A standby generator is only as good as its sizing. Too small, and it can’t run what you need during an outage; too large, and you’ve overpaid for capacity you’ll never use. As an authorized Generac dealer, sizing generators correctly is something we do week in and week out — so let’s make it simple.
Storm season in the Eastern Panhandle makes backup power more than a convenience. Here’s how to figure out the right size for your home.
First decide: essentials or whole home?
The single biggest factor in sizing is what you want to keep running. There are two common approaches:
- Essential circuits — refrigerator, furnace blower, well or sump pump, a few lights, and outlets. This keeps your home livable on a smaller, more affordable unit.
- Whole home — everything, including central air conditioning. This needs a larger generator but means an outage barely changes your daily routine.
How generator sizing actually works
Generators are rated in kilowatts (kW). Sizing isn’t just adding up your appliances — it has to account for the surge of power that motors draw when they start. An air conditioner or well pump can pull several times its running wattage for a split second at startup, and the generator has to handle that spike.
That’s why proper sizing is done by a professional with a load calculation, not by guesswork. We measure or calculate your home’s actual demand, factor in those startup surges, and recommend a unit with the right headroom — no more, no less.
Fuel matters: natural gas vs. propane
Standby generators typically run on natural gas or propane. Natural gas connects to your existing supply, so runtime is essentially unlimited during an outage. Propane requires a tank, and runtime depends on tank size. Your available fuel source can influence which generator and configuration make the most sense.
Don’t forget the transfer switch
A standby generator connects to your home through an automatic transfer switch, which detects an outage and switches your home to generator power within seconds — then back when the grid returns. It also prevents backfeeding power onto utility lines, which is a serious safety hazard. The transfer switch is not optional, and it must be installed by a licensed electrician.
Why professional installation pays off
A correctly sized, professionally installed generator starts reliably when you need it and runs safely for years. As a Generac dealer, we handle sizing, placement, the gas connection, the transfer switch, the permit, and ongoing maintenance — so your backup power is ready the moment the lights go out.
Frequently Asked Questions
What size generator runs a whole house?
It depends on your home’s size and whether you’re running central air. Whole-home coverage typically needs a larger unit — we confirm the exact size with a load calculation rather than a rule of thumb.
How long can a standby generator run?
On natural gas, it can run for days because it draws from your gas line. On propane, runtime depends on tank size. Either way, standby units are built to run for extended outages.
Do I need an electrician to install a generator?
Yes. The transfer switch and electrical connection must be installed by a licensed electrician, and the project requires a permit and inspection — all of which we handle.