When reading installation instruction manuals for various furnaces, I see language that specifies that the vent or flue should terminate a certain distance above the “average snow level,” or “above the minimum snow level” on the roof. These instructions for how high to install the pipe above the roof often conflict with the InterNACHI standard of 3 feet. The point being that the installation instructions for furnace flues/vents have different standards than InterNACHI, and rarely say 3 feet.
Do installation instructions trump InterNACHI standards when doing a home inspection where the inspector has a contract saying that they follow InterNACHI Standards of Practice?
How do I measure the average snow accumulation on a roof? Is it the most snow that will accumulate on any given day?