Whole Home Standby vs Portable + Transfer Switch 2026 Black Hills Electrical Guide

Two homes on the same road can lose power in the same storm and have completely different weeks. One of them has a unit outside that starts by itself within seconds of the power dropping. The other has a generator in the garage, a gas can, and a decision to make about which breakers stay on. Here is what each one actually costs, what each one can actually carry, and how to run the numbers yourself before you call anybody.

Start with what the grid here actually does

Backup power gets sold with scary numbers, so it is worth being straight about ours. Statewide, South Dakota is one of the most reliable places in the country to be a utility customer. The U.S. Energy Information Administration found that customers in South Dakota, North Dakota, Arizona and Massachusetts averaged under two hours of service interruption for all of 2024. If you are buying a generator because you expect the lights to flicker every other week, that is not the Black Hills.

The case for backup power here is not the average. It is the tail.

In November 2025, a regional transmission event outside the local system took down the entire Black Hills Energy customer network, more than 77,000 customers, from roughly 1:40 p.m. to 8:30 p.m. That one was an inconvenience. Six weeks later a record wind event hit the Hills and it was a different animal. Black Hills Energy reported over 25,000 customers out, with nearly 11,000 still dark the following evening, while Black Hills Electric Cooperative had more than three quarters of its rural network down. Days later, roughly 2,000 customers were still without power, and utility officials described the infrastructure damage as the worst since Winter Storm Atlas in 2013.

So the honest framing is this: you are not buying protection from a flickering grid. You are buying a plan for the three to five day winter event that shows up every few years, when the roads are blocked, crews are coming in from other states, and your furnace, your well pump and your pipes do not care whose fault it is.

Two real options, and the names matter

There is a lot of loose language around this, including from people selling it. There are two genuinely different products.

1. A standby generator, also called a whole home generator

A permanently installed unit on a pad outside the house, hard piped to natural gas or propane, wired to an automatic transfer switch at the service. It monitors utility voltage, starts itself when the power drops, transfers the load, and shuts down and transfers back when utility power returns. It exercises itself on a schedule. You do not have to be home. You do not have to touch anything.

2. A portable generator connected through a transfer switch or an interlock kit

The unit you would recognize from a jobsite. Gasoline, or dual fuel on propane, wheels, a pull cord or an electric start. It gets connected to the house through a code compliant piece of equipment so that generator power and utility power can never be present at the same time. You start it, you fuel it, you shut it down, and you decide what stays on.

What a whole home standby generator costs installed

National installed pricing for a residential standby system generally lands between $6,000 and $11,000 for a typical home, with the equipment itself running $3,000 to $6,000 and labor $3,000 to $5,000. Larger units and difficult sites push higher. One installer breakdown puts the range at $7,000 to $20,000, with most 22kW whole home installs landing at $10,000 to $14,000. Angi puts the standby installation portion alone at an average of about $4,520, covering permits, assembly, placement and wiring.

Rather than argue about the total, look at what the total is made of. This is where quotes actually differ.

These are national planning ranges pulled from published cost data, not a Wires R Us quote. Every one of these lines changes based on what we see when we walk your property.

Two things worth flagging early, because they are the most common surprises. First, if your service is a tired 100A panel, a service upgrade or a panel swap may need to happen first, and that is a real cost that has nothing to do with the generator. Second, if there is no natural gas at your address, which is common outside the city limits, you are looking at a propane tank sized for multi day runtime, and that changes both the install cost and the operating math.

What a portable generator plus a transfer switch costs installed

This path is genuinely cheaper, and anyone who tells you otherwise is selling. Portable units themselves run roughly $500 to $2,500, with the useful 7,500W to 12,500W range mostly landing in the middle of that. The connection work is the part that needs a licensed electrician and a permit.

One cost calculator pegs the single most common configuration in American homes, a 10 circuit manual transfer switch paired with a 7,500W to 12,500W portable, at $1,400 to $2,000 turnkey.

