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With Cummins Onan residential standby power systems, there are a variety of output sizes from 12 kW and higher. The best match will depend on the power (wattage) requirements of your home and the available fuel types. Some appliances with electric motors (refrigeration, air conditioners), require up to 2 to 3 times the listed wattage. The generator should be 20% larger than calculated requirements. Also, additional capacity allows more circuits to be added for future use.

How much power do you need?

Generators produce AC voltage, very similar to the voltage available in your home, however while your electric utility company produces sufficient power for all your electric powered devices, a home standby generator is limited in power output directly related to the engine horsepower. The amount of power that a generator can produce is rated in watts. Rated power is less than peak power as certain components lose efficiency as they are heated from use.

To determine wattage requirements you should determine which devices need to be powered simultaneously and what are the starting requirements. The wattage chart is provided below to assist you. Remember that with simple "power management" techniques, a small generator can provide adequate power for home or recreational applications.

The wattages listed below are based on estimated wattage requirements. For exact wattages, check the data plate or operator's manual of the item you wish to power.

Tool or Appliance	Running Watts (Rated)	Starting Watts (Peak)
Ceiling Fan	800	1200
Central AC - 10,000 BTU*	500	3000
Central AC - 24,000 BTU*	3800	4950
Circular Saw - 7 1/4"	1400	2300
Clock Radio	100	-
Clothes Dryer - Gas	700	1200
Coffee Maker	1500	-
Computer - 17" Monitor	800	-
Deep Freezer	700	1000
Dishwasher - Hot Dry	1500	1500
Electric Water Heater - 40 Gallon*	4000	-
Fax Machine	65	-
Furnace Fan	800	1300
Garage Door Opener	750	1200
Hair Dryer	1250	-
Hot Plate	2100	-
Inject Printer	80	-
Iron	1200	-
Laser Printer	950	-
Microwave Oven-1000 Watt	1000	-
Miter Saw - 10"	1650	2400
Oscillating Fan	200	400
Quartz Halogen Work Light	1000	-
Reciprocating Saw	1200	2000
Refrigerator/Freezer	700	1500
Security System*	500	-
Space heater	1800	-
Stereo Receiver	450	-
Sump Pump	800	1200
Table Fan - 14"	200	400
Television - 27"	500	-
Water Well Pump - 1/3 HP (220V)*	1000	2000
Window AC - 10,000 BTU	1200	2200

* These unit are usually hard-wired and require a professionally installed transfer switch.

Additional Power Considerations

Some appliances need a "surge" of energy when starting. This means that the amount of electrical power needed to start the appliance may exceed the amount needed to maintain its use. Electrical appliances and tools normally come with a label indicating voltage, cycles/Hz, amperage (amps) and electrical power needed to run the appliance or tool. Check with your nearest dealer or service center with questions regarding power surge of certain appliances or power tools.

Electrical loads such as incandescent lamps and hot plates require the same wattage to start as is needed to maintain use.

Loads such as fluorescent lamps require 2 to 2 times the indicated wattage during start-up. Loads for mercury lamps require 2 to 3 times the indicated wattage during start-up.

Electrical motors require a large starting current. Power requirements depend on the type of motor and its use. Once enough "surge" is attained to start the motor, the appliance will require only 50% to 30% of the wattage to continue running.

Most electrical tools require 2 to 3 times their wattage for running under load during use. (For example, a 9,000 watt generator can power a 3,200 to 7,000 watt electrical tool.)

Loads such as submersible pumps, air conditioners and air compressors require a very large force to start. They need 3 to 5 times the normal running wattage in order to start. (For example, a 5,000 watt generator would only be able to drive a 1,800 to 3,100 watt pump.)

If the power consumption of electrical appliances exceeds the operating range or if there is short circuit or other problems in the appliances, the AC breaker could trip "OFF" or the rotation of the generator could be abnormally reduced. In this case, stop the generator to see if the power consumption of the appliances is too large and if there is a problem in the appliances.

What type of fuel is best?

This depends on many factors - shelf life, cost, storage location, availability, etc.

LP (PROPANE):
Advantages

• Long shelf life
• Clean burning
• Easily stored in both large tanks or in smaller 5-10 gallon cylinders
• Obtainable during power outages - gas stations may be unable to pump other fuels during an area wide outage but, LP tanks are usually stocked full
• Home delivery available for larger tanks is commonplace

Disadvantages

• Pressurized cylinder of flammable gas
• Fuel system is more complicated (increased possibility of failure)
• Larger tanks are not aesthetically pleasing (unsightly)
• Fuel systems plumbing results in higher installation cost
• Some local ordinances prohibit the use of high pressure LP in residential applications

NATURAL GAS:
Advantages

• Usually unlimited fuel source - refueling not necessary
• Clean burning
• Almost always available during power outages
• No unsightly tank required

Disadvantages

• May be unavailable during natural disasters (earthquakes, etc.)
• Lower power output (30% less BTU's per unit than gasoline)
• Larger tanks are not aesthetically pleasing (unsightly)
• Fuel system plumbing results in higher installation cost
• Not available in many areas

DIESEL:
Advantages

• Least flammable fuel source
• Clean burning
• Easily obtained
• On site fuel delivery available
• High BTU output fuel

Disadvantages

• 18-24 month shelf life
• Installing large storage tanks raises cost of system
• May not be available during power outages
• Unpleasant smell

Help Determining Your Home Standby Requirements

A homeowner should not attempt to specify and install a power system on their own. In all cases, they should contract a Cummins Onan Dealer and/or certified technicians. Our sales and service locator will direct you to your nearest qualified Cummins Onan dealer or distributorship.