HVAC Piping Identification

HVAC Pipe Measurements

• Plumbing pipes are measured to exclude the pipe itself in the diameter, but HVAC pipes include the pipe in the diameter. A plumbing pipe labeled as 1/2 inch will measure 5/8 inch from the outside, but a 1/2-inch HVAC copper pipe will be smaller because it is 1/2 inch wide on its diameter, including the pipe.

Fuel Pipes

• The pipes used to carry gas, propane or oil into your home for furnaces or boilers are easy to identify. Gas pipes, if made from copper, should have the word "Gas" written on the pipe along every 6 feet of pipe length. If you do not see the word, look for a pipe painted yellow or with a yellow stripe along its length to identify it as a gas line. Steel and cast iron are the most common pipes for carrying gas.

Air Conditioning Pipes

• The pipes in your air conditioner circulate a refrigerant through the system. These are usually copper, but air conditioner copper pipes are not the same as water pipes for your plumbing system. Air conditioning copper pipes will be of ACR grade, indicating that they are air conditioning/refrigeration pipes.

Hydronic System Pipes

• Hydronic systems use a boiler to generate steam or produce hot water to flow through pipes that feed radiators or convectors. These might be one-pipe steam systems that carry steam to the radiator and bring the condensed water back through the same pipe. Some systems are two-pipe systems that pass hot water through a convector with one pipe and return it to the boiler with a second pipe. Pipes for hydronic systems can be made of copper, steel or cross-linked polyethylene. If your hydronic system pipes are not marked, turn on the heat and wait for the system to heat up. Use a laser thermometer to gauge the temperature of the pipe in question. If it is a hydronic pipe, it will be hotter than the pipes surrounding it.