Question about Heater in the Winter. Not blowing warm air if temperature is below a certain point?

Looking for a few opinions and advice on this because I am not sure what is going on.

In the winter, my AC/heater unit blows 65-70~ degree air if the outdoor temperature if below about 45 degrees farenheit. Does anyone know what is causing this?

Based on a quick search I ran, it looks like I have a heat pump based on the above symptom. Also, I am like 99% sure the heating unit I have burns natural gas because my bill jumps by 2-3x in the winter.

Any advice?

submitted by /u/uracowman
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