What are the three types of approved copper piping for gas installations?

For gas installations, the three types of approved copper piping are indeed Types L, K, and ACR.

Type L copper pipe is commonly used for its strength and durability, making it suitable for gas applications where pressure resistance is necessary. It's thicker than Type M, which provides greater protection against damage. Type K is even thicker and often used where higher pressure capabilities are needed, and its superior wall thickness makes it ideal for underground applications. ACR (Air Conditioning and Refrigeration) copper tubing is designed for HVAC applications, but it’s also suitable for gas installations due to its seamless construction and resistance to corrosion.

The inclusion of Types L and K in the correct answer underscores their usage in both gas transport and general plumbing. Although other types of copper piping exist, not all are approved for gas installations due to concerns about pressure ratings, potential for leaks, and material properties relevant to gas transport.