Installing a new water heater or furnace can be tricky for the novice HVAC technician. There are many checks that need to be done and codes that need to be followed. While not being complete with the internals can lead to a harmful situation, one of the most important decisions that you will have to make is what material you should make the flue out of. Most furnace flues are made out of a metal material which is a proper decision do the high temperatures released through the flue during the use of the furnace. Due to the cost of metal, some technicians have chosen to use PVC pipe as material for furnace flues as a less expensive alternative.
Polyvinyl Chloride, otherwise known as PVC is a hard plastic pipe typically used in plumbing applications. Polyvinyl Chloride Pipe is the third most widely produced plastic in the world behind only polyethylene and polypropylene. Wikipedia quotes that PVC is "cheaper and stronger than more traditional alternatives such as copper or ductile iron. It can be made softer and more flexible by the addition of plasticizes, the widely used Phthlates. In this form, it is used in clothing , upholstery, and electrical insulation."
After inspections of commercial and residential installations, Inspectors have discovered that using PVC pipe can lead to destructive and possibly harmful conditions. It was noted that if the water heater scales up due to minerals in the water supply, it can cause the flue gas temperatures to rise which can lead to the fittings and pipe melting. Melting of the PVC pipe can be very dangerous. If behind a wall or in the ceiling, a melted pipe can leak condensation and create mold growth behind drywall. Even more dangerous is the release of carbon monoxide gas out of a melted pipe. Carbon Monoxide is a lethal gas and can lead to a fatal situation.
Manufacturers sometimes recommend using PVC for their installations. Research has found that...