Interlock kit or manual transfer switch

Both solve the same safety problem and both are legitimate. They solve it differently, and the difference shows up in how you live with it.

Interlock kits are listed for a specific panel brand and series, and roughly seven in ten residential panels have a compatible factory kit available. If you do not know what is on your wall, this rundown of the panel types found in homes is a good place to start. Some older panels have no listed kit at all, which pushes you toward a transfer switch or a panel swap.

What a portable can realistically carry

This is where the comparison stops being about money. Motor loads draw far more to start than to run, and that surge is what decides whether your generator carries the house or trips.

Ranges compiled from published appliance wattage data, including manufacturer sizing guidance and appliance load tables. Check the nameplate on your own equipment. These are planning numbers.

Run a realistic Black Hills winter list on a 7,500W portable. Furnace blower at 700, refrigerator at 300, freezer at 300, well pump at 900, lights and electronics at 500. That is 2,700 running watts, which sounds like plenty of headroom. Then the well pump kicks on while the furnace is already running and you are briefly asking for 2,700 plus a 2,500 watt surge. You are still fine. Now add a microwave and a space heater and you are hunting for the breaker in the dark.

What does not fit on a 7,500W unit: central air conditioning plus much of anything else, an electric dryer while the well is running, or an electric water heater at all. Published guidance is consistent that a 7,500W generator can cover essentials and one significant motor load, and that an electric dryer or a central air condenser will overload it if you stack them on top of the essentials. If you want central air during an outage, plan on 10,000 watts or more, and at that point you are into the largest portables and the price gap starts closing.

How to estimate this yourself before you call anyone

You should be able to walk into a quote with your own number. Here is how we would do it if we were you.

Sizing a portable

1. Write down only what runs at the same time. Not everything you own. The furnace, the fridge, the freezer, the well, the lights, one small kitchen appliance.
2. Add the running watts. Use nameplates where you can, the table above where you cannot.
3. Add the single largest starting surge, once. Two big motors starting in the same instant is possible but planning for it makes you buy a generator you do not need. Size for the biggest one.
4. Target 80 percent of the generator’s running rating, not the starting rating. The big number on the box is surge. The number that matters is continuous.
5. Check the 240 volt loads separately. A well pump or a furnace on 240V needs the generator to actually have a 240V outlet with enough capacity on that leg, which not every portable does.

Sizing a standby

This one is code driven, and that is a good thing because it means there is a defensible answer instead of a sales number. NEC Article 702 governs optional standby systems, and 702.4 requires that the system either have capacity for all the loads it is intended to serve, or that automatic load management equipment prevents overload. In practice there are three legitimate paths:

• Full Article 220 load calculation. Square footage, appliance nameplates, demand factors. It is the most conservative and usually produces the biggest generator.
• Historical peak demand. If the house exists and has a smart meter, twelve months of actual interval data gives you the real peak the house has ever pulled. This is almost always a much smaller number than the Article 220 result, and it is a recognized method. It does not work on a house that has not been built yet.
• Automatic transfer switch with load management. Load management under Article 750 lets a smaller generator legally serve a whole home, because the system sheds the air conditioning or water heater before the generator sees the load. This is how a 22kW unit legitimately covers a house whose calculated load says otherwise.

The single most expensive mistake homeowners make is sizing the generator to match the panel. A 200A service at 240V is 48,000 watts on paper. No house draws that. Matching the panel buys you a generator two sizes too big, and an oversized unit that never sees 50 percent load has its own problems with carbon and deposits.

The Black Hills number that is not in any online calculator

Every nameplate rating on every generator sold is a sea level number. Air gets thinner as you go up, combustion suffers, and the unit makes less power. Manufacturer spec sheets for air cooled home standby units state it plainly: maximum power decreases approximately 3.5 percent for each 1,000 feet above sea level, and roughly another 1 percent for each 10 degrees F above the rated ambient temperature.

