Sometimes, after a load calculation — this combination is less favorable than a gas-water-heater house and better than a house with a large electric range. Honda’s published running-watt figure for an electric water heater is 4,500 W (used here only as a stand-in nameplate; use the rating on your tank or heat-pump water heater). A 32-amp charger is 7.68 kW. Together they are a serious add to a 100-amp service, especially if they can overlap, which they can: the tank can recover while the car charges overnight.
Educational optional-method walk-through: 1,800 ft², 4,500 VA water-heater example, 4,000 VA cooling example, 32 A EVSE, compared with 100 A.
| 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 | 22,080 VA |
| First 10 kVA at 100%, remainder at 40% | 14,832 VA |
| Larger of the heating or cooling values entered, at 100% | 4,000 VA |
| Calculated load | 18,832 VA · 78.5 A at 240 V |
| Compared with this walk-through’s service rating | 78.5 A is under a 100 A rating by 21.5 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.
This walk-through is about 78.5 A, under 100 A in this simplified method. It is not a green light. A 5.5 kW or 6 kW tank, a 48 A charger, or an electric range on top can erase the margin, and a measured-demand check adds the 32 A at face value on top of whatever peak already includes water heating. A heat-pump water heater is a different, usually smaller, nameplate — see that 200-amp combination page for the contrast. Use the calculator with your nameplate.
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.