Outdoor reset control adjusts hot water temperature based on outdoor temperature, resulting in the hottest water during which condition?

• A. Very mild outdoor conditions
• B. Coldest outdoor conditions
• C. Night setback
• D. Morning-only operation

Answer: (B)

Outdoor reset controls adjust the heating water temperature based on how cold it is outside. The colder the outdoor air, the higher the water temperature needs to be to compensate for heat loss and keep the indoor space comfortable. Because of this, the hottest water produced occurs during the coldest outdoor conditions. When outdoor temperatures are mild, the system doesn’t need to run as hot, saving energy. Night setback and morning-only operation are scheduling adjustments that affect when heat is delivered, not the outdoor-based temperature modulation that drives the hottest supply, so they don’t determine when the water is hottest.