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Short answer: well water pressure in a new Idaho home is not something your driller hands you. It is three numbers working together: how many gallons per minute the well actually produces, how many gallons per minute the house demands at its worst minute of the day, and how much water the pressure tank can hand over before the pump has to restart. Get those three right during design and the house feels like city water. Get them wrong and you own a plumbing problem that no amount of pipe can fix later.

What actually decides well water pressure in a new house?

Four things, in this order.

Well yield. The gallons per minute your well can deliver without pulling the water level in the borehole down below the pump intake. This is a property of the ground, not of your budget. You cannot buy your way past it.

Pump capacity. How many gallons per minute the pump moves against the lift and friction it has to fight. The rule here is absolute: never set a pump bigger than the well. A pump that outruns its well will suck the water level down to the intake, gulp air, and burn itself up.

Tank drawdown. How many usable gallons the pressure tank releases between the pump shutting off and switching back on. This is what carries you through a 90-second handwashing and a toilet flush without the pump ever starting.

Pressure setting and pipe sizing. What psi the switch turns the pump on and off at, and whether the pipe between the well and the far shower is big enough that the pressure survives the trip.

I have been in construction 20 years and I am involved in every phase of every build, which means I have watched this go wrong in all four places. The most common failure is not a weak well. It is a decent well paired with a tank that is too small, so the pump short-cycles, the pressure swings while you shower, and the pump dies years early.

How much water does a custom home need at once?

Not as much as people assume in total, and more than people assume at the peak.

Total daily use for a normal household lands in the low hundreds of gallons. That is rarely the constraint. The constraint is the worst seven minutes of the morning, when two showers, a toilet, a dishwasher and a washing machine all want water simultaneously.

There are two ways the industry sizes for that peak, and they are worth knowing because they give different answers.

The fixture-count method is crude and fast: count every fixture and outlet in the house, including hose bibbs and a hot tub, and call that number your gallons per minute. A house with twelve fixtures gets a 12 gpm pump.

The peak-demand method is better. It looks at the gallons a household actually pulls in a seven-minute window. The Water Systems Council publishes the table most drillers work from, and the numbers are higher than homeowners expect.

Bathrooms in the house	Peak gallons in 7 minutes	Minimum pump size
1	45 gal	7 gpm
1.5	70 gal	10 gpm
2	98 gal	14 gpm
3 to 4	122 gal	17 gpm

Look at the bottom row. A four-bathroom custom home wants 17 gpm at its peak. That is a real number and it is the one that surprises people who were told “we hit water at 180 feet, you’re fine.”

What is not in that table: outdoor irrigation. Lawn and landscape are usually the biggest draw on the whole property, they run for hours instead of minutes, and on an Idaho lot they can also be a water-right question rather than a plumbing one. More on that below.

What counts as a good well, and what counts as a weak one?

Five gallons per minute is the rough line. At or above 5 gpm, a normal house usually needs no supplemental storage at all. Below 5 gpm, you start engineering around it. Below 1 gpm, you are building a water system that happens to include a well.

Here is why a low number is such a problem, using Penn State Extension’s example. A 1 gpm well produces about 1,440 gallons across a full day, which sounds like plenty. But peak periods last 30 minutes to two hours, and a household can pull more than 300 gallons in a two-hour morning peak. That same 1 gpm well only delivers 120 gallons in two hours. The daily total is fine. The morning is a disaster.

The other thing people miss is that the borehole itself is storage. A 6-inch well holds about 1.5 gallons for every foot of standing water, so 100 feet of water column in the casing is roughly 147 gallons sitting there before the pump even has to keep up. That is why two wells with the same gpm can behave completely differently: the deeper one with more water above the pump has a buffer, and the shallow one does not.

In Teton Valley this matters more than most places. Idaho DEQ’s assessment of the valley describes a predominantly unconfined alluvial aquifer, recharged by tributary underflow, stream seepage, irrigation and precipitation, and it notes that shallow groundwater of 10 feet or less is common in the valley, particularly where coarse gravels sit near the surface. Unconfined and shallow means the water level responds to the season. A well tested in June is not telling you what it does in a dry September.

