If your lot is in Teton Valley, start with the custom home builder in Driggs guide for costs, permits and timelines, or the Tetonia custom home builder page if you are looking north, where we have West Ridge Ranch lots ready for 2027 builds. The Teton Valley page covers Victor and the whole valley.
TL;DR: A backup generator on a rural Idaho lot is not really about the average outage, because the average outage here is short. It is about the eight-hour February one that drops the well pump and the heat at the same time. Size it around the loads that fail badly, pick the transfer switch before the generator, and know that Idaho’s electrical code says almost nothing about any of it.
Contents
- Do you actually need a backup generator in Teton Valley?
- What a backup generator has to carry in a rural house
- Three ways to size a backup generator
- Manual switch, interlock kit, or automatic transfer switch?
- What Idaho’s electrical code says about generators, and what it skips
- Propane, natural gas, or diesel on a Teton Valley lot
- How long will a 500-gallon propane tank run a backup generator?
- Where the generator goes, and what it sounds like
- Is a battery better than a backup generator?
- What drives the cost
- How we handle backup power on a SwagerBuilds build
- Backup generator FAQ
Do you actually need a backup generator in Teton Valley?
Start with the honest number, because most backup generator sales pitches skip it. Fall River Rural Electric Cooperative, which serves most of Teton Valley, reports a 2022 average outage duration of 165 minutes per member, against an average of more than 500 minutes for Idaho electric utilities that year. Its own five-year figure for 2018 through 2022 is under 300 minutes per member, which it describes as a little over 24 minutes a month. The co-op runs 25 substations. By utility standards that is a good record, and it excludes major weather events and wholesale supply problems.
Nationally the picture is similar in shape. The U.S. Energy Information Administration reported that American customers averaged 11 hours without power in 2024, but nearly nine of those hours came from major event days, which is 80 percent of the total. Interruptions outside major events routinely average about two hours a year.
So the case for a backup generator is not the two hours. It is the tail. A handful of hours a year, concentrated in one or two bad storms, in a place where the storms land in January and the lots are at the end of long rural feeders. The question is not how often the power goes out. It is what breaks when it goes out for eight hours at ten degrees.
That is a different question for a house on a well than for a house in town, and it is why I treat a backup generator as a rural-lot decision rather than a luxury upgrade. If you are still choosing a parcel, it belongs in the same conversation as well and septic cost and the rest of what it takes to prepare land to build a house.
What a backup generator has to carry in a rural house
In town, an outage is an inconvenience. On a well, with no gas main, an outage takes your water, your heat, and sometimes your sewer in the same minute. That is the list worth protecting, and it is shorter than people expect.
The loads that actually matter in a cold-climate Idaho house:
- The well pump. No power, no water, and no water means no flushing and no refilling a boiler. Pump starting current is the single biggest surge most houses have. We cover pump and pressure-tank sizing in detail in will my well give the house enough water pressure.
- Heat. A gas furnace needs maybe 600 watts to run its blower and controls. A boiler needs its circulators. A heat pump needs real amperage, and a cold-climate heat pump needs it on exactly the night you are losing power.
- Freeze protection. This is the one that turns an outage into a claim. Pipes in an unheated bay, a hose bib, the slab edge in an unheated garage. A house that loses heat for a day in February can cost more to repair than the generator.
- A septic lift pump, if the lot needs one.
- Refrigeration, a few lights, internet, and the garage door. Small loads, high quality-of-life return.
- Fresh air and filtration. If the outage happens during smoke season, the whole house ventilation fan and the air filtration in front of it are worth keeping alive.
Notice what is not on that list: the range, the dryer, the hot tub, the car charger, and the second oven. Those are the loads that drive a generator from 14 kW to 26 kW, and they are the loads you can live without for eight hours. That single distinction is most of the sizing conversation.
