ASIDE: happy to take this off line too.
Curious about your electrical subpanel number of circuits (breakers) as we are designing our next house?
Can you describe yours please? (and/or picts)?
A) Here is what my kids heatpump and backup resistance heater support looks like in his panel -- SIX 240v slots:
240v 30a using 2 slots : Heat pump
240v 60a using 2 slots : Fan Coil Electric Heater (temps 32F)
240v 60a using 2 slots : Fan Coil Electric Heater (temps 32F)
Article related to needing the backup resistance fan coils:
Will a Heat Pump Work in Cold Weather? - Minneapolis Saint Paul Plumbing Heating Air
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B) Also what about your electric tankless. One I'm looking at use FOUR 240v slots. 40a * 2 circuits.
240v 80a using
4 slots : Electric Tankless Water Heater (eg. Stiebel Eltron Tempra 20)