Often this combination will not fit a 100-amp service once you include the heat pump’s backup heat strips, and sometimes it will not fit even with the compressor alone. Do not order both pieces of equipment and hope the panel will accept them on install day.
Backup strips are the usual surprise: they can dwarf the compressor and are easy to skip when someone is eyeballing the panel. Same 1,800 ft² all-gas house, 32 A charger, and an example 6,000 VA heat-pump heating nameplate (compressor only — replace with your outdoor-unit nameplate):
| Step (2023-style optional method, educational) | Result |
|---|---|
| General lighting at 3 VA/ft² | 5,400 VA |
| Small-appliance and laundry circuits at 1,500 VA each | 4,500 VA |
| General load including listed nameplates and EVSE | 17,580 VA |
| First 10 kVA at 100%, remainder at 40% | 13,032 VA |
| Larger of the heating or cooling values entered, at 100% | 6,000 VA |
| Calculated load | 19,032 VA · 79.3 A at 240 V |
| Compared with this walk-through’s service rating | 79.3 A is under a 100 A rating by 20.7 A |
Educational walk-through of the optional dwelling-unit method structure in NEC 2023 220.82. Not a permit calculation. 220.82(C) heating/cooling selections can be more involved than “the larger of two numbers,” especially with heat-pump backup strips.
That compressor-only walk-through is about 79.3 A. If the heating value you must enter is 10 kVA of strips, it becomes about 96.0 A. At 15 kVA of strips it is about 116.8 A, which exceeds 100 A in this example. Those strip figures are labeled examples, not a typical package. Off-ramps include a smaller charger setting, dual-fuel backup, a listed energy management system, or a 200-amp heavy-up. Start with the calculator.
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.