Which combination of minimum indoor temperature and height above the floor is specified for the design heating day?

Which combination of minimum indoor temperature and height above the floor is specified for the design heating day?

• A. 68 degrees F at 3 feet
• B. 70 degrees F at 4 feet
• C. 72 degrees F at 3 feet
• D. 65 degrees F at 2 feet

Answer: (A)

In HVAC design, the design heating day uses a standard indoor condition to estimate heating loads: a comfortable minimum temperature setpoint measured at a height that represents the occupant’s breathing zone. The convention is 68°F at 3 feet above the floor. This height choice accounts for slight temperature stratification and ensures the condition reflects where people actually experience the air, not near the floor or ceiling. That’s why the combination of 68°F and 3 feet is the proper reference point for heating-day design. Other options propose higher or lower temperatures or different heights, which aren’t the standard reference used for calculating heating loads. They would lead to inconsistent or nonstandard results compared with the established design practice.

In HVAC design, the design heating day uses a standard indoor condition to estimate heating loads: a comfortable minimum temperature setpoint measured at a height that represents the occupant’s breathing zone. The convention is 68°F at 3 feet above the floor. This height choice accounts for slight temperature stratification and ensures the condition reflects where people actually experience the air, not near the floor or ceiling. That’s why the combination of 68°F and 3 feet is the proper reference point for heating-day design.

Other options propose higher or lower temperatures or different heights, which aren’t the standard reference used for calculating heating loads. They would lead to inconsistent or nonstandard results compared with the established design practice.