So the honest version is this: until your well is drilled and tested, nobody knows what your well water pressure will be. What we can do during design is plan for the range, and hold the decisions that depend on the answer until we have it.

What happens if the well can’t keep up with the house?

You do not give up and you do not oversize the pump. You add storage between the well and the house, and you let the well fill that storage at whatever slow rate it can manage. A weak well does not have to mean weak well water pressure at the fixture, as long as somebody designed for it.

The standard fix is a two-pump system. The well pump runs at a rate the well can actually sustain and fills an atmospheric storage tank, usually in a mechanical room, a heated garage bay or an insulated vault. A second pump, a shallow-well or booster pump on its own pressure switch, pulls from that tank and feeds the house. The house sees the booster pump and the pressure tank. It never sees the weak well, and the well water pressure at the shower is set by the booster rather than by the ground.

Sizing the storage is straightforward. The rule of thumb Penn State Extension publishes is 100 gallons per person, so a family of five plans on 500 gallons, plus margin for whatever the house will grow into. Published guidance for low-yield wells runs roughly like this.

Well yield	2 bedrooms	3 bedrooms	4 bedrooms	5 bedrooms
5 gpm or better	None needed	None needed	None needed	None needed
3 to 5 gpm	100 gal	150 gal	200 gal	250 gal
1 to 3 gpm	150 gal	200 gal	250 gal	300 gal
0.5 to 1 gpm	200 gal	250 gal	Not recommended	Not recommended
Under 0.5 gpm	Not recommended	Not recommended	Not recommended	Not recommended

There is a second lever most people never hear about: the well itself can hold more water. Penn State’s numbers make the point cleanly. A 6-inch well with 100 feet of standing water holds about 147 gallons. A 10-inch well with that same water column holds about 408 gallons, an increase of 261 gallons. Deepening an existing 6-inch well by another 100 feet adds about 147 gallons. On a marginal lot, a wider or deeper borehole can be cheaper than a tank, a second pump and the mechanical room space to put them in.

The catch: in a dry year, a well that normally carries 100 feet of water may be down to under 20 feet of water column. Widening it then only adds about 50 gallons. In-well storage is real, but it is the first thing drought takes away.

What I will not do is let somebody sign a construction contract on a four-bathroom house with a 1 gpm well and no storage plan. That is a callback waiting to happen, and it is the kind of thing that should get settled before the foundation is poured, not after the drywall is up. Well water pressure is a design-phase decision, not a punch-list item.

What pressure should the system run at: 30/50 or 40/60?

This is the setting that decides what your well water pressure feels like day to day. Modern systems run at one of two settings. The first number is the pressure where the switch turns the pump on, the second is where it turns off.

30/50 psi is the old default. It works, it is easy on the plumbing, and it feels thin in a big house with a long run to the far bathroom.

40/60 psi is what I want on a custom home. It gives you headroom for friction loss on the way to the upstairs shower, and it makes a second-floor fixture feel like a first-floor fixture.

The number that actually matters is not at the tank, it is at the worst fixture. The target to hold is roughly 20 psi at the inlet of the highest and farthest fixture from the pump, measured while the water is running, not sitting still. Static pressure at the tank tells you almost nothing. Flowing pressure at the far end tells you everything, and it is the only honest measure of well water pressure in a finished house.

For context on how little some things need: dishwashers and washing machines want at least 10 psi at their inlet, while lawn sprinklers typically want 20 psi and sometimes up to 40. Sprinklers are the hungriest thing on most properties, which is one more reason irrigation gets designed as its own problem.

Pumps that sit far from the house, or well below it, need higher settings to deliver the same pressure at the fixture, because every foot of lift and every fitting on the way eats into it. On a big lot where the well sits 300 feet from the house, the pressure setting and the pipe size are the same conversation.

How big does the pressure tank need to be?

Bigger than whatever the cheapest bid includes.

This is where most disappointing well water pressure actually comes from, and it is the cheapest thing on the list to get right. Here is the part almost nobody tells homeowners: a pressure tank does not store its own volume. Only about 20 percent of a pressure tank’s rated capacity is usable drawdown. The rest is air charge. Penn State Extension puts real numbers on it.

