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Reducing Clearances

Reducing Clearances

Air-Cooled Radiation Shields Clearances are designed to keep combustible materials around a wood burning appliance below 90°C (190°F), even during a chimney fire. It is possible to build an air-cooled radiation shield, which can reduce clearances because moving air is a very effective cooler.

When radiation from an appliance hits a shield and heats it, the shield in turn heats the air behind it. Since hot air rises, the air moves up and exits through spaces at the top of the shield, andWETT Clearance Chart cooler air is drawn in at the bottom of the shield to replace it. The hotter the shield gets, the faster the heated air rises, and the more air passes by the shield, cooling it down.

A shielding system made of small sheet metal panels is less likely to buckle than one made of a single large sheet. The edges of the metal should be hemmed to improve its strength and appearance. This kind of system is inexpensive and easily adapted to many situations.

Wall shields must extend at least 450 mm (18 “) beyond each edge of the appliance and 500 mm (20”) above the appliance. To allow air to flow behind the shield, there must be a space of at least 25 mm (1 in.) at the bottom of the shield and a 21 mm (7/8 in.) space between the shield and the wall. (If the shield must extend up the wall to shield the flue pipe, a 75 mm (3 in.) space must be left at the top so the cooling air can escape).) The shield should be permanently mounted on the wall using screws through non-combustible spacers.

Shield Construction Rules

  1. Minimum space between shield and combustibles: 21 mm (7/8 in.).
  2. Minimum clearance along the bottom of shield: 25 mm (1 in.).
  3. Maximum clearance along the bottom of shield: 75 mm (3 in.).
  4. Minimum clearance along the top of shield at ceiling: 75 mm (3 in.).
  5. Shield extension beyond each side of appliance: 450 mm (18 in.).
  6. Shield extension above appliance: 500 mm (20 in.).
  7. Edge clearance for ceiling shields: 75 mm (3 in.).
  8. Adhesives used in shield construction must not ignite or lose adhesive qualities at temperatures likely to be encountered.
  9. Mounting hardware must allow full vertical ventilation.
  10. Mounting hardware must not be located closer than 200 mm (8 in.) from the vertical centre line of the appliance.
  11. Mounting hardware which extends from the shield surface into combustibles may be used only at the lateral extremities of the shield.

Air-cooled shields for ceilings should have a 75 mm (3 in.) clearance from adjacent walls.

Certified Commercial Shields

If you do not want to build an air-cooled radiation shield, several different styles of metal and brick or stone commercial shields are available. Be sure that any commercial shield you buy has been certified and labeled by one of the three recognized testing agencies. The manufacturer’s instructions will specify how to install the shields, and the clearance reductions that can be achieved.

What Can Shields Be Made Of?

  •  Sheet metal with a minimum thickness of 0.33 mm (0.013 in.). This is only 30 gauge -26 gauge is better. The edges should be hemmed (safety edge). WETT Clearances
  • A solid brick wall at least 21 mm (7/8 in.) away from the wall and vented at the top and bottom.
  • Brick or tile slices mounted on an approved non-combustible board with a 21 mm (7/8 in.) air space behind it.
  • A certified commercial shielding system.

Note:  If a brick wall is built against a drywall or other form of combustible wall.  The measurement for clearance is taken from appliance to combustible wall.  You would consider the brick not to be there when determining distance.  That is why it is important to know the requirements before constructing heat shields to ensure that they will comply with WETT Inspection.

The first step in reducing clearances is to determine the minimum clearance, either from the appliance label or from the table of clearances for uncertified appliances. Then, calculate the permissible clearance reduction for the type of shield you plan to use from the table on clearance reduction. The channel spacers shown are the most effective type to use because they give good support to the shield and do not transmit heat through the mounting hardware to the combustible wall. Metal wall strapping, available from most building supply stores, is made of light steel channels that work well as shield spacers. Note that the bottom of the channel is notched to allow cool air to enter. The shield must extend 450 mm (18 in.) beyond each edge of the appliance and 500 mm (20 in.) above the top of the appliance.

