I used the duty cycle of my existing furnace to calculate the size of a replacement heat pump. The HVAC contractor salesperson at Gen3 didn't seem to use that information though. I thought the modulation of the Mitsubishi system would still be ok, but it wasn't. The minimum BTUs for the new system are still high enough that the system doesn't modulate.

Based on the energy usage and efficiency of the new system, the previous duty calculations seemed to be accurate for the heating load! It's nice to see this method discussed.