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What Size Whole-Home Generator Do You Need?

The right generator keeps what matters running when the power goes out, without paying for capacity you will never use. Here is how the sizing actually works.

Quick Answer

Generator sizing comes down to one question: what do you want running when the power is out? A smaller unit covers essentials like heating, the well pump, the refrigerator, and some lights and outlets. A whole-home system runs everything including central air. Most Valley homes land in between. The loads that drive the size are the big ones: central HVAC, the well pump, and any electric range or water heater. Callison assesses your home, recommends the size, and handles the transfer switch, panel work, and permits. Call 540-294-3189.

Outages in Augusta County are usually short and occasionally are not. Ice storms, summer thunderstorms, and wind events take lines down across Staunton, Waynesboro, and Fishersville most years, and homes on well water discover something that town-water homes do not: no power means no water either. Not for drinking, not for flushing.

That is usually what moves a standby generator from a nice idea to a decision. The next question is how big, and it is worth understanding before anyone quotes you, because the size sets the price more than any other factor.

Essentials, Middle Ground, or Whole Home

Coverage levelTypically runsDoes not runSuits
EssentialsHeating controls, well pump, refrigerator, some lights and outlets, internetCentral air, electric range, electric water heaterShort outages; keeping the house safe and habitable
Essentials plusThe above, plus selected larger circuits such as the water heater or one HVAC systemSimultaneous heavy loadsMost Valley homes
Whole homeEverything, including central air conditioningNothing, by designLonger outages; working from home; medical equipment

Most homeowners assume they need the top row and discover during the assessment that the middle one covers everything they actually cared about. That is the conversation worth having before you buy.

The Loads That Actually Drive the Size

Lights and outlets barely register. The size is set by a short list of heavy consumers, and if you know which of these you have, you already know roughly where you will land.

  • Central heating and cooling. Usually the single largest load, and the one that most often decides between the middle and top rows.
  • The well pump. Modest while running, but it draws a substantial surge at startup, and that surge has to be available.
  • An electric range or oven. Large, though you can choose to cook differently for a day.
  • An electric water heater. Large and, unlike the range, one people are unwilling to go without for long.
  • An EV charger. Very large. Almost always excluded from generator coverage, and load management can hold it off automatically.
  • A sump pump. Small draw, but if you have one, losing it during the storm that caused the outage defeats the purpose.

That surge point on motors is the one homeowners underestimate. A well pump, a submersible pump, or an air conditioner compressor draws several times its running load for the moment it starts. A generator sized only for running loads will stall when the pump kicks in, which is precisely when you need it.

Undersizing and Oversizing Both Cost You

There is a temptation to buy the largest unit available on the theory that more is safer. It is not that simple in either direction.

Undersized is the obvious failure. The generator runs, then something large starts, and it trips or stalls. You discover this during an ice storm rather than during the sales conversation.

Oversized is the quieter waste. You pay more up front for capacity you never use, the unit occupies more space, and it consumes fuel to produce power nothing is drawing. On propane, that difference across a multi-day outage is real, and it is the kind of thing nobody mentions until you are refilling the tank.

The right answer is the one that matches your actual loads with sensible headroom for motor startup, which is what the assessment establishes.

The Transfer Switch, and Why It Is Not Optional

A standby generator ties into your electrical system through a transfer switch, which disconnects the house from the utility before connecting it to the generator.

This is a safety device rather than a convenience. Without proper isolation, a running generator can push power back onto the utility lines, which is genuinely dangerous for the crews working to restore service. It is why this work is permitted and inspected, and it is why a standby generator is not a homeowner installation.

The switch also determines what actually gets backed up. A whole-house switch covers everything downstream of it. A subpanel arrangement backs up a selected set of circuits, which is frequently the more economical route and is how most essentials and essentials-plus installations are built. Which one suits you interacts with your existing panel capacity, so the two get assessed together.

Automatic Operation and What Ownership Involves

A standby generator starts on its own within seconds of an outage and shuts down when utility power returns. You do not need to be home, and you do not need to do anything. That is the entire difference between a standby unit and a portable one you drag out of the garage in the rain and refuel by hand at three in the morning.

Two things worth knowing before you own one. It will exercise itself on a schedule, running briefly every week or two to keep the engine healthy, and you will hear it. Neighbors sometimes have opinions, so placement is worth thinking about.

And it is an engine, so it needs servicing on a schedule like any other. A generator that has not been maintained is a generator that may not start on the day it matters, which is the failure mode that stings most given what one costs.

Standby or Portable?

