The Concerns Of Cellular Core Piping On Exhaust Systems

Date Published: October 25, 2017

PVC or ABS plastic piping is often used on high-efficiency heating and water heating systems as vent piping for the exhaust gases, since the exhaust temperatures are relatively low.  This piping is often vented out the side of the home.

There are different types of piping used, and one style commonly used is called ‘Cellular-Core” PVC.  This type of piping differs from solid PVC or ABS as it has a core built into the walls of the pipe. This makes the piping cheaper and lighter, but slightly less rigid than it’s solid counterpart.  Recently, municipalities and many material manufacturers are no longer allowing cellular core piping (PVC and ABS) for new installations on exhaust ventilation applications due to concerns that have developed in certain installations.

The issue arises with the piping when it is used as an exhaust vent for mechanical items. This includes high-efficiency furnaces, boilers, and water heaters. The higher temperatures of the exhaust can distort the interior core of the piping and fittings which can cause holes or cracking after prolonged exposure. Cracking or warping of exhaust pipes can lead to a larger safety issue where an appliance could vent carbon monoxide into the living area of a home.  For this reason, some municipalities are not allowing Cellular Core PVC or ABS to be used for venting applications.

Image of Cellular Core Piping

Have concerns with cellular core piping or other aspects of your home? Learn more about our inspection services here

Is There Code Requirements Against Exhaust Related Cellular Core Piping Installations?

Currently, there is not a requirement that prevents cellular core piping from being used. That is currently left up to the manufacturer’s installation guidelines on a per appliances bases. However, some cities like Loveland, CO have enacted a policy that prohibits the use of cellular core piping on exhaust lines. The following statement is an excerpt from the Loveland Policy and Procedure Statement BDP-16-01:

ISSUE: Information from product listing agencies, product manufacturer’s, and a licensed plumbing engineer serving as committee chair for the International Code Council’s Residential Plumbing and Mechanical Committee has demonstrated that the use of cellular core PVC piping for exhaust vent piping is not compliant with the requirements of the International Residential Code, has been reported to have failed and caused life-threatening conditions, and has been specifically warned against by the major manufacturers of such pipe, warranting the prohibition of the use of such pipe for vent piping on fuel-fired combustion appliances.

EVIDENCE: The CSA, a world recognized and code approved product testing and listing agency recently provided guidance concerning the use of cellular core PVC piping for venting of fuel-fired combustion appliances stating that “the use of [cell core vent pipe] as a vent pipe for combustion products is no longer permitted in the US and Canada.

There have been reported instances of this material failing in the field and releasing carbon monoxide into the living space…At this point all manufacturers of these products should have amended their instruction manuals to reflect this change.”

The Supplemental Information to the installation instructions for one of the largest manufacturers of cell core PVC piping, Charlotte Pipe, states “Never use PVC or ABS cellular core pipe for combustion gas venting”. Information from other pipe manufacturers provides similar directives.

The Chairman of the ICC’s Residential Plumbing and Mechanical Committee indicates states that there is no listing or testing of cellular core piping for use as combustion vent piping and he attributes the death of a family of four in Aspen in 2008 to carbon monoxide poisoning occurring as a result of failed cellular core PVC combustion vent piping.

He further states that requirements within the codes that products, including cellular core PVC vent piping, be tested, listed and labeled for their intended use, have not been met by this product. He also states that he has personally witnessed failures and degradation of this product in the field when used in this manner.

You can read the City of Loveland full policy document here.

So What Should You Be Doing Now?

It is very easy to know if your furnace, water heater or boiler is using this type of piping. You can view the exhaust pipes near the appliance, and see if the words “cellular core” is labeled on the side wall.

If so, consider having the affected piping evaluated, or replaced in the future by a qualified HVAC contractor. At a minimum, consider installing an additional CO detector in the mechanical room or near the affected piping to alert you to any flue gas concerns that may develop as the piping ages. Consult with an HVAC contractor for more details.

At Scott Home Inspection, we are always on the lookout for this style of piping during our inspections. When the issue became more known in the industry and the City of Loveland made their announcement, we revised our inspection checklist to include visually inspecting the furnace, water heater and boiler exhaust piping for the presence of Cellular-Core piping.

If present, we add a comment to our inspection report advising the client to have the piping inspected by an HVAC contractor, and at minimum add another CO detector in this location.   If you have further questions about this topic, don’t hesitate to write a comment below. If this issue is affecting your home or if you found this article informative, please share it so others can be aware of this concern.

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About the Author: Chris Scott

Chris Scott is an ASHI certified home inspector with multiple years of experience in home inspections, blower door testing, duct leakage testing, and Boulder Rental License Inspections. Chris is also the Website Coordinator for Scott Home Inspection.

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    Michael Liu November 19, 2019 at 3:44 pm

    I will be installing a power-vent water heater. I had intended to use 3″ ABS for the venting due to ABS’s higher temperature rating compared to PVC. But almost all commonly available ABS pipe is cellular core. Large diameter Sch40 CPVC is difficult to obtain locally and is prohibitively expensive. So that leaves me with 3″ Sch40 solid core PVC. Any problems?

    • George Scott November 19, 2019 at 5:17 pm

      Using solid-core is the key. Regarding the diameter, that’s something you should check with the equipment installation guidelines to see what size piping they require.

        Michael Liu November 19, 2019 at 5:57 pm

        Yes, I should have mentioned that the water heater is spec’d for either 3″ vent (for a maximum equivalent vent length of 50′) or 4″ vent (for a maximum equivalent vent length of 100′). My installation will have an equivalent vent length of 20′ (10 feet of straight pipe + two 1/4 bend long-sweep elbows).

    Don C March 18, 2018 at 7:39 am

    I agree with Brian . I am a home owner going to install radon venting . Looking at the specs on Menards cellular pipe is listed as drain waste only with 0 working pressure . Just can’t believe that it would be used for heating . Thanks for this post .

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