Commonly a chimney is described as a vertical structure incorporated into a building and enclosing a flue or flues that extends above the roof and carries smoke and/or fumes to the exterior. Defective chimneys are the cause of most failed WETT Inspections.
Common Types of Chimneys
The masonry chimney is probably the most common form of chimney that I have inspected in the past ten years. Many older homes had one or multiple masonry chimneys installed. The problem with masonry chimneys is water penetration. All masonry chimney materials, except stone, will suffer premature deterioration as a result of extended contact with water. Masonry materials deteriorate rapidly when exposed to the freeze/thaw process, in which moisture that has penetrated the materials periodically freezes and expands causing damage. Water in the chimney also causes rust in steel and cast iron, weakening or destroying the metal parts. In Ontario you are required to use a one piece concrete cap with drip edge rather than old style mortar caps which were the cause of most water related problems. Adding a rain cap to your chimney can also greatly extend life of masonry and metal products.
Chimney Liners can consist of clay, ceramic or metal vent installed inside your chimney and are designed to keep products of combustion contained and directed to the exterior of building. The liner has three main functions, which are:
(1) The liner protects the house components from heat transfer, protecting combustibles.
(2) The liner protects masonry components from corrosive products of combustion.
(3) Liners provide the optimum flue for efficiency of fireplace or wood stove.
Clay tiles are the most common types of liner found in masonry chimneys. Clay liners are susceptible to cracking from heat or water intrusion and must be repaired prior to using chimney.
Cast in Place liners are light weight, castable, cement like product that provide a smooth, seamless passage for products of combustion in your chimney.
Metal Chimney Liners are the most common type of addition to aging or damaged masonry chimneys. For wood burning stainless steel liners are required and must be installed in accordance with manufactures instructions. Liner systems are tested and rated by UL or ULC and may not be modified beyond scope of installation instructions.
Chimneys and your homes Neutral Pressure Plane
Homes that have been renovated or newly constructed are made more airtight. This prevents makeup air from entering the home. This is common described as, “hot air rises”, and so does the warm air in your home.
When the warm air rises to the upper areas it’s creates a stack effect. That trapped air creates a pressurized area and forces its way out – through even very small openings such as recessed light fixtures and window frames. At the same time replacement air is trying to enter in the lower part of the building to make up for the escaping air.
Somewhere in your house is an area called the Neutral Pressure Plane (NPP). Above this theoretical plane, the air pressure is slightly positive compared to the outdoor air pressure and is trying to force its way out of the house. Below the plane, it is slightly negative and the house is trying to draw air in. The location of the NPP can constantly change in response to changing tempertures and openings in your home.
All of the factors that affect airflow in the house also influence the level of the Neutral Pressure Plane. Some affects are using dryers, cooking exhaust fans and bathroom fans.
Anytime a fireplace or fuel-fired heating appliance (except direct vent) is below the plane, air will tend to flow into the house through the chimney or vent. A common example of this is found in homes with two fireplaces, one below the other. As the upper level fireplace uses air for combustion and chimney flow, it depressurizes that level slightly causing air to flow upwards from the lower level. Since the lower level fireplace is below the NPP, it draws air into the basement through the chimney. Unfortunately, since those two flues generally exit the chimney close to each other, the makeup air can contain some smoke from the fireplace above and it can pick up unpleasant chimney odors as it passes down the chimney flue.
Call the Alliston WETT Inspection service for your Fireplace, Wood Stove or Pellet Stove certified inspection. WETT Certified for over 15 years. Call Roger at 705-795-8255
When buying a home with a wood stove, pellet stove or fireplace you can receive a $75.00 WETT Inspection in Alliston as part of home inspection package.