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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” 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.

Flue Pipe Installation

Flue Pipe Installation.

The rules provided here are based on the CSA installation code used in Canada.

For installation requirements call the Barrie WETT Inspector at 705-795-8255



  1. Barrie Wett Inspections - Flue Pipe AssemblyMaximum overall length of straight pipe: 3 m (10 ft.)
  2. The assembly should be as short and direct as possible between the stove and chimney. The use of two 45 degree elbows is often preferable to a single 90 degree elbow because less turbulence is created in the exhaust flow and they result in less horizontal run.
  3. Maximum number of 90-degree elbows: 2. Maximum unsupported horizontal length: 1 m (3 feet).
  4. Galvanized flue pipes must not be used because the coatings vaporize at high temperatures and release dangerous gases. Use black painted flue pipes.
  5. 6-, 7-, and 8-inch diameter flue pipes must be at least 24 gauge in thickness.
  6. Flue pipe joints should overlap 30 mm (1 1/4 in.)
  7. Each joint in the assembly must be fastened with at least three screws.
  8. The assembly must have allowance for expansion: elbows in assemblies allow for expansion; straight assemblies should include an inspection wrap with one end unfastened, or a telescopic section.
  9. Minimum upward slope towards the chimney: 20 mm/m (1/4 in/ft.).
  10. One end of the assembly must be securely fastened to the flue collar with 3 sheet metal screws and the other end securely fastened to the chimney.
  11. There must be provision for cleaning of the pipes, either through a clean out or by removal of the pipe assembly. Removal of the assembly should not require that the stove be moved.
  12. The crimped ends (male) of the sections must be oriented towards the appliance so that falling dust and condensation stay inside the pipe.
  13. A flue pipe must never pass through a combustible floor or ceiling or through an attic, roof space, closet or concealed space.
  14. Minimum clearance from combustible material: 450 mm (18 in.). The minimum clearance may be reduced by 50 percent to 225 mm (9 in.) if suitable shielding is installed either on the pipe or on the combustible surface.

Single Wall Pipe AssemblyA straight up single wall flue pipe assembly.The ideal flue pipe assembly is one that rises straight up from the appliance flue collar and directly into the chimney with no elbows. The system at the right is single wall pipe with an inspection wrap (pipe coupler) to allow it to be assembled and disassembled without moving the stove.

A straight flue pipe assembly offers the least restriction to gas flow and results in stronger draft. Straight assemblies also need less maintenance because there are no corners for creosote deposits to accumulate.

A perfectly straight flue pipe assembly is another good reason to install chimneys up through the warm space of the house, instead of out and up and outside wall.

Certified double-wall flue pipe systems are also available. These systems are tested to determine the minimum clearance at which they can be installed. The clearance information is found on the labels attached to the pipe and in the manufacturer’s installation instructions. The rules for their installation may differ from the rules for single-wall flue pipes.

Double Wall Flue Pipe AssemblyA straight up double wall flue pipe assembly. This one is the sealed type.The minimum installation clearances for certified double-wall flue pipes are much less than those for single-wall pipes. Also, the maximum length of a double-wall flue pipe assembly may be greater than is permitted for a single-wall pipe.

There are two general types of double-wall flue pipes: sealed and vented. A sealed double-wall flue pipe is effective at retaining the heat in the flue gases because the air space between the inner liner and outer shell acts as an insulator.

A sealed double-wall pipe is a good choice to maximize draft and minimize creosote deposits. Use sealed double-wall pipes if the assembly must be long or if the appliance is expected to produce low flue gas temperatures. The system to the left uses a sealed double wall telescopic length between the stove and chimney.

A vented double-wall pipe allows cooling air to pass between the inner and outer layers. Where the flue pipe assembly is short and straight, a vented double-wall pipe can be acceptable. However, vented pipe is not a good choice for longer flue pipe assemblies or for appliances that are expected to produce low flue gas temperatures.


Contact the Barrie WETT Inspector

How to reduce Clearances to Combustibles

More information from Barrie WETT inspections

Wood Heating

Wood Heating - Barrie Wett InspectionsWood heating is practiced on a small scale, the fuel is usually harvested from a local resource, and the users gain a more complete understanding of their impacts on the environment than users of other energy sources. As environmentalists have suggested, these are some of the very features needed for economic and environmental sustainability. Families who heat their homes with wood responsibly should be recognized for their contribution to a reduction in greenhouse gas emissions and a sustainable energy future.

Wood stoves are free-standing space heating appliances. Used either as the principal source of heat for a home or to supplement conventional heating systems, wood stoves are the most popular form of wood heating equipment because of their relatively low cost and installation flexibility. There are two general categories of wood stoves based on differences in combustion technology, emission characteristics and efficiency: conventional wood stoves and advanced technology, EPA certified wood stoves.

Wood cooking stoves have a cook-top surface, a bake oven and sometimes a reservoir for domestic hot water. Cook stoves are not common in Canada, although a few models are still available for sale in specialty stores. Cook stoves are exempt under the EPA wood burning regulations because the numbers were considered small and their manufacturers testified that practical cooking features and low emission combustion technology are incompatible. Smoke emissions performance for cooking ranges is not available, but particulate emissions are probably similar to conventional wood stoves.

Certified WETT inspectors will specifically inspect components of all wood-burning appliances and fireplaces to determine if they were installed safely and in accordance with building and fire code requirements. WETT inspectors are required to complete a minimum of four days of formal training and declare a minimum of 80 weeks of related field experience before being certified.

The best way to start your fire is with newspaper and dry kindling. Never try to get a blaze roaring with gasoline, kerosene or charcoal starter – you will get more firepower than you bargained for. Remember to remove ashes from your stove or fireplace regularly and store them in a covered metal container in a safe area away from the side of your house. The sparks in hot ashes can easily start fires. It is important to keep all household items – such as; drapes, furniture, newspaper and books – away from the heat and the stray sparks of your wood stove or fireplace.

Any fuel you choose to heat your home will affect the environment. When wood is not burned properly, it can have negative impacts on both outdoor and indoor air quality. Smoldering, smoky fires that produce a plume of blue-grey smoke from the chimney are the main cause of air pollution related to wood burning. You can reduce the amount of smoke from wood heating in many ways.

The Barrie Home Inspector is a WETT Certified Professional Home Inspector for the Barrie, Alliston and Orillia area of Simcoe County. The experience and knowledge from over 4,000 inspections allows us to guarantee the best possible WETT and Home Inspection. The Barrie Home Inspector is also a Certified Building Code Official with the Ontario Building Officials Association.

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