A residential heat pump operates in heating mode when the outdoor temperature drops to -15°C (5°F). The homeowner complains of cold drafts and insufficient heating. Which of the following is the most likely primary cause of this issue?

Question: A residential heat pump operates in heating mode when the outdoor temperature drops to -15°C (5°F). The homeowner complains of cold drafts and insufficient heating. Which of the following is the most likely primary cause of this issue?

Answer options: ✅ The heat pump's capacity has significantly diminished at this low ambient temperature, requiring supplemental heat.

• The defrost cycle is occurring too frequently, leading to prolonged periods without active heating.
• The indoor fan motor is failing, resulting in reduced airflow over the indoor coil.
• The outdoor coil is excessively dirty, impeding heat transfer from the ambient air.

Correct answer: The heat pump's capacity has significantly diminished at this low ambient temperature, requiring supplemental heat.

Explanation: At very low outdoor temperatures, the coefficient of performance (COP) and heating capacity of an air-source heat pump significantly decrease, necessitating the activation of supplemental heating such as electric resistance elements or a furnace.