Three ways to size a backup generator
There are only three honest approaches, and the one you choose decides the generator, the switch, and the fuel tank all at once.
| Approach | What it powers | Transfer equipment | What sets the size | Fits |
|---|---|---|---|---|
| Essential circuits | Well pump, heat, fridge, some lights and outlets, internet | Small manual or automatic switch feeding a subpanel | The well pump’s starting surge, plus the heating system | A house with a gas or propane furnace and a modest well; the lowest-cost path that still protects the house |
| Load-managed whole house | Everything, but not all at once. Electronics shed the big loads in sequence | Service-rated automatic switch plus load-management modules | The largest combination the controls will ever allow at one time | Most of the custom homes we build. You get normal life on a smaller machine |
| True whole house | Everything, simultaneously, with nothing managed | Service-rated automatic switch sized to the service | The full calculated load of the house | All-electric houses, heat pumps plus EV charging, or an owner who does not want to think about it |
Load management is the move most people should make and most people have never heard of. Instead of buying a generator big enough to start the heat pump, the oven, and the dryer in the same second, you buy a smaller one and let the controls decide the order. The dryer waits. Nobody notices.
Two things matter more than the kilowatt number on the lid. First, surge. A well pump or a compressor draws several times its running current for a moment at startup, so a generator that comfortably carries the running load can still stall on the start. Soft starters and electronic load control are often cheaper than the next size up. Second, derating for altitude. Teton Valley floor sits around 6,100 feet and the benches run higher. Naturally aspirated engines lose output with altitude, so a machine rated at sea level does not deliver its nameplate here. Ask your installer for the altitude-corrected rating in writing, not the brochure number.
Manual switch, interlock kit, or automatic transfer switch?
Pick the transfer equipment first. It decides how the house behaves at 2 a.m. when nobody is awake to notice the power went out, and it is the part that keeps a lineman safe.
Whatever you choose, the job is the same: it has to be impossible to connect the generator and the utility to the house at the same time. Backfeeding a de-energized line is how people get killed, and code treats that as the whole point of transfer equipment, not a feature of it. Never run a generator into a dryer outlet or a “suicide cord.” If a contractor offers that, you have learned something useful about the contractor.
| Option | How it works | Who acts | Watch out for |
|---|---|---|---|
| Generator interlock kit | A sliding plate in the main panel physically prevents the main breaker and a generator breaker from being on together | You, by hand: kill the main, start the generator, flip the generator breaker, then shed loads yourself | Must be a kit listed for that exact panel. You are the load management, so the discipline has to be yours |
| Manual transfer switch | A separate switch feeding a dedicated subpanel of chosen circuits | You, by hand, but the circuit selection is already decided and labeled | Only the circuits in that subpanel are covered. Decide them during design, not after drywall |
| Automatic transfer switch (load side) | Sits downstream of the service and switches a subpanel or the whole panel automatically within seconds | Nobody. It senses the outage, starts the generator, and transfers | Adds a box and a second set of conductors. Needs a maintained exercise schedule to stay reliable |
| Service-rated automatic transfer switch | Replaces the service disconnect, so utility power and generator power both land in one listed enclosure | Nobody | Cleanest install on new construction, but it has to be planned with the meter and service layout, not retrofitted later |
On a new build the service-rated automatic switch is usually the right answer, for an unglamorous reason: we are already setting the meter, the service conductors, and the panel, so making the transfer switch part of that assembly costs far less than adding it as a second enclosure after the fact. It also means the generator is sized and the panel is sized in the same conversation, which is the point of the electrical panel and service capacity discussion we have before the slab goes in.
One manufacturer detail worth knowing, because it changes the sizing math: an automatic switch can be told to lock out a single large load. Generac, for instance, lists an auxiliary transfer switch contact kit for exactly that, and notes it is not compatible with their 50-amp pre-wired switches. That one accessory sometimes saves a whole size class of backup generator.
What Idaho’s electrical code says about generators, and what it skips
This is the part nobody tells you, and it is the most useful thing in this post.
Idaho’s electrical rules live in IDAPA 24.39.10, the Rules of the Idaho Electrical Board, administered by the Idaho Division of Occupational and Professional Licenses. Section 600.01 adopts the 2023 National Electrical Code and then amends it, item by item, from (a) through (hh). That is 34 state amendments to the national code.
I read all 34. Not one of them mentions generators, standby power, or transfer switches.
That matters in both directions. It means Idaho has not softened anything about backup power, so NEC Article 702, which governs optional standby systems, applies to your house exactly as written. And it means the state has added no local requirement either: no mandated size, no required transfer switch type, no rule that a new rural house be generator-ready. The design is entirely your builder’s and your electrician’s call, which is also true of the filter in your furnace and, as we found earlier this month, of several other things Idaho leaves open.
