Question

all of these are causes for inoperative heat pumps in heating mode except
the outdoor temperature is 47°f
the system is set for emergency heat
the outdoor temperature is -10°f
the outdoor temperature is below the balance point temperature and the back - up heat is a gas furnace
the outdoor temperature will result in a cop of 0.85 and the back - up heat is electric

Explanation:

Step1: Understand heat - pump operation

Heat pumps work well in moderate temperatures.

Step2: Analyze each option

• Outdoor temp of 47°F is a relatively mild temperature and should not cause inoperability.
• Emergency Heat setting bypasses heat - pump operation.
• Outdoor temp of - 10°F is very cold and can cause issues.
• Below balance - point temp with gas furnace backup can lead to inoperability.
• Low COP (Coefficient of Performance) with electric backup can cause inoperability.

Answer:

the outdoor temperature is 47°F