Hvac peoples

Conventional air to air heat pump is not effective below about 40F but works efficiently in the range 40-70F. It is just an air conditioning system that also works in reverse.

I would say its worth considering, but strongly suggest you have LP or natural gas as an auxiliary heat source. Heat pumps typically come with an electric heat strip installed inside the air handler that functions as the auxiliary heat - in mild climates this conditions a home in winter at reasonable cost, but gets very expensive in more extreme climates or unseasonably cold winters. All depending on your local price per kW/hr of course.

Building on what Phreakish wrote, you do need to ensure older homes are "tight" - good insulation, good seals on doors and windows, to avoid issues installing AC in homes that previously didn't have it.

And just a tip on the equipment...if you purchased a heat pump with gas furnace as your auxiliary heat, you would be provided with a new furnace not unlike your own, and a case coil to sit on top. The case coil is the same, whether you have a conventional outdoor ac unit, or heat pump. It would be fitted with a different metering device for sure. All that said, you could technically purchase a heat pump, and with some adjustments to the controls, operate it exclusively as a conventional ac unit, cooling only, and rely on your furnace 100% for heat.