Idaho’s amendments do touch the neighborhood of this work. Amendment (k) narrows arc-fault protection in one- and two-family dwellings to bedroom circuits only. Amendments (o) and (r) allow emergency disconnects on one- and two-family dwellings, which is relevant to how your service and a service-rated switch get arranged. Amendments (gg) and (hh) address energy storage: systems must be listed, except lead-acid batteries, and in one- and two-family dwellings the disconnect or its remote control must be readily accessible. If you are weighing a battery instead of a generator, those two are the Idaho-specific rules that apply to you.
From the national code, the one requirement that actually shapes your quote is the capacity rule. Under the 2023 NEC, if the generator picks up the load automatically, the system has to either supply the full load that gets automatically connected, or have capacity sufficient for the maximum load that an energy management system will connect. In plain terms: you may not wire an automatic switch to more house than the generator can carry and hope nobody runs the dryer. If you want a smaller generator on an automatic switch, the load shedding has to be engineered in, not left to the homeowner’s judgment. With a manual switch the user selects the loads, which is why interlock kits and manual switches are allowed to be simpler.
The permit side is specific and easy to get wrong. Under Section 500 of the same rule, electrical permits must be purchased before work commences, the permit holder must request an inspection, no wiring or equipment may be concealed from sight until it has been inspected, and a permit expires 365 days after purchase. The rule also sets an existing-dwelling-unit permit at sixty-five dollars per inspection. So if you are adding a backup generator to a house you already own, that is a permitted, inspected job with a published fee, not a weekend project. On a new build it folds into the electrical permit we are already pulling, and the generator circuit gets inspected along with everything else. What gets inspected and when is worth reading if you have not been through it.
Propane, natural gas, or diesel on a Teton Valley lot
Fuel choice is usually decided for you by the lot, not by preference.
Natural gas is the easiest fuel to live with, because the backup generator never needs refilling and there is no tank to site. It is also unavailable on most of the rural lots we build on. If a gas main runs to your parcel, use it.
Propane is the default for a rural Idaho custom home, and it has a quiet advantage: most of these backup generators make more power on propane than on natural gas. Generac’s published spec sheet for the 26 kW Guardian rates it at 22,500 watts on natural gas and 26,000 watts on propane. Same machine, same pad, 3.5 kW of difference. If you are sizing near a threshold, the fuel changes which side of it you land on.
Diesel makes sense when you need a big machine, a long unattended run, or a unit that is not dependent on a gas regulator in the cold. It costs more up front, needs the fuel kept fresh, and is the loudest of the three. For a house, propane usually wins.
Two propane details that get skipped on rural installs. First, the tank has to be sized for vaporization, not just for volume. A propane tank has to boil liquid into gas to feed the backup generator, and how fast it can do that depends on how much tank wall is in contact with liquid and how cold it is outside. A tank that holds plenty of fuel can still fail to deliver enough gas on a ten-degree morning if it is too small or too empty. That is why a backup generator on a Teton Valley lot gets a 500- or 1,000-gallon tank, not a pair of cylinders, and why your propane supplier should size the tank and the regulators for the backup generator’s peak demand in winter conditions. Second, plan the tank location with the driveway. A tank the truck cannot reach in February is a tank that does not get filled in February, which is the same month you will want it.
How long will a 500-gallon propane tank run a backup generator?
You can do this arithmetic yourself, and you should, because it is the number that tells you whether your plan survives a real storm.
From the same manufacturer spec sheet, the 26 kW Guardian burns 2.06 gallons of propane per hour at half load and 3.63 gallons per hour at full load. Propane tanks are filled to about 80 percent, so a 500-gallon tank holds roughly 400 usable gallons and a 1,000-gallon tank roughly 800.
| Tank | Usable propane (at 80%) | Runtime at half load | Runtime at full load |
|---|---|---|---|
| 500 gallon | about 400 gallons | about 194 hours, roughly 8 days | about 110 hours, roughly 4.5 days |
| 1,000 gallon | about 800 gallons | about 388 hours, roughly 16 days | about 220 hours, roughly 9 days |
Three honest caveats. That tank is also feeding your furnace, your water heater, your range and your fireplace, so backup generator runtime competes with heating. The tank is rarely full when the storm arrives. And a backup generator sized with load management spends most of an outage well under half load, which stretches those hours considerably. The point of the table is not the exact figure. It is that a correctly sized propane install buys you days, not hours, and that is a different category of protection from a portable unit and a gas can.