Tank rated capacity	Actual usable water (drawdown)	What that buys you
42 gal	About 8 gal	A toilet flush and a handwash
82 gal	About 16 gal	A couple of minutes of a single shower
120 gal	About 24 gal	Real buffer on a multi-bath house

So the 42-gallon tank that a builder’s allowance quietly assumes holds eight gallons. Eight gallons is one toilet flush and a pot of pasta water. On a 14 or 17 gpm system, eight gallons of drawdown means the pump restarts in well under a minute of real use.

That is the whole reason tank size matters. Most of the wear on a well pump happens when it starts and stops, not while it runs. A pump that cycles twice as often wears out in roughly half the time. A larger tank is not about comfort, although you will feel it. It is about not pulling a 300-foot pump out of the ground in year seven instead of year fifteen.

On our builds I would rather put the money into an 80 or 120-gallon tank and a correctly set air charge than into a fancier fixture. The fixture is visible and the tank is not, which is exactly why the tank is where corners get cut.

Standard pump and tank, or a constant-pressure system?

A standard system is a single-speed submersible pump, a pressure switch and a pressure tank. The pump is either full on or full off, so your pressure constantly cycles between the two switch settings. You feel that as the shower getting slightly stronger and weaker on a loop.

A constant-pressure system uses a variable-speed drive. The pump speeds up and slows down to hold one pressure, so the well water pressure at a shower feels the same whether somebody is running the dishwasher or not. It also needs a much smaller tank, because the drive is doing the job the tank’s drawdown used to do.

	Standard pump and tank	Constant-pressure (variable speed)	Storage tank and booster pump
Best when	Well yield comfortably beats peak demand	Yield is adequate but the house is big or multi-story	Well yield is below peak demand
Pressure feel	Cycles between the two settings	Steady at one pressure	Steady, set by the booster
Tank needed	Large, drawdown is the buffer	Small	Atmospheric storage plus a pressure tank
Moving parts	Fewest	Drive electronics at the well or in the house	Two pumps, two controls
Field repair	Any pump outfit in the valley	Needs someone who knows the drive	More components to diagnose
Space required	Tank only	Least	Most, by a wide margin

My honest take after 20 years of these: constant pressure is genuinely better to live with, and I will not pretend it is free or maintenance-neutral. It adds electronics to a system that otherwise has almost none, and in a rural valley the question of who can service it at 9 p.m. in February is a fair one to ask before you buy it. On a large two-story custom home with a solid well, it is usually worth it. On a simple single-story with a strong well, a correctly sized tank does the job for less.

One thing that is not optional either way: the pump is an electrical load. A submersible well pump is typically a dedicated 240-volt circuit, and on a rural property it lands on the panel alongside the septic pump, the shop subpanel and whatever else the lot needs. That is a load calculation question, and it is covered in our post on what size electrical panel a new Idaho home needs.

What does Idaho plumbing code actually require?

Idaho adopts the 2015 Uniform Plumbing Code as the Idaho State Plumbing Code at IDAPA 24.39.20, Section 600, and then amends it in a long list of specific places. Four of those amendments touch a well water pressure system directly, and one of them catches people out every single time.

The buried water line has to be 42 inches down. Idaho’s amendment to Section 609.1 throws out the national “below the frost line” language and replaces it with a flat number: the cover over yard piping “must be not less than forty-two (42) inches below grade.” Teton County’s frost depth is 32 inches. So the plumbing rule here is ten inches deeper than frost depth, and the trench from the wellhead to the house gets dug to the plumbing rule, not to the frost rule. Nobody is happy to discover that with a rented excavator and the ground already closing.

Pressure above 80 psi needs a regulator. Where static pressure in the supply piping exceeds 80 psi, UPC 608.2 requires an approved pressure regulator downstream of an adequate strainer, reducing static pressure to 80 psi or less. Regulators 1.5 inches and larger do not need the strainer. An approved expansion tank goes on the cold water distribution piping downstream of each regulator.

