What Size Electrical Panel Does a New Home Need? Honest 2026

What size electrical panel does a new home need in Idaho?

A 200-amp service with a 40-space panel covers most new custom homes in Teton Valley and Eastern Idaho. That is the default I start from, and I only move off it when the math forces me to.

Here is the part people get backwards. The size of your house does not decide the electrical panel. The loads decide it. A 4,000 square foot house with propane heat, a propane range, a propane water heater and one car in the garage can run comfortably on 200 amps. A 2,400 square foot house that is all-electric — heat pump, electric backup heat, induction range, heat pump water heater, hot tub, two EVs — can push past it. I have built both. The smaller house needed the bigger service.

So when somebody asks me what size electrical panel their new home needs, my honest answer is that I cannot tell them until we have made the mechanical decisions. Heat source, water heater, range, and whether there is a shop, a well or an EV in the picture. Those five answers write the number. Everything else is rounding.

What is a load calculation, and why does it decide the number?

A load calculation is the arithmetic an electrician runs to prove your service is big enough. It is not a guess and it is not optional — the building department wants to see it, and the number it produces is what sizes your electrical panel, your meter base and the wire coming in from the transformer.

Idaho runs on the 2023 National Electrical Code, adopted by the state at IDAPA 24.39.10, Section 600. For houses, almost everybody uses the optional method in NEC 220.82, which works like this:

• General load: 3 VA per square foot of living space, plus 1,500 VA for each of the two required kitchen small-appliance circuits, plus 1,500 VA for laundry.
• Fixed appliances: the nameplate rating of everything hard-wired or on its own circuit — range, dryer, water heater, well pump, hot tub, EV charger.
• The demand factor: the first 10 kVA of all that counts at 100%, and everything above 10 kVA counts at only 40%. This is the step that saves you. The code assumes you are not running the oven, the dryer and the hot tub at the same instant.
• Heating and cooling: you add only the largest one, not all of them. A heat pump with electric backup counts at 100% of the heat pump plus 65% of the backup strips.

Divide the total by 240 volts and you have your amps. EC&M has a clean walkthrough of the full method if you want to see it worked out line by line.

What that 40% demand factor means in practice: a lot of houses that feel like they need 400 amps calculate out in the 180–220 amp range. I have had clients arrive convinced they needed a 400-amp service because a neighbor told them so, and the calculation came back at 190. We put in a 200-amp electrical panel with spare breaker spaces and they have never tripped a main in four winters.

200 amp or 400 amp: which one does my house need?

Here is the decision table I actually use when we are setting the mechanical scope on a build. Find the row that describes your house.

Your house has	Typical calculated load	What I spec
Propane heat, propane range, propane or gas water heater, one car	110–160 amps	200-amp service, 40-space panel
Heat pump, propane backup, induction range, one EV charger	150–200 amps	200-amp service, load-managed EV circuit
All-electric, heat pump with electric strips, induction, heat pump water heater, one EV	190–260 amps	200-amp with energy management, or 320/400-amp
Any of the above plus a well pump and a hot tub	add 25–45 amps	400-amp service gets serious
Detached shop or guest space on the same meter	add 40–100 amps	400-amp service with a subpanel feed
Two EV chargers, no load management	add 80 amps	400-amp service

A note on the middle option, because it is the one most people have never heard of. A “320-amp” meter base — sometimes sold as 400-amp — feeds two 200-amp panels instead of one giant one. On a house with a shop or a guest wing it is often cleaner and cheaper than running a single oversized electrical panel and a long feeder.

And the honest caution: going bigger is not free and it is not automatically better. A 400-amp service means a bigger meter base, heavier wire, sometimes a bigger transformer on the utility side, and a second electrical panel to land it all. If the calculation says 190 amps, paying for 400 buys you a number on a sticker. Spare breaker spaces and a conduit stub buy you actual future capacity for a fraction of the money.

What does an EV charger actually add?

This is the question driving most of the panel-size anxiety I hear right now, and the code has a specific answer. Under the 2023 NEC, section 220.57 says an EV charger counts in your load calculation at 7,200 VA or its nameplate rating, whichever is larger. At 240 volts that is 30 amps of calculated load for a typical unit, and a 48-amp charger counts for more.

	Level 1	Level 2	Level 2 with load management
Circuit	Existing 120V 20A outlet	240V, 40–60A breaker	240V, breaker sized to the managed limit
Miles of range per hour	3–5	25–40	25–40, throttled when the house is busy
Counts against your service	Negligible	7,200 VA minimum under NEC 220.57	Can be counted at the managed value
Good for	A plug-in hybrid, or a second car	Any EV, the normal choice	Avoiding a service upgrade

The thing worth knowing is the escape hatch. The 2023 code added real support for energy management systems — NEC article 750, with 625.42 allowing more than one charger on a circuit when an energy management system controls them. In plain English: a device watches the whole house, and when the dryer and the oven are both running it quietly dials the car charger back. The car still charges overnight. You never notice. And the load calculation gets to count the managed number instead of the full 7,200 VA.

