack of Combustion Air

All fireplaces must be provided with an outside air source for the combustion of fuel.  Fireplace Operation Most fireplaces burn wood as a solid fuel.  For proper operation, any fireplace must be provided with an adequate supply of oxygen and have the ability to exhaust a variety of combustion byproducts. Every fireplace must have a supply of combustion air from outside. The air intake should be located as close as possible to the opening of the fireplace. There are several reasons for this requirement. By providing the fireplace with an external source of combustion air the competition for inside air is reduced and therefore the potential for back drafting of the by-products of combustion is minimized.

Water Leaking into Fire Box

The most common source of water leaking into your chimney is typically the cap.  The chimney cap is the cement part on top of the chimney. The bricks go up around the tile flue liners, but at the top you need something to stop the rain and snow from just falling in around the tiles. The  purpose of the chimney cap is to keep rain and moisture out. Cracks in the chimney cap can occur from shifting of the structure or from shrinkage dating back to the first day the cap was installed. When your cap has cracks, the water goes right through those cracks and can cause considerable damage to exterior brick due to thawing and freezing cycles in the winter months.  Two signs of trouble are damage to exterior brick and water leaking into your fire box.

All modern masonry chimneys are required to have a one piece chimney cap or poured in place concrete cap as per Ontario Building Code. Excerpt below:

Ontario Building Code 9.21.4.6. Chimney Caps

(1) The top of a chimney shall have a waterproof cap of reinforced concrete, masonry or metal.
(2) The cap required in Sentence (1) shall slope from the lining and be provided with a drip not less than 25 mm from the chimney wall.
(3) Cast-in-place concrete caps shall be separated from the chimney liner by a bond break and be sealed at that location.
(4) Jointed precast concrete or masonry chimney caps shall have flashing installed beneath the cap extending from the liner to the drip edge.

Height of Chimney

In accordance with the Ontario Building Code 9.21.4.4. Height of Chimney Flues

(1) A chimney flue shall extend not less than,  (a) 900 mm above the highest point at which the chimney comes in contact with the roof, and (b) 600 mm above the highest roof surface or structure within 3 m of the chimney.  Note:  FB chimneys that extend over 5 feet from roof surface are required to have bracing installed.

Clearances to Combustible Material

The clearance of a fireplace to combustible framing must conform to Ontario Building Code requirements.  Interior wall framing must have 100 mm (4″) of clearance from a fireplace while exterior wall framing must have at least 50 mm (2″) clearance. The clearance from the smoke chamber to interior wall framing can be no less than 50 mm (2″) and 25 mm (1 “) to exterior wall framing.

Cleaning Your Chimney

A buildup of creosote is the main reason that it’s important to have your chimney cleaned and inspected annually.  The three distinct types of chimney deposits, tar, soot, and creosote are all byproducts of wood burning, and “creosote” is what the mix of the three components is usually called.  How to properly clean your chimney depends upon degree of creosote buildup on your flue lining.  Creosote in all of its forms is dangerous because it can highly combustible and is one of the main causes of chimney fires.

First degree creosote has a high percentage of soot and can be removed from a chimney with the use of chimney brush.  First degree creosote develops when there is a relatively good combustion of the wood and/or relatively high flue gas temperatures. The combination of lots of combustion air heats up the chimney and is common with open fireplaces.

2nd Degree creosote is typically a building up of shiny black flakes.  The most common cause of this build up is having fires with restricted air intake.  Lack of combustion air vent with glass doors or dampening down a fire to restrict fire wood consumption are primary causes of this type of creosote.

3rd Degree creosote looks like tar coating which will continue to build up in layers often requiring replacement of chimney liner.  This creosote buildup can be caused by excessive dampening, a cold chimney, flue is over sized and insufficient combustion air.

 

Fireplace Safety Tips

• Never burn garbage, Christmas wrappings or painted/treated wood, only dry fire wood
• Open damper fully before lighting a fire. ( preheating chimney by burning clean paper is advised )
• Keep the fire to the back of the fireplace – do not overload firebox with wood
• Always use a spark screen or glass doors – and ensure gaskets are in good condition
• Follow the manufacturers instructions when burning artificial logs
• The two primary threats caused by creosote are chimney obstruction and chimney fires. If a chimney is obstructed, the result can be that toxic gases, including carbon monoxide, can enter the home. Everyone with a fireplace or stove should have a carbon monoxide detector in the home, since the gas is odorless, invisible, and tasteless.

For more information on Fireplaces, Wood Stoves or Pellet Stoves or WETT Inspections contact Roger at:

705-795-8255 or 888-818-8608

Email Roger  roger@napoleon.cc