There is a detail here that trips up sizing: once you reduce pressure, the piping downstream is sized on 80 percent of the reduced pressure, so a regulator set at 80 psi gives you 64 psi to size against, not 80. High well water pressure is a real condition on steep lots where the well sits well below the house.

The softener loop is mandatory on a lot of houses. Idaho’s amendment to Section 610.2 requires that new one and two-family residences built slab-on-grade, or that will have a finished basement at final inspection, “must have a pre-plumbed water softener loop.” The kitchen sink needs one hot soft line, one cold soft line and one cold hard line, and exterior hose bibbs intended for irrigation must be piped with hard water. Over four bathroom groups, the Table 611.4 footnote sends softener sizing to the manufacturer’s standards.

We cover why that matters on well water in our post on whether a new Idaho home needs a water softener, and the basement-or-slab decision that triggers the requirement is in basement vs crawl space vs slab.

Frost-proof hose bibbs are required, not optional. Idaho’s amendment to 603.5.7 says that in climates where freezing temperatures occur, a listed self-draining frost-proof hose bibb is required. That is every lot we build on.

A couple of smaller Idaho changes are worth knowing because they come up in bids: listed polyethylene water service and yard piping rated at a minimum of 160 psi may run inside the building with one joint using listed metallic transition fittings (605.6.2), the water hammer section does not apply to residential construction (609.10), and the pipe insulation section is deleted outright (609.11). The plumbing inspection that checks all of this is part of the sequence in our guide to what inspections happen on a custom home.

What are the well rules on a rural Idaho lot?

The well itself is governed by the Idaho Department of Water Resources, not the building department, under the Well Construction Standards Rules. These rules decide where the well can physically go, and on a tight lot they can decide the whole site plan.

Minimum separation distances from a well, from Rule 25:

Separate the well from	Minimum distance
Septic tank	50 ft
Septic drainfield	100 ft
Drainfield serving more than 2,500 gpd	300 ft (less with site investigation data)
Effluent pipe	50 ft
Sewer lines	25 to 100 ft, by type
Permanent or intermittent surface water	50 ft
Canals, irrigation ditches, temporary surface water	25 ft
An existing well in separate ownership	25 ft (50 ft for a public supply well)
Permanent buildings	10 ft
Above-ground chemical storage tanks	20 ft
Property line	5 ft

Run the math on a small lot and you will see the squeeze. A well needs 100 feet from your own drainfield and 50 feet from any surface water, the drainfield needs its own setbacks, and the house has to fit between them. On a one-acre parcel with a creek on one edge, that is not a drafting exercise, it is the thing that determines where the house sits. This is exactly the kind of constraint we work out during design rather than discovering at permit.

The construction standards themselves are specific. Casing has to extend at least 12 inches above land surface and finished grade, and a concrete slab counts as finished grade. Wells deeper than 38 feet need a surface seal extending to at least 38 feet below land surface. In the unconsolidated, unconfined formations that make up much of Teton Valley, the casing goes at least 5 feet below the water table and is sealed to at least 38 feet. Grout seals need at least 1 inch of uniform thickness in the annular space, dry bentonite needs at least 1 and 5/8 inches.

On process: a drilling permit is required under Idaho Code 42-235 before construction, and for single-family domestic wells the Director may allow a start card instead, which has to reach the Department at least two office hours before drilling begins. The driller calls the regional office at least four hours before placing any annular seal. Start cards and verbal approvals are generally not available in designated drilling-concern, critical or management areas, which is one of the first things we check on a lot.

The part you should actually care about as a homeowner is Rule 25.25: the driller must measure and record the static water level, the pumping water level and the production rate, using a pump, bailer, air-lift or other industry-accepted test of sufficient duration. That record is your well’s report card. It is the document the pump gets sized from, which makes it the document your well water pressure is ultimately built on, and it belongs in your file, not just the driller’s.

Do I have a water-right problem, or just a well?

On most single-family lots in Eastern Idaho you are drilling under the domestic exemption, which means you are not applying for a water right the way an irrigator does. That exemption has edges, and they moved recently.

