All-electric houses: heat pump, range, dryer and a car

Nameplate addition assumes the oven, the dryer, the water heater, the auxiliary heat strips and the car all pull full current in the same minute, in a house with two or three people in it. It is a useful worst case for a factory. It is a poor description of a kitchen.The code has always known this, which is why Article 220 discounts loads that do not coincide. There are two methods for a dwelling, a standard one and an optional one, and there is a third path that matters most for the house you are describing: the code permits an electrician to use recorded maximum demand from your actual service rather than assumed loads. Where a full year of utility demand data exists, that can be used. Where it does not, a recorded peak over at least thirty days does, and the calculation is that measured peak with a factor applied, plus the new load.That last method is the one that changes outcomes on all-electric houses, and it is the one most homeowners have never heard of. A house with a heat pump and a range on a 200-amp service typically peaks far below where the nameplate sum lands. If your electrician has a recording meter and thirty days, you may be buying nothing at all.

The awkward overlap is auxiliary heat and overnight charging, because a cold snap puts the strips on at four in the morning and that is exactly when a naive charging schedule is still running. The fix is not a bigger service. It is either a start time that finishes before the coldest hours, or a device that watches the whole-house current and backs the charger off when the strips call.The car has slack that no other load has. A heat pump cannot decide to warm the house tomorrow. A car parked from seven in the evening to seven in the morning has twelve hours to take on what a commute used, and it does not care which of those hours it gets.

This is the single most useful rule in this subject and almost nobody explains it. Article 625 provides that where an energy management system limits the EV supply equipment load, the value used in the service and feeder calculation is the maximum that system permits. The management system itself is covered by Article 750. In plain terms: install a device that will never let the charger exceed, say, twenty-four amps when the house is busy, and your load calculation carries twenty-four amps, not forty-eight.There are two flavours in the field. Some chargers do it natively with a current transformer clamped on the service conductors, which is the cheap version and is built into several mainstream units. Some are separate panel-mounted controllers, which cost more and handle more than one load. Either way you are spending hundreds rather than thousands, and jurisdictions generally accept it because the code explicitly contemplates it.The trade-off is real but small. On the handful of nights when the house draws hard, the car charges slower. Since almost nobody uses the full capacity of an overnight window, that is a cost you will not notice.

The expensive pattern is sequential and it is extremely common. Year one, a heat pump goes in and the contractor finds room. Year two, an induction range replaces the gas one and the electrician finds room. Year three, the car arrives and there is no room, so the service upgrade happens now, at the worst possible moment, with two circuits already run to positions that no longer make sense.The cheap pattern is one conversation. Tell an electrician everything you plan to electrify over the next five years and have them calculate against that list. The answer is one of three: you have room for all of it, you have room with energy management, or you genuinely need a larger service. Each of those is a decision you make once.The same logic applies to conduit and panel position. If the service is being upgraded, that is the moment to put the panel somewhere useful and to leave spare capacity and spare conduit. Coming back is what costs money, not the copper.

There are all-electric houses on 100-amp services with resistance heat where the measured winter peak leaves nothing, and no amount of scheduling fixes that. There are panels with no spare spaces and no room for a subpanel. There are Federal Pacific and Zinsco panels that nobody will add to at any capacity. In those cases the upgrade is buying you the whole electrification program, not the car, and it should be priced that way.A residential service upgrade commonly runs $1,500 to $3,000 for the electrical work alone, with the panel itself between $500 and $5,000 depending on size. What makes it unpredictable is the utility side: the service drop, the meter base, the mast, and in older housing the grounding electrode system. Ask which of those are in the quote and which are exclusions, because that is where an estimate turns into a different number.One thing not to do is upsize on instinct. Four hundred amps to a single-family house is a large expense that a measured demand calculation plus energy management would very often have avoided. Buy capacity you have evidence you need.

Ask the electrician which method they used. Standard calculation, optional dwelling calculation, or recorded existing demand. If they eyeballed the panel, you do not have an answer, you have an opinion, and the difference between those two is several thousand dollars.Ask whether energy management was considered and, if it was rejected, why. There are good reasons, including a jurisdiction that does not accept it, but the reason should be stated rather than assumed.And ask for the service work and the EV circuit as separate lines. If the service is going up anyway for the heat pump, the charger circuit is the cheapest thing on the invoice.