Multiply gallons per hour by your own delivered propane price to get the cost of running it. I am not going to publish a fuel price that will be wrong by spring.
Where the generator goes, and what it sounds like
Siting is a design decision, and on a snowy lot it is not a small one.
The manufacturer’s listing governs clearance. The 26 kW Guardian is listed and labeled for installation as close as 18 inches to a structure, and the spec sheet directs that it be located away from doors, windows and fresh air intakes and in accordance with local codes. Combustion engines make carbon monoxide, so that second sentence is the one that matters. Keep it away from openings, away from where the dog sleeps, and off the path of a bedroom window.
Noise is real but overstated. The same sheet lists 67 dB(A) at 23 feet under normal load, and 57 dB(A) at 23 feet during its low-speed weekly exercise. Conversation is around 60. Your neighbors will hear it on the one night it runs; you will barely hear the Tuesday self-test.
Then the Idaho part. The pad has to sit above where the snow piles and where the roof dumps, because a backup generator buried in a drift cannot get combustion air and an air-cooled unit that cannot breathe shuts down. Keep it out from under eaves that shed, which is the same reasoning behind how we detail roofs to prevent ice dams, and plan for the snow load the site actually gets. Leave yourself a path to shovel to it. And since the whole point is that it runs when you are not there, put it on monitoring, which is one of the few smart home features that pays for itself: a backup generator that failed its self-test in November and told nobody is not backup power.
Wildfire season adds one more reason to care. In smoke and fire conditions, utilities across the West de-energize lines on purpose, and that kind of outage is planned, regional, and long. If the lot is in that exposure, read this alongside how we approach a wildfire resistant home.
Is a battery better than a backup generator?
Sometimes, and it depends almost entirely on how long your outages are and whether the house is all-electric.
| Propane standby generator | Home battery | |
|---|---|---|
| Runtime | Days, limited by the tank | Hours for the whole house, longer on essential circuits only |
| Refuel | Propane truck | Grid, or solar if you have it and the sun is out |
| Cold weather | Runs; needs a correctly sized tank and a cold-weather kit | Capacity and charge rate drop in the cold unless the enclosure is conditioned |
| Startup surge | Handles a well pump well, especially on propane | Depends on the inverter rating; a deep well pump can be a problem |
| Noise and emissions | About 67 dB(A) at 23 feet; combustion, so siting matters | Silent, no exhaust, can sit in a garage |
| Maintenance | Oil, filters, a weekly exercise cycle, annual service | Essentially none, with a finite cycle life |
| Idaho code note | No state amendment addresses it; NEC 702 applies as written | Must be listed except lead-acid, and the disconnect must be readily accessible |
For a house on a well in Teton Valley, the backup generator is usually the better single answer, because a long winter outage is the scenario you are buying for and days beat hours. The combination is better still, and increasingly common on all-electric builds: battery for the quiet two-hour outages that make up most of the count, backup generator for the rare multi-day event. Just do not buy both to hedge a decision nobody has made yet. Pick the scenario first.
What drives the cost
I am not going to publish a backup generator price here, because the installed number swings more with site conditions than with the machine, and a stale figure is worse than none. What I can tell you is exactly what moves it:
- Backup generator size, which is driven by the sizing approach you chose above, not by the square footage of the house.
- Transfer equipment. An interlock kit is a fraction of a service-rated automatic transfer switch. This is usually the largest single swing.
- Load management modules, if you are going smaller on purpose.
- Fuel. Tank purchase or lease, the gas line, the regulator, and the excavation to set the tank where the truck can reach it.
- Distance. Trenching from the backup generator to the panel, priced by the foot, and rock makes it worse.
- The pad and the electrical work, including any service changes.
- Permit and inspection. Published and modest. Idaho’s rule sets an existing-dwelling-unit electrical permit at sixty-five dollars per inspection; on new construction it rides along with the electrical permit already in the budget.
