Anyone regret or love having only heat pump(s) for zero F winters? – GreenBuildingAdvisor

Big question for us: do we go all-in on 100% heat pumps?  Or do we go with hybrid heat pumps?  The energy engineer is all-in on heat pumps and thinks we should be fine.  The experienced HVAC contractor leans hybrid heat pumps.

Looking for community experience and feedback.  I’m a mechanical engineer and believe in math.  But the real world doesn’t always exactly follow the mathematical model.

We are doing our best to insulate and seal our existing home within our budget:

R-42 roof (closed cell) – was R-4 at best

R-19 walls (continuous) – was R-13

Double pane windows (L0ewen casements and picture windows) – was all single pane

ACH unknown

4 bedrooms downstairs; 1 bedroom upstairs with kitchen and living room

We had an energy study done (peak heating loads) for the upstairs and downstairs (2 zones, 2 heat pumps) at two target temps (-5F worst case, 10F typical outdoor; 65F indoor):

-5F: 18.4k btuh (upstairs), 30.3k btuh (downstairs)

10F: 14.2k btuh (upstairs), 23.2k btuh (downstairs)

For context, our baseline peak heating loads before insulation:

-5F: 58.5k btuh (upstairs), 36.1k btuh (downstairs)

10F: 45.7k btuh (upstairs), 27.8k btuh (downstairs)

The added insulation hypothetically reduces are HVAC kWh footprint by 63%.

We added a direct vent fireplace as back-up heat if there’s an extended power outage (we also added a 38kW back-up genset).

But now it’s time to call the ball – 100% cold climate heat pumps?  Or hybrid heat pump?

In principle, I generally lean toward hybrid solutions for extreme conditions for their extra flexibility in the face of unknowns.  On the other hand, taking into account green and climate principles, I’d love to go 100% heat pump (if it’s practical and comfortable).

Would love to hear your real world experience!