Standby Generator Rankings - How We Rate Standby Generators

In this article, we will rank standby generators according to the intended use of the generator together with a home’s square footage. Also, we will list the pros and cons for each of the following three generator types: air-cooled, liquid-cooled NG/LP, and liquid-cooled diesel generators.

Air-Cooled Generators

We rate air-cooled generators a good, solid 3-Star rank out of 5-Stars. Air-cooled generators are friendly on the budget and offer true whole house generator coverage for homes up to 2,000 square feet. Because of built-in load management capabilities, a 20kW air-cooled generator also provides homeowners with Managed Whole House coverage for homes up to 3,000 square feet.

Managed Whole House generators manage the loads of up to four high electrical load appliances like air conditioners, ovens, clothes dryers, and electric hot water heaters. For example, the generator will manage the operation of two 5-ton air conditioners. While both A/Cs will not operate at the same time, the generator will automatically manage the operation of the A/C units.

Air-cooled generators are significantly less costly than liquid-cooled standby generators. Load management capabilities allow homeowners to maintain comfort levels while keeping project costs down.

All air-cooled generators regardless of manufacturer have an engine run speed of 3600 RPM while liquid-cooled generators can be ordered with an engine run speed of 1800 RPM. High engine run speeds consume engine oil faster than low-speed generators. As a result, we recommend shutting the generator down after 3 days of continuous operation to check engine oil levels. Use care not to overfill when adding oil.

We have compiled a list of the PROS & CONS of air-cooled generators below:

Read this article to learn how the Cummins RS20A 20kW air-cooled generator stacks up against its major competitor.


Liquid-cooled generators are sized to accommodate all house electrical loads. As a result, these generators do not have built-in load management. So, for example, if all house loads require a 30kW generator, homeowners should purchase a 30kW generator. The exception to this is when a home expansion is planned at some future point. Simply calculate the electrical loads with the expansion and purchase a generator that accommodates all existing and future loads.

Liquid-cooled generators have a radiator and water pump just like your car or truck.

The benefits of liquid-cooled generators operating at 1800 RPM include:

  • Quieter performance
  • Lower fuel consumption
  • Less engine wear and tear
  • The ability to sustain long duration power outages lasting a week or longer

Here’s our list of PROS & CONS for liquid-cooled generators operating at 1800 RPM:


Cummins diesel generators are designed to operate under extreme environmental conditions and are certified under the latest EPA, UL, and NFPA 110 standards.

The lifespan of a diesel generator is measured in decades. Many 30- and 40-year-old diesel generators are still in operation. The key to the longevity of any generator is routine professional maintenance and service.

A diesel fuel tank is mounted subbase and standard fuel tanks will operate the generator for at least 24-hours without refueling. Larger tanks are also available.

Homeowners concerned about possible earthquakes will benefit from a diesel generator. If a severe earthquake strikes the area, natural gas lines will break, and the local fire marshal will likely shut down natural gas lines. Repairs may take upwards of a year or longer.

Diesel generator PROS & CONS are listed below:


Two takeaways to consider include:

  1. Generator sizing is critically important and best performed by a generator industry professional
  2. Not all generators are created equal. Explore the options available which best fit your needs and budget.

Cummins generators are the most trusted name in standby power. A world leader in power generation products, Cummins Power Generation offers a variety of standby power generation products for the best in reliability, durability, and power.