Floor Protection

The floor pad must be made of a durable, noncombustible material, such as sheet metal, grouted ceramic tile, or mortared brick. Floor pads must normally extend not less than 450 mm (18 in.) in front of the loading door and 200 mm (8 in.) beyond the other sides and back. Floor pads must not be installed on carpet unless the pad is structurally supported so that it does not move or distort.  Most Fireplace shops now carry prefabricated ULC approved floor pads which can be easily placed in front of inspection.com/tag/fireplace/” title=”View all articles about fireplace here”>fireplace is hearth is not the required size.

Floor Pad Size

The floor pad protects flooring from hot embers that might fall from the appliance during fuel loading or servicing. The pad should extend at least 200 mm (8 in.) beyond the sides and rear and 450 mm (18 in.) in front of the loading door. The floor pad must be a continuous, non-combustible surface. The floor pad must not rest on the carpet unless it is strong enough to resist bending or cracking. The best floor pads are laid on the sub-floor so that their finished level is flush to the floor, so there is no edge to trip on.

If you are installing your own wood stove or fireplace insert you can call Roger at 705-795-8255 for requirements prior to doing work.

Fireplace Construction

WETT Inspections in Alliston has provided some of the information available in the Ontario Building Code regarding Fireplaces.   This information is provided just to indicate the type of regulations that apply to different wood burning appliances and should not be used as an installation guide.  If you require specific information about your wood burning appliance call the Alliston WETT Inspector at 705-795-8255 for current WETT requirements.

Combustion AirCOMBUSTION_AIR

OBC 9.22.1.4  (1)  Every solid fuel-fired fireplace, including factory-built fireplace, shall have a supply of combustion air from outdoors, etc.

Hearth Extension

(1) Except as required in Sentence (2), fireplaces shall have a noncombustible hearth extending not less than 400 mm (15 3/4 in) in front of the fireplace opening measured from the
facing, and not less than 200 mm (7 7/8 in) beyond each side of the fireplace opening.

(2) Where the fire chamber floor is elevated more than 150 mm (5 7/8 in) above the hearth, the dimension of the hearth measured perpendicular to the plane of the fireplace opening shall be increased by not less than
(a) 50 mm (2 in) for an elevation above 150 mm (5 7/8 in) and not more than 300 mm
(11 3/4 in), and
(b) an additional 25 mm (1 in) for every 50 mm in elevation above 300 mm (11 3/4 in).

Sample Fireplace ClearancesClearance to Fireplace Opening

(1) Combustible material shall not be placed on or near the face of a fireplace within 150 mm (5 7/8 in) of the fireplace opening, except that where the combustible material projects more than 38 mm (1 1/2 in) out from the face of the fireplace above the opening, such material shall be at least 300 mm (11 3/4 in) above the top of the opening.

9.22.5.2. Support of Hearth

(1) Except as permitted in Sentence (2), the fire chamber floor and hearth shall be supported on a reinforced concrete slab not less than a 100 mm (4 in) thick at its supports and, if
cantilevered, not less than 50 mm (2 in) thick at its unsupported edge.
(2) A hearth for a fireplace with an opening raised not less than 200 mm (7 7/8 in) from a combustible floor is permitted to be supported on that floor provided the requirements of Clauses 5.3.6.5. to 5.3.6.7. of CAN/CSA-A405-M, “Design and Construction of Masonry Chimneys and Fireplaces” are followed.

9.22.2.3. Steel Liners

(1) Steel liners for fireplaces shall conform to CAN/ULC-S639M, “Standard for Steel Liner Assemblies for Solid-Fuel Burning Masonry Fireplaces”, and shall be installed in accordance
with the installation instructions in that Standard.

Wood Fireplace:
These require a non-combustible hearth extension. Below are non-combustible materials and the required thickness that meets the specs.(min. R value of 1.16) for the fireplaces non-combustible hearth extension.

Required Damper and Size

(1) The throat of every fireplace shall be equipped with a metal damper sufficiently large to
cover the full area of the throat opening.

