Which is better a heat pump or a gas furance?

I getting ready to put in a complete central air conditioning system in my old house. I will need to have complete duct work installed. I have heard that I will either need a heat pump or a gas furance. I would think a gas furnance would be better. Anyone have any ideal what this would run for a 1850 sq ft... show more I getting ready to put in a complete central air conditioning system in my old house. I will need to have complete duct work installed. I have heard that I will either need a heat pump or a gas furance. I would think a gas furnance would be better. Anyone have any ideal what this would run for a 1850 sq ft house, 4 bdrm, 2 baths?
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