Idaho Code 42-111 defines domestic purposes two ways. The first covers homes, camps, campgrounds and livestock, including irrigation of up to one-half acre of land, as long as total use does not exceed 13,000 gallons per day. The second covers any other purpose up to a diversion volume of 2.8 acre-feet per year. The statute also excludes mobile home parks, RV parks, multi-unit apartments and condos, and primarily commercial establishments from the first definition unless they fit the 2.8 acre-foot limit, and it bars stacking multiple domestic rights to supply a use that would not qualify as domestic on its own.

Two numbers to sit with. 13,000 gallons per day is enormous for a household: a family using 400 gallons a day is at roughly 3 percent of it. But one-half acre is not much irrigated landscape at all on a three-acre or five-acre parcel. If the plan is irrigated lawn across an acre, that is the limit you will bump into first, not the daily volume.

The other edge is subdivisions. The statute treats a tract divided into five or more lots as a subdivision, with an exception for agricultural divisions where lots are five acres or larger. The legislature amended this section in 2025 and again in 2026, tightening how the exemption applies to multi-lot developments, and plats filed before July 1, 2025 are generally treated under the older rules. In some groundwater management areas, domestic wells can be limited mainly to in-home household use and stock water, with outdoor irrigation requiring a permit.

What that means practically: if you bought a lot in a newer development and the seller told you “it has a domestic well right,” that is worth verifying against the current statute and the plat date rather than taking at face value. It is a title and water question, and it is one I would rather raise before you close than after.

What does the water system cost?

I will give you market figures here and label them as exactly that. These are published national cost ranges, not SwagerBuilds pricing, and not a quote for your lot. Well costs in particular swing wildly with depth and what the drill hits.

Component	Published market range	What moves it
Submersible well pump, installed	$1,000 to $2,500	Depth, horsepower, wire run
Pressure tank replacement	$500 to $1,000	Tank size
Constant-pressure system, installed	$2,000 to $5,000	Drive, pump, controls
Pressure switch	$25 to $100	Part only
Atmospheric storage tank, 300 to 500 gal	$250 to $500	Material, freeze protection
Atmospheric storage tank, 1,000 to 3,000 gal	$500 to $1,500	Size, burial vs above grade
Electrician labor	$50 to $130 per hour	Local rates, circuit run length

What is not in that table, and the part people forget: the well itself, the trench from the wellhead to the house at 42 inches of cover, the electrical service out to the well, the wellhouse or vault if the site needs one, the pressure regulator and expansion tank if static pressure runs high, and the mechanical room floor area that storage and a booster pump occupy.

On a rural lot, water and septic together are usually one of the three biggest line items outside the house itself. Our breakdown of well and septic cost in rural Idaho covers that side, and the items that catch people are collected in the hidden costs of building a custom home.

For the house itself, our published pricing is simple and does not change by component: on the Teton Valley and Idaho side, a SwagerBuilds custom home starts at $400 per square foot and goes up. On the Jackson Hole side it starts at $1,000 per square foot and goes up. Those are construction cost on conditioned square footage, and they are fixed price after design lock. Site work, utilities, permits and landscape sit on top, which is why we price them from real numbers for your lot rather than a per-square-foot guess. The full picture is in our honest cost to build in Teton Valley.

What do we lock down during design, and when?

This is the part that separates a house with good well water pressure from a house with an expensive problem, and it is all front-loaded.

SwagerBuilds runs the whole path here. We site the well against the setback math and the septic layout, coordinate the driller and the pump outfit, carry the engineering relationships for the site and septic design, and get the mechanical room drawn large enough for whatever the well turns out to need. You are not assembling a team of specialists on your own. That work happens under a design agreement with a fixed design fee, quoted per project, before any construction price gets signed.