Now apply that here. Downtown Rapid City sits at about 3,202 feet. Deadwood starts around 4,531 feet and climbs from there, and Lead is higher still.

Derate figures calculated from the published 3.5 percent per 1,000 feet factor. Elevations are approximate town center figures and vary considerably by lot, especially in the northern Hills. Confirm the actual site elevation and the manufacturer’s own derate curve for the specific model before sizing.

This is not a rounding error. A homeowner in Lead who sizes off an online calculator and buys a 22kW unit is buying something closer to 18kW of real capacity, and if the load calculation said 20kW, that system is going to trip on a January evening with the furnace and the well both calling. This applies to portables too, at roughly 3 percent per 1,000 feet. It is one of the reasons we do not quote generator sizes off a phone call.

Fuel and runtime, which is where the paths really separate

The purchase price is a one time conversation. Fuel is the conversation you have on day three.

Natural gas standby

If you have natural gas at the property, runtime is effectively unlimited as long as utility gas pressure holds. There is nothing to refill and nothing to store. This is the best case scenario and it is why natural gas units dominate in town.

Propane standby

Common outside the city limits, and it is a tank sizing question. A 500 gallon tank is filled to 80 percent under NFPA 58, so about 400 usable gallons. A 22kW unit at a realistic 50 percent household load burns roughly 1.8 to 2.0 gallons per hour, which works out to somewhere around 8 days of continuous runtime on a 500 gallon tank. Shut it down overnight and that stretches considerably. Most homes average well below 50 percent load during an outage, so real world runtime is usually better than the arithmetic suggests. The thing to plan for is that during a widespread outage, propane delivery gets delayed too.

Portable gasoline

A 7,500W portable with a 6 to 8 gallon tank runs roughly 10 to 12 hours at 50 percent load, and 6 to 8 hours at full load. Do the math on a five day outage. That is somewhere between ten and twenty refuels, in December, in the dark, with stations that may be down themselves and pumps that need power to run. You also need to have stabilized fuel on hand before the storm, because you will not be buying it during.

Our honest read on the tradeoff

There is a popular version of this argument that goes: you are already paying for a transfer switch and you already have to pick and choose what stays powered, so you might as well go whole home and stop thinking about it. We understand the appeal. We do not think the cost half of that argument holds up, and we would rather tell you that than win a sale with math that does not survive a calculator.

The transfer switch is not where the money is. An interlock or a manual switch is a few hundred to a couple thousand dollars, which is somewhere around ten to twenty percent of a standby install. A portable plus a compliant connection lands around $1,300 to $4,500. A standby system lands around $7,000 to $18,000. That is not a small step up you might as well take. That is a real decision with real money in it, and pretending otherwise insults your intelligence.

The portable path is genuinely the right call if

• Your outages are usually hours, not days
• Someone is home during most of the year
• You are on city water and gas heat, so your critical loads are small and manageable
• You are comfortable working a panel correctly, every time, under stress
• The budget is the constraint and something is better than nothing, which it absolutely is

Skip straight to standby if

• You are on a private well. No power means no water, and no water in winter starts a different set of problems
• Your heat depends on electricity to run, and a multi day loss means frozen pipes rather than a cold night
• Anyone in the house depends on medical equipment
• You travel, or you are gone for stretches in winter
• You work from home and an outage costs you income
• You are building. More on that below

The frozen pipe point deserves its own sentence, because it is the one that changes the arithmetic. A generator is expensive. A house that loses heat for three days in January in the northern Hills is a claim, a restoration crew, and months of your life. That risk is not evenly distributed across our service area, and it is a bigger deal in Lead and Deadwood than it is in Rapid Valley.