That one device has kept several of my clients on a 200-amp electrical panel when the raw math said they needed 400. It costs a few hundred dollars. A service upgrade costs thousands.

Should I run conduit now if I do not own an EV yet?

Yes. Every time. This is the cheapest insurance in the whole house.

While the garage walls are open, running a length of conduit from the electrical panel to the wall where a car will park costs very little — it is an hour of an electrician’s time and some pipe. Doing the same job after drywall, paint and finished storage cabinets means cutting, patching, repainting, and a bill with a four-figure number on it. I put a conduit stub and a blank box in the garage of houses whose owners swear they will never own an electric car. Two of them called me within three years.

The same logic runs through every decision made while the walls are open, which is the whole argument in my post on which custom home upgrades are actually worth the money. The test is simple: can you change it later without tearing something out? Paint colors, yes. Conduit behind drywall, no.

What I leave behind on a house that is not getting a charger on day one: the conduit, a blank box at charger height, two spare breaker spaces reserved in the electrical panel, and a note in the closeout binder saying what the conduit is and where it lands. That last part matters more than people think — a stub nobody can identify in five years is a stub nobody uses.

What does Idaho code require that the national code does not?

Idaho writes its own amendments on top of the national code, and two of them change what your house actually gets. Most builders never mention either one.

Arc-fault protection is narrower here than almost anywhere else. The national code requires arc-fault breakers on branch circuits through most of a dwelling — bedrooms, living rooms, kitchens, hallways, the lot. Idaho amends NEC 210.12 so that in one- and two-family dwellings, in the state’s own words, “Arc-Fault Circuit-Interrupter Protection shall only apply to all branch circuits and outlets supplying bedrooms.” Bedrooms only. Everywhere else in your house, the arc-fault breaker is optional.

That is a real fork in the road, and it is one of the few places where I spend money the code does not make me spend. Arc-fault breakers cost more than standard ones, and on a 40-space electrical panel going beyond bedrooms adds a few hundred dollars. I think it is worth it in a house full of wood, at the end of a long rural feeder, hours from a fire station. But it is your money, and you should know it is a choice rather than assume the code handled it.

Whole-house surge protection is required. Idaho keeps NEC 230.67 in force, so new dwelling services get surge protection at the electrical panel. This one catches people who priced an electrical package in another state. It is not an upgrade here. It is the baseline, and given how often lightning and utility switching hit rural feeders in this valley, I would install it regardless.

Both amendments live in the same state rule that adopts the code, and your inspector works from it. Which inspections hit the electrical scope, and in what order, is covered in my guide to what custom home inspections actually happen. County-by-county permit paths are on the Idaho building permits page.

Where should the panel go in a snow-country house?

Somewhere you can reach it in February. I am not being glib — I have stood in front of an exterior meter base buried to the latch in drifted snow, and the homeowner had no way to kill power to his own house.

What I do on a Teton Valley build:

• Meter outside, electrical panel inside. The utility needs to read the meter. You need to reach your breakers without going outdoors in a storm.
• Mechanical room, not the garage wall behind where the truck parks. The code wants 30 inches of clear width and 36 inches of working depth in front of the panel, and that space has to stay clear for the life of the house. A garage panel becomes a shelf by year two.
• Out of the drift and off the drip line. Roof shed on a metal roof in this snow load will bury anything beneath it, which is the same reasoning behind where vents and intakes land, covered in my post on whole house ventilation.
• Next to the mechanical equipment, not across the house from it. Heat pump, water heater, ventilation unit and well controls all want short home runs from the same electrical panel.

If the house has a heated garage or a room above it, that changes the circuit count too — a conditioned garage with a mini-split, a charger and a shop bench is three dedicated circuits before you have plugged anything in.

Who pays to get power to my lot?

You do, and this is the line item that blindsides people buying raw land.

Most of Teton Valley is served by Fall River Rural Electric Cooperative, and the rest of the Eastern Idaho corridor by the investor-owned utilities. Either way, the drill is the same: the utility brings power to a point, and from there the trench, the conduit, the wire and the transformer pad are the project’s cost. On an in-town Driggs lot with a transformer across the street, that is modest. On a 20-acre parcel where the nearest line is a quarter mile away, a service extension can run into the tens of thousands, and the utility’s engineering queue can add months to your schedule.

This is why I walk a lot before anybody writes an offer, and why power is on the checklist in how to prepare land to build a house alongside the well, the septic and the driveway. The order matters: you want the utility application in early, because it runs on their calendar, not yours. The full list of what a per-square-foot number leaves out is in the hidden costs of building a custom home.

What does the electrical package cost?

The figures below are market data, not my rate card. They are what the work generally runs nationally and regionally, published so you can sanity-check a bid. My own construction pricing starts at $400 per square foot of conditioned space and goes up, and the electrical scope is carried inside that, not quoted as a menu.

