I just built a 2000 square foot edition (1500 square feet of it heated, rest is the garage), and happen to have the BTU loss calcs handy. Dropping the thermostat by 3°F would reduce heating loss by about 700 BTU/hr (200W of heating). For a heat pump with a COP of 3-4x, that's about 60W at the meter. Saving, maybe, $1 a month to drop the temp overnight while you're sleeping
My thermostats are the smart electronic kind so I have them programmed to drop the temp 2° at night anyhow.
