> assume you have an AC unit as well as a gas furnace A typical Texas house has one unit that is both AC and furnace. Most houses built in the last 50 years h

> assume you have an AC unit as well as a gas furnace A typical Texas house has one unit that is both AC and furnace. Most houses built in the last 50 years have central AC. Given that you'll have ducts, the simplest and easiest way to heat the house is to use them. In other words, it's forced air heating. It's really not a great form of heating, but it's adequate for relatively short, mild winters. So if you replace your one AC/furnace unit with a heat pump unit, you probably won't have a gas furnace anymore to do the comparison. (Apparently, there is such a thing as a "dual fuel heat pump", though, which can heat with gas or heat pump. I'm not sure how much those cost.) Another factor is that AC is the bigger concern for energy usage because AC is used much more of the year. So when replacing your system, whatever money you can spend on an upgrade, you're probably better off putting it toward improving AC efficiency rather than heat efficiency. Or toward something that will help with both, like insulation.