A house converting from gas appliances to electric ones adds four large loads, and the service was sized without any of them.
The four conversions
Heating — a gas furnace to a heat pump. The largest single change in a cold climate, particularly where electric resistance backup is included.
Water heating — a gas water heater to a heat pump water heater or a resistance one. A heat pump water heater draws far less than a resistance one and this choice matters for the calculation.
Cooking — a gas range to induction or electric. A dedicated 240 V circuit, typically 40 or 50 amps at nameplate.
Vehicle charging, which is not a conversion from gas in the appliance sense and behaves like one in the calculation.
Why it does not simply add up
The Code's calculation applies demand factors, and heating and cooling are counted as the larger of the two rather than both.
A house converting heating to a heat pump replaces its cooling load with a combined heating-and-cooling load rather than adding one, which is much less severe than it first appears.
The additions that are genuinely new capacity are the range, the water heater and the vehicle.
The order that keeps the service
Reduce the load before adding to it. Air sealing and insulation lower the heating load, which lowers the size of the heat pump, which lowers what it draws. This is the cheapest capacity there is.
Choose the efficient version of each appliance. A heat pump water heater draws a fraction of a resistance one. An inverter heat pump with a well-chosen balance point uses far less backup strip heat than one without.
Size the EV circuit to the household's actual driving, not to the largest charger available.
Use load management where two large loads would otherwise coincide, which the Code recognises and which is far cheaper than an upgrade.
Keep one gas appliance if the arithmetic is tight and one of them is new — most often the range, which is the most deferrable conversion.
Where an upgrade is genuinely needed
A 60 or 100 amp service with several conversions and no willingness to manage loads.
Electric resistance backup heat in a cold climate, which is a very large load and is not deferrable.
Two vehicles charging alongside everything else.
A panel that is obsolete or at the end of its life, in which case the panel is being replaced regardless and the upgrade is incremental.
Sequencing the work
Each conversion needs a dedicated circuit and a panel position. Doing them one at a time means four separate electrician visits.
Doing the electrical work once — the panel or subpanel, and the circuits run to where the appliances will be — and then converting the appliances as they fail is usually cheaper and less disruptive than either extreme.
Incentives
Federal credits and state and utility programmes support heat pumps, heat pump water heaters, panel upgrades and EV equipment, and several fund the electrical work specifically because it is the barrier.
Income-qualified programmes in several states cover a large share of the whole package. The requirements and the funding change annually and are worth checking before committing to any single piece.
The document to start with
A load calculation showing the house as it is and as it would be after each conversion.
That single sheet tells you which conversions fit, which need management, and whether an upgrade is genuinely on the path — and it costs a fraction of the smallest decision it informs.