PVC Outgassing: What's The Fuss?

Pipes have been made of many materials over the years including copper, iron, aluminum, clay, and even wood! Plastic, in the form of polyvinyl (PVC) pipe, is a relatively new addition to the mix. PVC pipe has been approved for use in both fresh and wastewater applications, and is also used in exhaust applications for high-efficiency furnaces.

Billions of pounds of PVC are made each year and home construction, repair and remodeling materials often contain PVC. A debate has arisen over the safety of PVC in homes, and that’s causing some people to rethink their use of PVC-containing materials.

A phenomenon known as “outgassing” is at the center of the concern over the use of PVC-containing materials. Outgassing refers to the release of volatile organic compounds (VOCs) from products that contain PVC. VOCs can be released from the PVC into the air or water and have been implicated in “sick building syndrome,” and other indoor air quality issues. Further, VOCs can be found in water that’s been carried through PVC pipe.

When heating is involved, the use of PVC requires some special considerations. High efficiency furnaces are designed to vent directly to the outdoors. They also take in fresh air from outside the home, rather than recirculating semi-heated air already inside. PVC is used in heating applications mainly because it’s inexpensive. It’s also able to stand up to the stress of repeated heating-cooling cycles.

The furnace exhaust, which contains the noxious by-products of combustion, is hot. (After all, it’s just come out of the furnace, right?) Heat tends to accelerate the release of VOCs, so when PVC is used as part of the furnace exhaust system, the amount of VOCs released into the outside air (and the inside air around the exhaust pipe) tend to increase.

Some homeowners who are concerned about PVC outgassing and its long-term health effects have begun looking for alternatives to PVC for their furnace exhaust ports. When a substitute for PVC is sought, we generally recommend stainless steel. Stainless steel is certainly more expensive than PVC but it’s inert so it won’t interact with the environment around it. It also tolerates the repeated heating-cooling cycles and moisture from the outside air (and dampness in basements) very well. Since stainless steel is durable, it will also generally last the lifetime of the furnace.

If you have a high-efficiency furnace and are concerned about PVC outgassing, or would like to look at alternatives to PVC for other applications (like plumbing), please give us a call at Boston Standard Plumbing & Heating at (617) 288-2911 for a consultation. We’ll be happy to suggest alternative plumbing, heating and cooling materials.