Standby Generator Buyer Guide: What Size ...

Author: Marina

May. 13, 2024

Standby Generator Buyer Guide: What Size Do You Need?

Written By: MJ Logan

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Standby generators do exactly what their name suggests—they stand by until the power goes out. Fully automatic, a standby generator engine starts within seconds after an outage hits, and it begins producing power. The Automatic Transfer Switch (ATS) isolates the house from the electric utility and connects the generator to restore power. The whole process takes less than a minute and as little as ten seconds.

The first step in the purchase process is determining the type of installation the homeowner needs and the size of the generator to buy. For residential homeowners and businesses, there are three general categories to consider:

  • Whole House Generator
  • Whole House Generator with Power Management
  • Generator for Essentials

Backup Generator Terms to Know

Whole House Generator System

The term "Whole House Generator" refers to an automatic transfer switch connection to the main panel. In this configuration, the transfer switch installs between the utility meter and the main circuit breaker panel with connections for both the generator and the utility lines. The switch isolates generator power from utility power, and the two never coexist on the same lines simultaneously. Normally, the switch selects utility power and feeds the house from the utility. During an outage, after the generator starts and is ready to accept the load, the transfer switch disconnects the utility and only then connects the generator. When the utility restores power, the switch disconnects the generator first and then reconnects the utility.

By feeding the main circuit breaker panel from the generator, a whole house generator powers everything, including major and large appliances like electric ranges, HVAC, and water heaters. It has the capacity to power everything at once—even multiple air conditioners running simultaneously. For a large home, this could mean a liquid-cooled generator with ample capacity. This is the most expensive category, but it offers exceptional reliability, especially in hot climates. Luxury homes, estates, and small businesses with larger power needs often use generators up to 150kW.

Power Management allows a smaller whole house generator to power anything in the house, but it might not power everything at once. For example, in a home with two air conditioners, the second unit might wait for the first to shut off before it starts. Large appliances like air conditioners are run according to priority. Your electric dryer might have a low priority, while the well pump has a high priority. Some of the newer power management systems allow priorities to change as needed with a convenient smartphone app. A whole house generator with power management uses a smaller generator that costs less to purchase and install and uses less fuel than the larger liquid-cooled models.

Essential Circuits Generator

Generators for essential circuits only power the most important circuits. Before installation, the homeowner chooses which circuits are most important. The transfer switch has a limited number of circuit breakers. During an outage, only the circuits chosen by the homeowner have power. An essential power generator will cost less than a whole house generator with power management for the same size house.

Common Circuits for Essentials

  • Air Conditioner
  • Furnace
  • Refrigerator
  • Freezer
  • Sump Pump
  • Garage Door
  • Well Pump
  • Kitchen Lighting and Appliance Outlets
  • Circuits with Medical Equipment

The air conditioner could be essential for someone especially sensitive to heat. In the winter, the furnace keeps the home comfortable. Refrigerators and freezers stay cold and preserve food. Sump pumps keep basements from flooding. Homes with a garage door opener should maintain access to their vehicle. It's essential to drink water, use plumbing fixtures, cook food, and have a few lights. Medical equipment is also essential.

Generator Size

Smaller homes have lower power needs than larger homes. A home in the Desert Southwest probably uses more power in the summer than one near the northern border. An important part of sizing includes local building codes which may include requirements not listed here. A whole house generator for a small home might only have enough capacity for essentials at a large home. A whole house generator with power management for a large home is probably more power than a small home needs.

It all depends on your home and family's power requirements. It's also important to choose a generator with a little more capacity than you need. Air-cooled generators, in general, should run at no more than 80 percent of their rated capacity most of the time. Short periods at close to maximum capacity won't hurt the generator. Just like a car, you don't drive at full speed for very long.

What Size Generator Do I Need for My House Calculator

What Size Standby Generator Do I Need? For more information, you can view details here. And if you are interested in a 45 kw diesel generator, contact us today for expert consultation.

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