Why does the furnace, water heater vent pipe require clearance to combustible materials?
Gas burning appliances vent pipes produce heat when discharging exhaust gases to exterior. Temperature of the vent pipe is transferred to the surrounding area and all the materials that are in the vent pipe vicinity. Problems start arising if those materials are combustible and located to close to the furnace, water heater vent pipe. If you apply heat to a combustible material for some period of time (that varies between materials), its point of ignition will gradually get lower and eventually little heat will be required to start a fire – that’s why you need a clearance between the vent pipe and a combustible material. Flash point / temperature at which wood will ignite is 572F (300C). For all of us not aware of this condition, here are the required / minimum furnace, water heater vent pipe clearances and locations where the single or double wall vent pipes can be installed. Furnace / water heater vent pipe clearance – single wall Minimum distance between the single wall vent pipe and
