What is the minimum inside diameter for the condensate and drain line?

What is the minimum inside diameter for the condensate and drain line?

• A. 1/2 inch ID
• B. 5/8 inch ID
• C. 3/4 inch ID
• D. 1 inch ID

Answer: (C)

Drainage capacity is the main idea here: the condensate line must carry away the water produced by the evaporator by gravity without backing up or clogging. The minimum inside diameter of 3/4 inch provides enough cross‑sectional area to handle typical condensate flows from most residential and light commercial systems while keeping the velocity high enough to reduce the chance of buildup and stagnation. Smaller sizes, like 1/2 inch, are more prone to clogging from mineral deposits or debris and can back up under higher humidity or longer runs. A size of 5/8 inch isn’t generally accepted as the minimum in most codes, and while 1 inch would work, the question asks for the smallest acceptable size, which is 3/4 inch.

Drainage capacity is the main idea here: the condensate line must carry away the water produced by the evaporator by gravity without backing up or clogging. The minimum inside diameter of 3/4 inch provides enough cross‑sectional area to handle typical condensate flows from most residential and light commercial systems while keeping the velocity high enough to reduce the chance of buildup and stagnation. Smaller sizes, like 1/2 inch, are more prone to clogging from mineral deposits or debris and can back up under higher humidity or longer runs. A size of 5/8 inch isn’t generally accepted as the minimum in most codes, and while 1 inch would work, the question asks for the smallest acceptable size, which is 3/4 inch.