The real lever is timing. Every one of those line items is cheaper while the trenches are open and the service is being set than it is after the driveway is poured. Making a house generator-ready during construction, a conduit stub, a pad location, the tank sized with the generator in mind, a transfer switch planned into the service, costs very little and preserves the option. Adding it in year three means opening ground twice.
For how pricing works on our side of it, SwagerBuilds starts at $400 per square foot and goes up in Teton Valley and eastern Idaho, and is priced per project in Jackson Hole, with a fixed design fee, starting at $25,000 and quoted per project. Backup power is scoped as part of the electrical package, not sold as an add-on after the fact. If you want the broader picture first, start with what it costs to build in Teton Valley.
How we handle backup power on a SwagerBuilds build
Twenty years in construction has taught me that the backup generator conversation always happens. The only variable is whether it happens during design, when it is cheap, or during the first February, when it is not.
So we raise it at the electrical walk, before the slab, in the same sitting as the panel and the service. I ask three questions. Is the lot on a well? Is the heat electric? And how long are you willing to be without water? Those three answers settle the sizing approach, and the sizing approach settles everything else. A propane house on a modest well with a gas furnace usually lands on a load-managed machine and a service-rated automatic switch. An all-electric house with a heat pump and a car charger lands bigger, or lands on load management plus a battery.
Then it gets built in. The pad gets located with the snow and the propane truck in mind, the conduit gets run while the ditch is open, the tank gets sized with the supplier for winter demand rather than for the generator’s brochure, and the transfer switch is part of the service assembly instead of a box bolted on later. The circuits that matter get labeled, so the house is documented rather than guessed at. And because I am involved in every phase of every build, the electrician, the propane supplier and the excavator are hearing the same plan from the same person rather than three versions of it. We also keep 24/7 cameras on every job, so you can watch the service and the pad go in from wherever you are, which matters to the clients who are managing a build from out of state.
If backup power never becomes a priority, you have lost almost nothing: a stub of conduit and a thoughtfully placed pad. That is the cheapest insurance on the whole electrical package. For how we work in general, see our process, and for the market itself, building in Teton Valley and building in Driggs.
Backup generator FAQ
What size backup generator do I need for a house on a well in Idaho?
It depends on the heating system and the pump, not the square footage. A propane- or gas-heated house protecting its well pump, heat, refrigeration and some lights is usually well served by a mid-size machine with load management. An all-electric house with a heat pump and an EV charger needs a larger unit or engineered load shedding. Get the altitude-corrected rating and the pump’s starting surge in writing before you sign anything.
Does Idaho require a permit to install a backup generator?
Yes. Idaho’s electrical rule requires that a permit be purchased before work commences, that the permit holder request an inspection, and that no wiring be concealed before it is inspected. The rule sets an existing-dwelling-unit permit at sixty-five dollars per inspection, and permits expire 365 days after purchase. On a new build it is part of the electrical permit already being pulled.
Do I need an automatic transfer switch, or is a manual one fine?
A manual switch or a listed interlock kit is fine if someone is reliably home to operate it and to keep the big loads off. An automatic switch is better for a second home, for a house with a well, or for anyone who does not want to be awake for the transfer. Under the 2023 NEC, an automatic system must either carry the full load it connects or use an energy management system sized for the maximum load it will connect, so you cannot quietly undersize an automatic install.
How long can a backup generator run on a 500-gallon propane tank?
Roughly eight days at half load and about four and a half days at full load, using a 26 kW unit’s published consumption of 2.06 and 3.63 gallons per hour and a tank filled to about 80 percent. In practice the propane is shared with the furnace and water heater, and the tank is rarely full, so treat it as a planning estimate.
Should I put in a battery instead of a backup generator?
If your outages are short and the house is all-electric with solar, a battery can cover most of them silently and with no maintenance. If you are on a well in a cold valley and worried about a multi-day winter storm, the generator is the better single answer because its runtime is measured in days. In Idaho, energy storage systems must be listed, except lead-acid, and the disconnect or its remote control must be readily accessible in a one- or two-family dwelling.
Talk it through before the slab
If you are planning a custom home on a rural lot in Teton Valley or eastern Idaho, the backup power decision is cheapest right now, before the service is set and the ground is closed. Call me at (208) 520-0636 or use the contact page and we will walk the loads, the fuel and the switch together.
Built different. Built right. Built by SwagerBuilds.