Choosing the right whole-home generator comes down to four things: how much power you actually need to keep running during an outage, what fuel source makes sense for your property, the difference between a standby generator and a portable one, and making sure the installation meets local code requirements. Getting these decisions right upfront saves you from buying either more generator than you need or not enough to cover the loads that matter most.

Standby vs. Portable: Which Type Is Right for You?

Portable generators are less expensive upfront, but they require manual setup, need to be refueled with gasoline, must be operated outdoors to avoid carbon monoxide poisoning, and can only power a portion of your home through extension cords or a transfer switch. Standby generators are permanently installed outside your home, connected to your natural gas or propane supply, and wired directly to your electrical system through an automatic transfer switch. When utility power fails, a standby generator detects the outage and starts itself within seconds — no manual intervention required. For Denver-area homeowners who travel, have medical equipment that requires power, or want whole-home protection without the hassle of manual operation, a standby unit is typically the better long-term investment.

Sizing Your Generator: Start With Your Loads

Generator sizing is measured in kilowatts (kW). The right size depends on which circuits and appliances you want to power during an outage. A common approach is to decide between two strategies:

  • Essential circuits only. A smaller generator (typically 10–16 kW) powers selected circuits — HVAC, refrigerator, lights, and a few outlets — while non-essential loads stay off. This is more affordable and sufficient for most outages.
  • Whole-home coverage. A larger generator (20 kW and up) powers every circuit in the house simultaneously, so life continues largely as normal. This makes sense for larger homes, homes with electric heating or cooking, or properties with multiple high-draw appliances.

At Denver’s altitude of around 5,280 feet, generators produce slightly less output than their sea-level ratings due to thinner air reducing engine efficiency — typically 3 to 5 percent less power per 1,000 feet of elevation above sea level. Your electrician or generator installer should account for this derating when sizing equipment for Front Range homes.

Fuel Source: Natural Gas vs. Propane

Most standby generators run on natural gas or propane. Natural gas is convenient if your home already has gas service — the generator connects directly to your utility line and you never have to think about refueling. Propane requires an on-site tank, but it works well for homes without natural gas service, rural properties, or locations where gas pressure might be a concern. Some generators are dual-fuel capable. Your installer can help you evaluate which fuel source makes sense based on your existing utilities and the size of generator you need.

Transfer Switches: Manual vs. Automatic

Any generator connected to your home’s electrical system — portable or standby — must be connected through a transfer switch. This is not optional; it is a safety requirement. A transfer switch prevents “backfeed,” where generator power flows back onto the utility lines and endangers utility workers and neighbors. Manual transfer switches require you to flip breakers to switch between utility and generator power. Automatic transfer switches (ATS) detect outages and switch over without any action on your part — standard on standby generators. The transfer switch installation is electrical panel work that requires a licensed electrician and permits in Colorado.

Permitting and Installation Requirements in Colorado

Standby generator installation requires electrical permits, and depending on your municipality, a gas permit as well. Inspections verify that the transfer switch is correctly wired, the generator is properly grounded, and the unit is sited with required clearances from windows, doors, and gas meters. Done handles the permitting and coordination as part of a generator installation so homeowners are not navigating that process alone. After installation, generators should be exercised regularly — most standby units run a weekly self-test automatically — and serviced annually to ensure they are ready when needed.

If you are ready to explore backup power options for your home, Done’s electricians can help you size the right system and handle the full installation. Visit our backup power page to learn more, or browse all of our electrical services. If you have questions about financing a generator purchase, our financing page has options that can help make it more manageable.