Item	Typical 2026 market range	Notes
Main panel replacement (retrofit)	median about $3,500	Lawrence Berkeley National Laboratory single-family medians; middle half $2,100–$5,000
Service upgrade, homeowner side	median about $2,800	$2,000–$5,000 for the middle half
Service upgrade, utility side	median about $3,500	$1,650–$7,000; highly location-dependent
Subpanel	about $1,500	Often the cheaper answer for a shop or garage
Level 2 EV charger, hardware	$300–$700	Plug-in 40A units cost less than hardwired 48A
Level 2 charger installation	$750–$2,500	Distance from the electrical panel is the biggest driver
Conduit stub during construction	Fraction of the above	Open walls; this is why you do it now
Rural service extension	Thousands to tens of thousands	Distance to the nearest line and transformer

One timing note that matters this year. The federal 30C credit that used to help with a home charger is gone: under the 2025 tax law the IRS confirms the credit is not allowed for property placed in service after June 30, 2026. The 25C and 25D home-energy credits ended at the close of 2025. If you were building a budget around any of those, rebuild it. There is no federal credit to lean on now, which is another reason the cheap conduit stub beats the expensive retrofit.

What I spec on every house I build

After twenty years of this, here is my standing electrical scope. Not because it is code — most of it is not — but because I have been called back to houses that skipped it.

• 200-amp minimum, 40 spaces minimum, with at least eight spare breaker spaces left open in the electrical panel at closeout.
• A conduit stub to the garage for a future charger, whether or not there is a car for it yet.
• Arc-fault protection past the bedrooms, even though Idaho only requires it there.
• A generator interlock or transfer switch provision. We lose power out here. Roughing it in is cheap; adding it later is not.
• Dedicated circuits for the well pump, the water treatment equipment, the heat pump, the water heater and the ventilation unit.
• A labeled panel schedule and a photo of the open electrical panel in the closeout binder, taken before the cover went on.
• Structured wiring runs pulled at rough-in, which is the backbone under the smart home systems people want later.

None of that is exotic. It is the difference between a house that accepts the next twenty years of change and one that fights you every time something new plugs in. The same thinking drives the energy efficient features worth paying for and the insulation decisions made in the same open walls.

And to be plain about who does what: I am involved in every phase of every build, and the electrical scope gets coordinated through design along with the plans, the engineering and the selections. You do not need to go hire that out. It is handled inside the design agreement, which carries a fixed design fee quoted per project. How the whole thing runs is laid out on my process page.

Frequently asked questions

Is 200 amps enough for a 4,000 square foot house?

Usually, yes. Square footage barely moves the load calculation — general lighting and receptacles only count at 3 VA per square foot, so 4,000 square feet contributes about 12,000 VA before the 40% demand factor knocks most of it down. What decides it is whether the heat, the range and the water heater are electric or propane, and whether there is a well, a shop or an EV charger.

Can I add a bigger electrical panel later?

You can, but it is one of the more disruptive retrofits in a finished house. You are looking at a new meter base, possibly new service conductors, utility coordination, permits and inspections, and market medians put a main panel replacement around $3,500 with the top of the range well past $5,000. Sizing it right during construction costs a small fraction of that.

Do I need a 400-amp service for an electric vehicle?

Almost never for one car. A single Level 2 charger adds 7,200 VA to the calculation under NEC 220.57, which most 200-amp houses absorb. Two chargers without load management is where 400 amps starts to make sense — and even then, an energy management system under NEC article 750 is usually the cheaper fix.

Does Idaho require arc-fault breakers throughout the house?

No. Idaho amends the 2023 National Electrical Code so that in one- and two-family dwellings, arc-fault protection applies only to branch circuits and outlets supplying bedrooms. The rest of the house is exempt. I install them beyond bedrooms anyway, but it is a choice you are paying for, not a code requirement.

Where does the electrical panel have to be located?

Code requires clear working space in front of it — 30 inches wide and 36 inches deep — kept clear permanently. Beyond that it is judgment. In snow country I put the meter outside and the panel inside in the mechanical room, out of the roof shed line and near the equipment it feeds.

Get a real number on your build

If you are planning a custom home in Teton Valley, Jackson Hole or Eastern Idaho and you want the electrical scope settled before it becomes a change order, the next step is a 30-minute planning call. We will talk through your lot, your heat source, whether an EV is in the picture, and what that means for the service. You will get a straight answer on fit — no follow-up loops.

Or call me direct: (208) 520-0636. More on what a build costs overall is in how much a custom home costs in Idaho, and the foundation decision that sets the mechanical room is in basement vs crawl space vs slab. The code itself is published by the NFPA as NFPA 70.

Bryce Swager, SwagerBuilds — 20 years in construction, involved in every phase of every build. Idaho contractor registration RCE-57499. Built different. Built right. Built by SwagerBuilds.