What a heat pump addition actually adds to your solar needs
The baseline addition at a typical home size
A 2,000 sq ft home in a moderate climate replacing a gas furnace with a heat pump needs about 4.8 kW of extra solar capacity, around 12 panels. For a different home size entirely, the fixed-size home tools give a full-home baseline to add this addition on top of. The same 2,000 sq ft home in a cold climate with a cold-climate-rated unit needs closer to 7.2 kW, a 50% jump from climate and equipment type alone.
Replacing a furnace costs more capacity than adding to AC
Replacing a gas furnace adds a whole new electric heating load on top of whatever the home already used. Adding a heat pump to replace an existing central AC only adds the heating portion, since cooling capacity was already electric. For the same 2,000 sq ft moderate-climate home, that's roughly 3.2 kW versus 4.8 kW, a real difference driven entirely by what's being replaced.
Why cold-climate units need a real adjustment
Cold-climate-rated units run defrost cycles and work harder to extract heat from very cold outdoor air, adding roughly 10% more electricity use compared to a standard unit in the same climate. This tool adds that adjustment directly rather than folding it into a generic climate factor that treats all heat pump models the same, an approach that still lands well within the roughly 65% reduction in heating electricity the Department of Energy attributes to modern heat pumps over resistance heating.
Why this is a different tool from sizing a whole all-electric home
This tool sizes just the extra capacity a heat pump addition needs on top of an existing system. The all-electric home tool sizes an entire home with no gas backup at all, covering heating, water heating, and other electric loads together, a much larger number for a very different situation.
What to do with this number next
Add this extra capacity to whatever your existing system already covers, then check the federal ITC calculator for heat pump specific programs. A heat pump also becomes your largest winter load, so if the power goes out in a storm, backup planning changes with it, a scenario the winter storm backup planning calculator sizes around directly.