Pick a backup generator by totaling your essential appliances’ running watts, adding the largest starting surge, then decide portable or standby.
When the power goes out, a generator either keeps the circuits you need running or wastes fuel on everything you don’t. Sizing comes before shopping. Choosing a backup generator comes down to three decisions: how many watts your essentials require, whether a portable or standby unit fits your property, and how the generator connects safely to your electrical panel.
Sizing A Home Backup Generator: Running Watts And Surge Watts
Size a generator from the loads you need during an outage, not from the biggest model in the store. Running watts are the steady electricity an appliance uses once operating. Starting watts (surge watts) are the extra power a motor or compressor draws for a few seconds when it kicks on—refrigerators, well pumps, and sump pumps all need that startup kick.
Make a list of circuits that genuinely matter during an outage:
- Refrigerator and freezer
- Well pump or sump pump
- Furnace fan or boiler circulator
- Lights, internet, and phone charging
- Medical equipment or a home office setup
Add the running watts for everything on your list, then add the single largest starting surge. Motors rarely start simultaneously, so planning for one big surge at a time is realistic. Leave a modest buffer above the total so the unit isn’t straining at maximum output for hours. Consumer Reports’ generator sizing guide recommends the same method: list appliances, add their wattages, and factor in how often and how long outages usually last in your area.
Portable Or Standby: Which Fits Your Home?
Choose a portable generator for lower upfront cost and occasional, shorter outages. Choose a home standby generator when outages are frequent, long, or you want backup power to come on automatically without going outside.
| Factor | Portable Generator | Home Standby Generator |
|---|---|---|
| Startup | You wheel it outside, connect it, and pull the start | Turns on automatically when utility power drops |
| Fuel | Gasoline or propane tanks you refill and store | Permanent natural gas or propane hookup, so long runs need no refilling |
| Connection | Extension cords, or a transfer switch or interlock | Hardwired into a transfer switch tied to your panel |
| Installation | None, though a transfer switch needs an electrician | Licensed electrician and local permit typically required |
| Upfront cost | Lower | Higher |
| Best match | Occasional outages and a handful of essential circuits | Whole-home or selected-circuit automatic backup |
Fuel availability often settles the portable-versus-standby question. Natural gas usually survives a local outage, but a portable generator cannot safely tap into a gas line—that option belongs to a standby unit. Propane stores well for portable use, and gasoline needs fresh stock rotated through the tank.
Voltage matters as much as wattage. Most US homes run on 120/240-volt split-phase service, so if a well pump, electric water heater, or central air conditioner is on your essential list, the generator and transfer equipment must supply 240 volts.
Once you know the class you need, comparing models is the last step—start with the models we’ve tested for home backup generators before shopping by price alone.
Wiring It Right: Transfer Switches And Generator Placement
Never connect a generator through a wall outlet or improvised panel hookup. Backfeeding sends power out through utility lines and can injure or kill a lineworker restoring service blocks away. A transfer switch or panel interlock listed for your breaker box separates generator power from utility power so the two can never collide.
Even a single circuit deserves a proper connection. Generac’s single-load manual transfer switch owner’s manual documents a common setup: the switch feeds one dedicated circuit, like a furnace or refrigerator, directly from the generator. Larger whole-home transfer switches cover multiple circuits, and installation guidelines spell out service-panel requirements. Most permanent connections need a licensed electrician and must satisfy local electrical code plus manufacturer’s instructions.
Placement is part of safety. Portable generators run only outdoors, positioned away from windows, doors, and vents, because engine exhaust is carbon monoxide. Noise, fuel storage, and maintenance also affect real-world satisfaction. A bigger unit is not automatically better—oversizing wastes fuel and adds cost. When you can name the circuits you need, the fuel that will feed the unit for a typical outage, and the transfer method your panel allows, you have everything required to pick the right generator.
FAQs
Can one generator power my entire house?
Only if the total running watts of everything you want to run at once stays under the generator’s output, and the transfer switch is sized for your electrical service. Most homeowners find powering selected essential circuits far more affordable, keeping the refrigerator, heat, and lights working through the same outage.
Why can’t I plug a portable generator into a wall outlet?
Power flows backward through the outlet and into the home’s wiring, then out onto utility lines. That backfeed creates a fire risk, can damage the generator, and puts electric workers at risk of electrocution. A transfer switch or listed interlock is the only safe way to connect to household wiring.
Are home standby generators worth the extra cost?
They pay for themselves when outages are frequent, long, or dangerous, since they start automatically and run on natural gas or large propane supply. If outages are rare and short, a portable generator at a fraction of the cost handles the same essential loads with a little manual effort.
References & Sources
- Consumer Reports. “How to Choose the Right Size Generator.” Explains listing appliance wattages and factoring in outage frequency and duration.
- Generac. “Single Load Manual Transfer Switch Owner’s Manual.” Documents connecting one dedicated circuit to a portable generator through a listed transfer switch.
- Fine Homebuilding. “Advice for Choosing and Using a Backup Generator.” Provides practical guidance on generator selection, placement, and safe home connection.
