The condensate and drain line size is specified in terms of inside diameter. Which option correctly states the required size?

The condensate and drain line size is specified in terms of inside diameter. Which option correctly states the required size?

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

Answer: (B)

The key idea is that drain lines are sized by inside diameter because that is the actual passage the condensate travels through. The required size is three-quarters of an inch inside diameter. Using inside diameter reflects the true flow capacity and matches the standard fittings used for HVAC condensate lines. Outside diameter includes wall thickness and can vary with material, so it doesn’t indicate how much fluid can pass. A smaller inside diameter would restrict drainage, and sizing by outside dimensions would lead to mismatches with standard fittings. So, three-quarters of an inch inside diameter is the correct specification.

The key idea is that drain lines are sized by inside diameter because that is the actual passage the condensate travels through. The required size is three-quarters of an inch inside diameter. Using inside diameter reflects the true flow capacity and matches the standard fittings used for HVAC condensate lines. Outside diameter includes wall thickness and can vary with material, so it doesn’t indicate how much fluid can pass. A smaller inside diameter would restrict drainage, and sizing by outside dimensions would lead to mismatches with standard fittings. So, three-quarters of an inch inside diameter is the correct specification.