Information About Your Chimney

Your appliances chimney is probably the most important part of your wood burning system, more important than your appliance! Even a properly designed and properly installed appliance will not work properly or be safe if it is connected to an unsuitable chimney.

The ENGINE that drives the SYSTEM

Your appliances chimney is what drives your wood heating system. Hot flue gases from the fire rise up the chimney, creating draft. Your chimneys Draft is what draws air through the appliance and creates a good burning fire.

GOOD CHIMNEY RESULTS

A well built chimney produces draft immediately. It doesn’t have to be coaxed. An appliance connected to a good chimney lights and heats up quickly. It doesn’t spill out smoke when the door is opened. A well built chimney has few creosote deposits, and is less susceptible to chimney fires. Condensation typically will not be an issue in a well constructed chimney.

WHAT MAKES A CHIMNEY WORK PROPERLY

It’s similar in size to the appliance flue collar, so gases from the appliance flow quickly.
It’s insulated, so the gases stay hot and don’t condense and form creosote.
The chimney is located inside the house to keep it warm, reducing build up of condensation and creosote, and prevents draft reversal.

Many people assume an exterior chimney is safer in the event of a chimney fire. This is not true. Inside is better! In fact, there is much less chance of having a chimney fire if the chimney is located inside the house. When deciding to install an exterior chimney, consider having a “chase” built around it to protect it from wind and cold.

Types of Chimneys

Conventional Masonry Chimneys

Masonry brick chimneys have been utilized for many years. Most masonry chimneys built since the 1950’s are lined with
flue liners of clay or other materials, which improve the durability and performance of the chimney. If you have an older unlined masonry chimney and want to use it to vent a wood burning appliance, it must be lined, to ensure that the chimney is similar in size to the appliance flue collar.

RELINING A MASONRY CHIMNEY
If you have an unlined masonry chimney, check with a WETT certified inspector to find out if it should be lined. If it’s already lined, check the condition of the liner. If it’s cracked or broken, or if it’s the wrong size for your wood burning appliance,
it will need to be replaced by a suitable liner.

Type “A” Chimneys ( not permitted )

Type A metal chimneys became popular in the 1950’s. They were designed primarily for use with oil furnaces, but ended up being used for wood burning appliances as well. Type A chimneys cannot withstand severe chimney fires without damage. They are not suitable chimneys for wood burning appliances. Since 1983, chimneys specifically designed for use with wood-fired appliances have been required.

650ºC Metal Chimneys

In 1981, a new standard for factory-built chimneys was created. This standard requires factory built chimneys to be
tested at a continuous flue gas temperature of 650°C (1200°F).  By 1983, this standard had been incorporated into most
building codes. A modified version of the 650°C standard is used to test chimneys for factory-built fireplaces.
The so-called 650°C chimneys are much safer than the old Type “A” chimneys. They use more durable stainless steel liners than Type “A” chimneys, and are better insulated. Consequently, they can safely contain the temperatures common in a chimney fire. Since 650°C chimneys are better insulated, creosote tends not to build up as readily, so chimney fires are much less likely.

Chimney Termination Requirements

The top of a chimney must be at least 900 mm (3 ft.) above the point where it contacts the roof. It must also be 600 mm (2 ft.) above any roof surface or structure within a horizontal distance of 3 m (10 ft.). Metal chimneys need a cap to keep water out of the space between the inner liner and the outer shell.

Measure from the edge of the chimney flue closest to the roof, horizontally, until you touch the roof surface to check the ten-foot clearance rule distance.

Check the chimney top for damaged masonry (or rusted metal), a missing cap, damaged, cracked, or missing top seal or crown on the top of a masonry flue, and here, an important discovery (at least in some jurisdictions) is whether or not the chimney is single wythe or thicker masonry and whether or not the chimney has (or perhaps needs) a chimney liner.