If you are building, the timing is the whole game

The cheapest generator install is the one that happens while the walls are open and the yard is already torn up. During construction, the pad location, the gas stub, the conduit run, the transfer switch location and the load calculation all get handled once, in coordination with the other trades, with no demolition and no restoration. Retrofit means trenching a finished lawn, working around a finished driveway, and sometimes re-doing gas pipe sizing that was never intended to carry a generator.

Even if a generator is not in this year’s budget, roughing in for one during the build is inexpensive insurance. A conduit and a gas stub to a future pad location costs a fraction of what it costs to add them in five years. We do a lot of new construction electrical for builders across the Black Hills, and this is one of the easiest conversations to have early and one of the most expensive to have late.

Frequently asked questions

Is a whole house generator worth it?

It depends almost entirely on your critical loads and how long your outages last, not on how much you dislike being inconvenienced. If you are on a private well, heat with something that needs electricity, or cannot be home reliably, a standby system solves a problem a portable cannot. If you have city water, gas heat and someone home, a portable and a properly installed interlock covers the same outage for a quarter of the money. Resale is sometimes cited as a justification. Treat that as a bonus, not a reason.

Is an interlock kit or a transfer switch better for a portable generator?

An interlock kit is cheaper, installs faster, uses your existing panel, and lets you reach any circuit in the house. The tradeoff is that managing the load is on you, and the kit has to be listed for your specific panel brand and series. A manual transfer switch costs more, limits you to the circuits it was wired for, and makes overloading nearly impossible because those are the only circuits available. Interlock for flexibility and price, transfer switch for simplicity under stress.

What size generator do I need for a whole house?

Most homes land somewhere between 14kW and 22kW, but the honest answer is that it comes from a load calculation, not a square footage rule of thumb. NEC Article 702 requires either full capacity for the loads served or automatic load management to prevent overload, and there are three legitimate ways to get there: an Article 220 calculation, twelve months of actual metered peak demand, or a smaller generator paired with a load management transfer switch. In the Black Hills you then have to derate for elevation, which most calculators do not do.

What will a 7,500 watt generator actually run?

Essentials plus one significant motor load. A gas furnace blower, a refrigerator, a freezer, a well pump, lights and electronics fit comfortably with headroom for surge. What does not fit is central air conditioning, an electric dryer, or an electric water heater stacked on top of that. If you want central air during an outage, plan on 10,000 watts or more.

Can I just plug my generator into my dryer outlet?

No. A double male cord energizes your panel and your service drop, which puts utility line workers at risk of electrocution and backfeeds through your main breaker with nothing protecting it. It also has no way to prevent utility power and generator power meeting. Interlock kits and transfer switches exist to make this physically impossible, and both cost less than the liability of the alternative.

How much does it cost to install a whole house generator?

Published national ranges put a complete residential standby install between roughly $6,000 and $20,000, with most typical homes landing in the $10,000 to $14,000 area for a 22kW system. The largest swing factors are the distance from the pad to your service and gas meter, whether natural gas is available at your address, and whether your existing service needs upgrading first. Get a line itemized quote so you can see which of those is driving your number.

Do I need a permit to install a generator or a transfer switch?

Yes, for both paths. Generator installs involve permitted electrical work and, on a standby unit, permitted gas work as well. Interlock kits and manual transfer switches are permitted electrical work too. Any contractor who tells you no permit is required is telling you something useful about how they operate.

Will a generator protect my electronics when the power comes back?

Not by itself. Utility restoration after a major storm is a common source of voltage surges, and a transfer switch handing the load back to the grid does nothing to filter that. That is a separate piece of equipment. We wrote about whole home surge protection and management if you want the detail.

Where to go from here

If you want to talk through your specific situation, our generator installation page covers what our process looks like, and we serve homeowners and builders across the Black Hills. If you are still deciding between backup power options in general, our solar, EV and generator overview lays out how these systems relate to each other.

And if the reason you are reading this is that a breaker keeps tripping and you are wondering whether a generator is even the right conversation, it probably is not. Start with why a bigger breaker is not the answer instead.