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Standby Generator Buying Guide

If you're looking for a long-term backup solution that gives you dependable power whenever you need it, a standby generator is a good choice. Consider your power needs to determine the standby generator size that will work best for you.

Standby Generator

Standby Generator Basics

Standby generators are intended for permanent power protection. They produce consistent and stable power that computers and other sensitive electronic equipment can use safely. Standby generators can run for extended periods using a permanent natural gas or LP fuel supply. In a power outage, a permanently installed standby generator returns your home or business to power within seconds, even when you're away.

There are no extension cords to run no need to refuel with gasoline. A fully automatic standby generator senses an outage and begins producing power immediately. When power returns, the generator shuts itself off automatically and returns to standby mode. Because the generator is hard-wired into the electrical system of your home or business, appliances and devices such as furnaces, well pumps and lights will operate in addition to plug-in items.


Always follow the generator manufacturer's operating, maintenance and safety instructions.

How a Standby Generator Works

standby generator operation

An automatic standby generator works by constantly monitoring utility voltage. When there is an interruption in your electricity, the generator detects the problem and goes to work. Here's how:

  1. The controller in the generator monitors incoming voltage through the automatic transfer switch (ATS) — see below for more information on the ATS.
  2. When there is a power interruption, the controller waits 10 – 20 seconds, and then signals the generator to start. Within seconds, the ATS transfers to generator voltage.
  3. The ATS does this by safely closing the utility line and simultaneously opening the power line from the generator. This will stop any “back feed” of power to the utility lines of neighboring houses.
  4. Within 10 - 20 seconds, the standby system begins supplying electricity to the circuits you have chosen for generator power. The controller continues to monitor the utility line and is ready to transfer back to utility power when it returns.
  5. When the controller senses that utility line voltage has returned at a steady rate, it automatically transfers the electrical load back and resumes monitoring for another outage. The generator will continue to run for another minute to allow the engine to cool down.

Standby Generator Transfer Switches

If you have chosen an automatic standby generator, you'll also need a separate device called an automatic transfer switch (ATS) to connect the generator to your existing electrical system. Most automatic standby generators are pre-packaged with a transfer switch.

Although the generator creates the power, the transfer switch is really the core of your generator system. It is a permanently installed electrical panel near your main circuit breaker panel that allows you to safely connect a generator to your home's electrical circuits. As described above, the ATS constantly monitors incoming utility power and determines when a true power outage is occurring, switching from utility power to emergency generator power and back again when utility power returns. Options include transfer switches that provide power to only essential circuits or those that supply every circuit for whole-house coverage. Some allow for prioritization of optional circuits, or “load shedding,” where essential circuits remain powered and non-essential circuits cycle off if the generator approaches overload.


Watch our DIY Basics video: What's In My Breaker Box?

Good to Know

Do not attempt to install a transfer switch yourself. Installation of a transfer switch may require local permits, but always requires a professional electrician. The transfer switch model will depend mainly on the size of your generator.

Finding the Right Size Standby Generator

Often, generators come with a transfer switch containing a predetermined number of circuits based on the generator's kilowatt (kW) power rating. Each circuit connects directly to a matched circuit on the home's main circuit breaker panel, providing electricity to that specific appliance or area of the home. For example, with an 8kW generator and 10-circuit transfer switch, you can connect:

  • Lights and a TV in the family room
  • Lights and a microwave in the kitchen
  • A refrigerator
  • Power to a bathroom
  • A computer and home office equipment
  • A garage door opener
  • An air conditioner
  • A furnace


Here are some types of coverage to consider:

Essential Circuit Coverage: Many homeowners choose to cover only selected circuits during an outage, rather than all circuits. Essential circuits might include heating and cooling systems, refrigeration, lights or a well pump. This option is an economical solution that covers the basics during an emergency.

Managed Whole-House Coverage:  If you won't turn on every appliance at the same time (most people don't), a smaller generator, such as an 11kW or 13kW model and a 200 amp power management switch provides whole-house coverage by managing the power requirements of individual appliances.

Complete Whole-House Coverage: When the power goes out, everything comes on and stays on — no matter how many circuits you need to back up. Choose a backup power solution capable of covering every circuit in any size home for complete whole-house protection.


The most accurate way to select the right option is to have a Lowe's installation specialist conduct a load measurement of the circuits and items you intend to back up with your standby generator. An amp meter measures the power required as each appliance starts up. The result of this load measurement gives you the total power requirement for backup power.

Air-Cooled and Liquid-Cooled Generators

An air-cooled generator uses a fan to force air across the engine for cooling. For most homes, air-cooled models provide exceptional value. Depending on the model, one of these generators can power 8, 10, 12 or 16 key circuits in a main distribution panel during a power outage. A 20kW air-cooled standby provides whole-house protection for many homes.

A liquid-cooled generator uses an enclosed radiator system, similar to that in an automobile, for cooling. Larger kW generators require larger engines for higher power output. Generally, these generators are liquid-cooled.

Standby Generators Frequently Asked Questions

Why size a generator by circuits and not watts?

You can simplify the job of sizing a standby generator by matching the circuits between your home's main electrical panel and the generator system's load center. On the other hand, figuring out the specific wattage requirements of appliances and other items in your home can be difficult since they are plugged into outlets all over the house. By identifying the circuits to back up, you can easily decide how large a generator you need and what model will best fit that need. A licensed electrician should determine the electrical load and identify the circuits to back up.

What's the advantage of an aluminum or composite generator enclosure?

Aluminum and composite enclosures are naturally rust- and corrosion-resistant. For salt air or high humidity conditions, manufacturers highly recommend aluminum or composite to ensure decades of worry-free service.

Can an automatic standby generator replace utility service?

No. The generator fuel costs would be much more expensive than buying power from the utility company.

Can I install the generator myself?

As an option, manufacturers offer pre-packaged and pre-wired systems with comprehensive installation instructions. You could perform the simpler site preparation steps and have a professional make the electrical panel and fuel connections, or you could complete the entire installation yourself. However, for safety reasons and to ensure adherence to all local, state and national electrical codes, particularly for non-pre-wired or larger systems, manufacturers recommend you use an authorized dealer or licensed contractor.

Does the generator have to be maintained?

Yes. Simple maintenance is required. All generators require periodic oil and filter changes to ensure maximum performance for years of reliable service. Preventative maintenance kits are available. Refer to the owner's manual for routine maintenance procedures and schedules.

Can I purchase a service / maintenance contract?

Yes.  Your local installer may offer service / maintenance contracts for a worry-free ownership experience. Ask about availability and cost, which will be based on the service level you require. Cost will also vary based on hourly labor rates in your local area.

I don't have natural gas at my house. How long will a generator run on my propane tank?

Run time will vary with the size of the generator and the appliance load being placed on it. The chart below shows hours of operation for a typical 16kW generator running at half load.


  16kW Generator at Half Load

  LP Tank Size (gallons)





  Hours of Generator