Service capacity · planning precheck

100 amp panel EV charger & heat pump precheck

Add a measured or professionally calculated existing peak to the new loads you are considering. The result exposes arithmetic headroom and a possible load-management path — it does not approve an installation.

Rules reviewed · model as of

New loads that could run together

What this precheck actually tells you

It compares a user-supplied existing peak with new loads that could run together. For example, a 100 A service with a 55 A existing peak, a 32 A EVSE, and an 18 A heat-pump planning load sums to 105 A — 5 A over the service label by simple arithmetic. The same inputs leave 27 A for EV charging while the other entered loads run, which makes a lower charge rate or approved load-management system worth discussing.

That worked example is a transparent screening calculation, not a conclusion that a 27 A setting is legal or sufficient. Your electrician must apply the adopted code and equipment data.

Why a panel upgrade is not the only question

DOE is actively studying residential electrification under panel constraints and capacity management that prevents overcurrent. PG&E's homeowner guide also describes circuit sharing, smart panels, and smart breakers; its example shows a 100 A home using lower-wattage equipment and managed loads. Those are options to evaluate, not universal approval shortcuts.

Also separate service capacity from physical panel space and condition. A home can have arithmetic headroom but no suitable two-pole spaces, obsolete equipment, conductor limitations, or a utility-side constraint.

Official sources and model limits

Source check: . Model rules as of . We use these sources for the planning workflow, EVSE 125% branch-circuit explanation, and load-management discussion. We do not reproduce a jurisdiction-specific NEC service calculation. The yellow “tight” state is our own conservative planning flag when the simple margin is below the larger of 10 A or 10% of service rating; it is not an NEC or local-code threshold.

FAQ

Can a 100 amp panel handle an EV charger and a heat pump?

Sometimes, but the panel label alone cannot answer it. The decision depends on existing demand, the actual EVSE output, the heat-pump load used in the service calculation, equipment that can run together, panel condition and space, utility constraints, and local code. Use this page only to prepare the inputs and questions for a licensed electrician and your authority having jurisdiction.

Should I add up the breaker handle ratings to find my existing load?

No. Breaker handles do not describe how much the home uses at once. PG&E's official guide recommends working with an electrician to use interval data or an appropriate load assessment. Enter a measured or professionally calculated existing-demand value here rather than adding breaker labels.

Why does a 32 amp EV charger show a 40 amp branch-circuit precheck?

DOE's EVSE training explains that the EVSE branch-circuit rating must be at least 125% of the EVSE maximum load current: 32 amps times 1.25 is 40 amps. That branch-circuit check is not the same as a whole-home service load calculation.

Can load management avoid a panel upgrade?

It can in some homes. DOE describes capacity-management solutions, and PG&E describes circuit sharing and smart controls that can pause or reduce EV charging when other large loads run. The device, fail-safe behavior, installation, and local approval still need professional review.

Does an arithmetic margin mean my project is approved?

No. The tool uses simple addition on a 240-volt-equivalent amp basis. It does not apply the required dwelling demand factors or inspect the service, panel, conductors, breaker space, equipment nameplates, utility capacity, permits, or local amendments.

Estimate EV charger installation cost Check conductor ampacity and voltage-drop inputs Plan heat-pump costs Read VoltTally's methodology

Planning precheck only — not electrical advice, an NEC load calculation, a permit decision, or an installation approval. Confirm all values and requirements with a licensed electrician, your utility, equipment instructions, and the authority having jurisdiction.