Insulation is needed when the fluid in the pipe ________.

• A. Reaches dew point
• B. Freezes
• C. Boils
• D. Reaches ambient temperature

Answer: (A)

Condensation control is the key idea. Condensation happens on a surface when that surface’s temperature falls to, or below, the surrounding air’s dew point. If the fluid in the pipe cools the pipe surface enough and the room is humid, moisture will condense on the outside of the pipe. Insulation slows heat transfer between the pipe and the room, keeping the pipe surface warmer and above the dew point, which prevents condensation from forming. In humid climates, this becomes especially important, which is why insulation is used to keep the pipe from reaching the dew point.