Wood Burning for Home Inspectors
The presentation covers wood fire science and what causes wood fires in homes, the importance of clearances, and what an inspector should know when performing a home inspection at a building that has a wood-burning appliance or fireplace.
Standards that apply:
- Masonry – fireplaces and chimneys
- Factory-built chimneys – determined by manufacturing codes
- Wood burning appliances and flue pipe assemblies – determined by manufacturing codes
- You need to tell your customers about any safety issues.
Science of fire and clearances:
- Pyrolysis – thermochemical decomposition of an organic material (in our case, wood)
- For a fire to happen, there needs to be oxygen, fuel, and heat.
- Just one little ember can start a chimney fire because of the soot and tar build-up.
- The build-up of soot and tar comes from the wood.
- Wood is comprised of cells trapped with water. When we cut down a tree for firewood, that wood has cells that contain water.
- In order to use that wood, we need to remove the water from the cells – it’s called “drying.” The reason we want to remove the water because the wood will tend to shrink and crack. We want all of that over with when we build a building.
- Similarly, when we cut wood down for firewood, we want to remove the water.
- Green wood is wood that has been cut down without drying. When we burn green wood, a few things happen – the water that’s in the wood needs to be evaporated out of the wood for it to burn. Plus, when you burn green wood, you will develop soot and tar build up in a chimney.
- Heat is transferred in three different ways:
- Interior chimneys need two inches of clearance.
- Exterior chimneys need half an inch. An exterior chimney has one surface exposed to the outside atmosphere or unheated space over the majority of its length.
- If you’re unsure if it’s an interior or exterior chimney, then call it an interior one to be on the safe side.
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