The AI is recommending I NOT use heat pumps, please help me sort this out. – GreenBuildingAdvisor

The house:  I am building a 5400 sq ft home at 8500 ft in Colorado between kinda between Canon City and Guffy CO.  The house is framed up and the outside is almost complete.  The exterior walls from the outside in:  Hardie plank siding / 2×4 furring strips (they were cheaper than 1×3 or 4’s), house wrap / 3.5 in of recycled Polyiso / house wrap again / 7/16 OSB / 2×6 exterior wall framing / not installed yet, but correctly installed and detailed fiberglass batt in the stud bays / 1/2 in drywall.  The ceiling will be well sealed drywall covered by 18-20 inches of blown in cellulose.  The windows are Alpine triple pane Zenith series.  All the doors but the front are fiberglass, the front double door is natural mahogany with some double pane glass.

The floor is: LVP with thin padding / 4 in concrete / heavy mill plastic / 2 in of EPS foam board / 6 in of gravel, the hydronic PEX pipe is 1/2 in and 12 in on center.  The stem wall is separated from the slab with 4 in of EPS.  I have done most of the work with myself and a helper so it is well detailed and very tight.  The ERV is a Renew Aire EV Premium X.  The backup heating system is a propane condensing boiler.  There is a 40 gallon buffer tank that has dual 4500 watt heating elements and a 132 gallon indirect DHW tank with dual 4500 watt elements already purchased that can supply extra heat at night if needed.  After battery charging the solar panel production will be automatically diverted to both water tanks.  The zone is 5a, the design temp is 0F.  Based on advice in this forum I switched from epoxy flooring to LVP with thin padding.  The solar system is being installed now and is 16kw of panels connected to 49kWh of batteries.  I was using the AI to calculate how many more panels/batteries would be needed to support a 5 ton Arctic heat pump.  When it gave me this:

You Can Skip the Heat Pump Entirely and Go Pure Electric-Thermal

At your location (8,500 ft, 45° ground-mount, super-insulated slab, 172 gallons of water + 18 kW of existing elements), it is now the cheapest, simplest, and most bullet-proof off-grid heating solution you can build in 2025.

You essentially turn the two tanks into a giant 170-gallon electric boiler that is charged for free every sunny day and coasts through the night (and multi-day clouds) on stored heat + your batteries.

Real Numbers for Your Exact House (Jan worst-case month)

Your existing 36 × 445 W panels already make ≈ 80–100 kWh/day in January on a sunny day. You need ≈ +180 kWh/day average in the darkest month.

Final Shopping List (DIY pricing, pure electric-thermal, zero heat pump)

What This Buys You

• 100 % solar heated + unlimited DHW, zero propane, zero generator, zero heat pump
• Tanks charge to 165–170 °F every sunny day with the 18 kW elements
• Night/cloudy periods: slab + tanks coast on stored heat; batteries only run circ pumps and house loads (≈ 40–60 kWh/night worst case)
• Even a full week of clouds in January leaves you with >50 % battery at sunrise and tanks still above 110 °F
• System is now idiot-proof: no refrigerant, no compressors, no altitude derating, no defrost cycles

Comparison to Any Heat-Pump Plan

Bottom Line

Skip the heat pump completely. Add 44 more panels and 9 more of your $800 batteries (round numbers) and you are done forever.

You will spend less money, have zero moving parts that care about altitude, and still wake up to toasty floors and unlimited hot showers every single day of the year — even in a January blizzard.

This is now the single best path for your specific house, location, and DIY capabilities. Go for it.