when I looked into this for my house I found that gas was more like 10x cheaper than electricity. So a 3-4x efficiency advantage for a heat pump still made no economic sense
Depends on where you live, and how you get your electricity. Where I live, Idaho, electricity is very close to beating out gas for heating.
My gas costs $0.51 per therm, including distribution. When I consume electricity (more on that in a sec) it costs me $0.085 per kWh. On a straight therm to kWh basis, electricity is ahead.
But a single therm is equivalent to 29.3 kWh, so on an energy equivalent basis we've got $2.49 worth of electricity per therm of gas. So for 100% efficient electric radiant heat, electricity is about 5x more expensive than gas. That's close to the efficiency band of an air source heat pump, which tends to run in the 200-300% efficiency range, and geothermal might just beat out gas per BTU transferred into the house, especially if you include hot water consumption in that.
The extra complication is solar. Roof top solar is getting cheaper every single day, and for some of us the effective cost of electricity is $0. If you've got a rooftop solar system it's kind of silly not to switch over to electric heating if possible, since you can get your electricity cheap. Especially if you have net metering or a backup battery. If I didn't have a really high efficiency furnace in my new house, I'd probably have already done that.
Correct; unfortunately I can’t price that effectively for my specific house since I bought it with the solar, and can’t separate the numbers out cleanly.
That being said, we know that in the long run rooftop solar reduces electricity cost, because otherwise most people would never buy it. From my numbers above rooftop solar only needs to reduce electricity prices by ~40% to put them within striking distance of a heat pump being cheaper than gas.