Before sizing anything, it is worth being honest about whether you need a standby unit at all, because for some households a portable generator is a reasonable answer and costs a fraction as much.

A portable makes sense if outages at your address are rare and brief, you are usually home when they happen, you are physically able to move and refuel it, and you can live with running a few appliances on extension cords. It has to be run outdoors, well away from the house and never in a garage even with the door open, because the exhaust is the real hazard rather than the fuel.

A standby unit earns its cost when you are on a well, when someone in the house depends on powered medical equipment, when you work from home and an outage costs you a day, when outages at your address regularly run past a few hours, or simply when nobody is going to be around to wrestle a portable into place at two in the morning in an ice storm.

Fuel and Placement

Standby generators typically run on natural gas or propane, and which is available at your property is often the first thing that narrows the options. Natural gas draws from the utility supply continuously. Propane comes from a tank, so tank size determines how long you can run, and it is worth sizing that against a realistic worst case rather than a typical one.

Placement is governed by clearance requirements from windows, doors, and vents, because the unit produces exhaust. There is usually a sensible spot on any property, but it constrains where the gas supply and the electrical run have to reach, and that affects installation cost. It is one of the reasons a site visit gives you a real number where a phone call gives you a range. Distance from the panel and from the gas supply are usually the two variables that move installation cost most, and neither is something anyone can estimate without standing at the property.

On a well? Prioritize the well pump. Homes on well water lose running water the moment the power goes out, and that single circuit is usually the difference between an outage being an inconvenience and being a real problem. See our generator installation page.

Why Augusta County Homeowners Call Callison

Callison Electric Heating & Cooling has been family owned in Staunton since 2003, and a generator project is exactly the kind of work where holding both licenses matters. The sizing depends on your HVAC load, and the installation is electrical work. We do both.

We add up what you actually want running, size the unit to that with proper headroom for motor startup, and handle the transfer switch, the panel work, and the permits as a single project rather than coordinating across trades.

  • Family owned in Staunton since 2003
  • VA Class A dual license, electrical and HVAC, #2705111964
  • BBB Accredited with an A+ rating
  • Sized to your real loads, including motor startup surge, rather than sold by catalog
  • Transfer switch, panel work, and permits handled as one project
  • Work left inspected and to code
  • 1-year workmanship warranty on every job
  • Upfront pricing, quoted and approved before anything starts
  • Same-day service available when you call before noon, plus weekend emergency calls
  • Financing available on qualifying work

We serve Staunton, Waynesboro, Fishersville, Stuarts Draft, Verona, and all of Augusta County. See the full range on our electrical services page.

Want the Right-Sized Generator in Staunton or Augusta County?

We walk the house, add up what you actually want running, and recommend a size that covers it without paying for capacity you will never use. Quoted up front, permits included.

Answers

Common questions

Real questions from Staunton and Augusta County, with straight answers.

Call 540-294-3189
What size generator do I need for my house?
It depends on what you want running. A smaller unit covers essentials like heat, the well pump, and the refrigerator; a whole-home system runs everything including central air. The size is driven by the big loads, not by lights and outlets. Callison sizes it to your actual loads.
Why does a well pump matter so much for generator sizing?
Because it draws a large surge at startup. A pump pulls several times its running load for the moment it starts, and a generator sized only for running loads will stall right when you need it. Homes on wells also lose all running water during an outage.
Does a whole-home generator turn on automatically?
Yes. A standby generator starts on its own within seconds of an outage and shuts down when utility power returns, with no action needed from you. That is the main practical difference from a portable unit you refuel by hand.
Is a bigger generator always better?
No. Undersized means it stalls when something large starts. Oversized means paying up front for capacity you never use and burning fuel to produce power nothing is drawing, which matters on propane during a multi-day outage. Match the real loads with sensible headroom.
What is a transfer switch and do I need one?
It disconnects your home from the utility before connecting the generator, and yes, it is required. Without proper isolation a running generator can backfeed the utility lines and endanger the crews restoring power. It is why this work is permitted and inspected.
Does a standby generator need maintenance?
Yes, it is an engine. It also exercises itself briefly every week or two to stay healthy, which you will hear, so placement is worth considering. An unmaintained generator may not start on the day it matters, which is the failure that stings most.
Does Callison handle the permits and electrical work?
Yes. Callison is a licensed electrician serving Staunton, Waynesboro, Fishersville, Stuarts Draft, Verona, and Augusta County, and handles the transfer switch, panel work, and permits as a single project rather than coordinating across trades. The work is left inspected and to code, and it is quoted up front so you approve the price before anything starts. Call 540-294-3189.