Hearth Extension Insulation Alternatives, R Value = 1.16

Hearth & Home HX3, HX4 – 1/2 inch
USG Micore 300 – 1/2 inch
USG Durockâ„¢ Cement Board – 2-1/4 inches
Cement Mortar – 5-7/8 inches
Common Brick – 5-7/8 inches
Ceramic Tile – 14-5/8 inches
Marble – 16-5/8 in. to 23-3/8 in.

These are the materials that can separate combustible material, lets say the wood flooring or wood framed hearth extension from the fireplace hearth.

Read more articles on WETT Inspection requirements

Orillia WETT Inspection

Do you require a basic visual inspection such as for insurance or pre-purchase of a home equipped with a wood burning appliance or fireplace? A basic visual inspection is a general overview of the readily accessible parts to determine if the system meets current regulations. We provide Certified WETT inspections on your fireplace, wood stove or pellet stove.

With over 10 years experience as a WETT Certified Inspector we can provide your “Site Basic” inspection that most insurance companies now require.  If you include your WETT Inspection as part of our home inspection package the fee is only $50.00 appliance.

What’s in a WETT Inspection?

When performing a  WETT inspection there are a number of areas that your trained inspector will inspect. Items such as the chimney, the liner, the smoke chamber, damper, firebox and other working parts inside the fireplace or woodstove to make sure that they are working properly. The inspector will also make sure clearances to combustible materials are within guidelines  so you can use your wood burning appliance safely.

How to Become WETT Certified?

There are a number of steps an individual has to complete on the path to obtaining WETT Certification.  Candidates  first have to pass a code compliance course to gain the required Wood Energy Technical Training for Barrie, Alliston or Orilliaknowledge concerning various code regulations for wood burning appliances.. Then they can choose to become a certified tech or advisor, earn their certification in chimney sweeping, or earn a WETT certification in SITE basic. Inspectors only become certified after at least 80 weeks of work in the field and require a letter of reference. Inspectors who choose to become WETT certified in SITE basic also have to complete 30 inspections of wood burning appliances, which further ensures that they have the necessary knowledge.

The majority of insurance companies now require any wood burning appliance,  wood stove, pellet stoves or fireplaces, to be inspected by a WETT Certified Inspector.

Areas required to be  inspected are:

  • Chimney
  • Liner / Flue
  • Smoke  Chamber
  • Damper
  • Firebox
  • Hearth / Floor Protection
  • Clearance to Combustible Surfaces

Ensuring the proper installation and operation of wood burning appliances is important for the safety of your families home.  Improper installation could cause a over heating or fire condition which could be life threatening if not detected in time.  We inspect your wood burning appliance and provide a WETT Inspection report at the time of the inspection.

Some things you can check yourself to see if your heater/chimney will pass inspection:

  • Appliances need to be certified by CSA, OTL, ULC or Warnock Hersey, to a current standard. If your stove is certified it will have a plate or sticker, usually on the back of the stove, that will tell you if the unit is certified, and which lab certified it. If the appliance has been modified or the label is not attached, it is no longer certified.
  • In mobile homes, appliances need to be specially certified for mobile home installation and have direct combustion air installed. The stove’s  instruction manual may list other requirements.
  • Existing Stainless chimneys must be listed to ULC S629, be installed according to the Manufacturer’s Certified Instructions and be of all the same brand. (tested and certified as a complete system). If there is no manufacturer’s sticker on any of the chimney components an inspector may not be able to pass it.
  • Quite often a masonry chimney will not have adequate clearance to combustibles. If the masonry chimney is inside the house there must be a 2” clearance, ½” if the chimney is partly or completely outside the building. Combustibles include framing, floor joists, floors, ceilings, paneling, etc. Also the chimney must extend right to the ground. If the masonry is resting on any sort of wooden support (called a bracket chimney) it will fail.

If you are unsure of any of your units requirements, please call Roger for a FREE CONSULTATION at 705-795-8255

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