Updated: Apr 12, 2020
Just check out that picture from a recent inspection off of Summit Road in the Santa Cruz mountains! According to the National Fire Protection Association, heating equipment was responsible for over 50,000 structure fires in 2017. It is certainly not a surprise, considering how cavalier some people are about the space surrounding their furnaces and water heaters vents. I imagine they don’t realize the dangers in using those areas for storage or allowing wood to be too close. Just try touching one of those vents when your water heater or furnace is operating and you will see just what I mean! Careful, don’t get burned!
Combustible materials such as wood are subject to pyrolysis, which is the decomposition of materials that are exposed to heat over time. Pyrolysis will lower a material’s flammability point, meaning that something like a cardboard box that has degraded through pyrolysis will catch fire at lower temperature than before it had been subjected to heat.
Up in attics, concerns regarding pyrolysis are especially a concern where the furnace or water heater vent penetrates the roof. Type B vents that are commonly used on furnaces and water heaters should have a 1 inch clearance between the vent and the wood roofing components, specifically the plywood or OSB sheathing. I have seen many instances where the vent is in direct contact with that wood. A fire just waiting to start. Trimming that wood a bit would be a really, really smart idea!
So the next time you have your furnace or water heater on full bore, just give that vent a quick pat with your finger, and you will see what I mean!
See you soon -