The sequence we work to:

1. Lot review, before you close if possible. Setbacks, surface water, drilling-concern or management-area status, plat date and water-right language, neighboring well logs.
2. Well sited on the site plan. Not a dot placed last. It drives the house position when setbacks are tight.
3. Well drilled and tested early. Static level, pumping level and production rate on paper. Everything downstream waits on this number.
4. Water system designed to the tested yield. Pump sized under the well’s capacity, tank drawdown sized to the peak, storage and booster added if the yield is short, pressure setting chosen for the house’s height and run length.
5. Mechanical room sized and drawn. Tank, softener loop, water heater and any storage, with service clearance. A 120-gallon pressure tank and a 500-gallon storage tank do not fit in a closet.
6. Water tested, not assumed. Hardness, iron and manganese are not in the standard Idaho health panel and have to be requested by name. They determine the treatment train.
7. Trench and electrical coordinated. 42 inches of cover, pump circuit on the load calculation, conduit in before the site closes.

Step 3 is the one people want to skip to save a few thousand dollars early, and it is the single worst place to save money on a rural build. Until the well is tested you are guessing at your own well water pressure, and every guess downstream compounds. Where that fits in the overall order of operations is in our steps to building a custom home in Idaho, and what gets settled and paid for in the design phase is in the design phase explained.

If you are still choosing a lot, well yield belongs on your comparison list alongside views and access. We get into that on the best lots in Driggs, the best lots in Victor, and specifically on the valley’s west side in the Packsaddle trade-off. Getting a raw parcel ready to build is covered in how to prepare land to build a house, and the other rural-lot item that shares the same soil-and-gas conversation is in radon mitigation in a new Idaho home.

Two last cross-references, because they both hinge on flow and pressure: a tankless water heater needs a minimum flow rate to fire and is unforgiving of pressure swings, so it is a poor match for a marginal well without storage. And the mechanical room that holds all of this is the same room where whole house ventilation equipment lands, which is why we draw it once, early, with everything on it.

Frequently asked questions

What is normal well water pressure for a house?
Most modern well systems are set to either 30/50 or 40/60 psi, meaning the pump turns on at the lower number and off at the higher one. On a custom home I want 40/60. The figure that actually matters is flowing pressure at the highest and farthest fixture, where you want to hold roughly 20 psi while water is running. Dishwashers and washing machines need at least 10 psi at their inlet, and lawn sprinklers typically want 20 to 40 psi.

Why does my well water pressure drop when someone else turns on a faucet?
Usually one of three things. The pressure tank’s usable drawdown is too small, so the pump restarts under light demand and pressure dips while it catches up. The pump is undersized for the house’s peak demand, so simultaneous fixtures outrun it. Or the pipe from the well or through the house is too small, so friction loss eats the pressure before it reaches the fixture. A fourth possibility on an older system is a waterlogged tank that has lost its air charge.

How many gallons per minute does a well need for a house?
Five gallons per minute is the practical line where a normal household needs no supplemental storage. Below that you engineer around it with storage and a booster pump. Peak demand, not daily total, is what sets the target: published industry guidance puts a two-bathroom house at about 14 gpm and a three to four-bathroom house at about 17 gpm at the peak. A well under 0.5 gpm is generally not considered adequate for a home at all.

How deep does the water line from the well to the house have to be in Idaho?
At least 42 inches of cover. Idaho’s amendment to Section 609.1 of the Idaho State Plumbing Code replaces the national frost-depth language with a flat minimum: the cover over yard piping must be not less than 42 inches below grade. That is deeper than Teton County’s 32-inch frost depth, so the trench is dug to the plumbing rule rather than the frost rule.

Can I fix low well water pressure after the house is built?
Some of it, yes. A bigger pressure tank, a correctly set air charge, a pressure regulator, or a constant-pressure drive can all be retrofitted. What is hard and expensive to change later is a pump sized wrong for the well, undersized pipe buried in a 42-inch trench or inside finished walls, a mechanical room with no floor space for storage, and the well yield itself. That is why we test the well and design the system before the foundation goes in rather than after.

Want this settled before you buy the lot?

If you are looking at a parcel in Teton Valley, Eastern Idaho or on the Jackson side and you want to know what the water situation really is before you commit, call me at (208) 520-0636 or get in touch here. I would rather spend twenty minutes on your well logs and setbacks now than fix a pressure problem in a finished house.

Built different. Built right. Built by SwagerBuilds.

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.