Thermal expansion code in Mecklenburg County NC

[Bruce A. King]

I talked with the chief inspector for quite awhile yesterday to get a clarification on Mecklenburg's position on the thermal expansion code AND their letter of interpretation since opinions are all over the place on this. He was very experienced and helpful.



Here is what I noted from the information on the phone call:

(note, you must understand the difference between a PRV, a PRV with a thermal bypass feature, an anti-backflow and a true thermal bypass device to understand all of this)


1. A thermal expansion device is not required by the code on single family homes if no anti-backflow device is present.


2. A PRV with a simple thermal bypass feature is allowed since it is not considered an anti-backflow device even though the street pressure could someday exceed a safe pressure and prevent the thermal bypass from reducing the house pressure. This is usually the one we see installed.


3. If the building inspector does not find a need for a PRV the day of the inspection, the house is not even required to have one installed. Future conditions are not a concern of the code.


4. If a house is found to need a PRV, it must be located next to the water meter in order to meet code and to protect the line to the house.


5. Multi-family, condo's and some townhomes do require a dedicated thermal expansion device since they have anti-back flow valves installed.


6. The plumbers are leaving the box/packaging on site for the building inspectors to verify which type PRV is installed.


Here is the link to their interpretation that was written by someone in Raleigh:

http://www.charmeck.org/NR/rdonlyres...ionControl.pdf

I will still report this as a needed upgrade since the street pressure can exceed a safe pressure for the house at some point in the future.