Generator Sizing

DETERMINING YOUR ENERGY NEEDS

BECAUSE WITH A GENERATOR, SIZE MATTERS
The first thing you need to do is determine what size generator would work best for your particular requirements.

This section will help walk you through that process.

When purchasing a generator, it's important that you select one that's capable of meeting your energy requirements.

  • You must match the rated output of the generator to the maximum anticipated power to be used.

This section will assist you in estimating the power requirements so you can purchase the generator that will satisfy your needs.

  • This includes using the accompanying worksheet to make a list of the tools and appliances you expect to operate, as well as the
    approximate power requirements for each device.

Once you have the list, you can estimate the highest demand that will be put on the generator under the "worst-case" conditions. With
this figure, you can determine the appropriate model generator for your particular needs.

WARNING: Electrocution, severe personal injury or death can occur: Do not connect any generator to any building's electrical
system unless an isolation switch has been installed by a licensed electrician. Refer to the Generator Owner's Manual.

CAUTION: Property damage can occur: Do not connect any generator to any building's electrical system unless an isolation
switch has been installed by a licensed electrician. Refer to the Generator Owner's Manual.

TAKE IT STEP-BY-STEP
Follow these steps when determining your energy needs:

1. Identify the wattage requirements for the tools and appliances that you want to power. The power requirement for the tool or
appliance can be found on its identification plate or in the Owner's Manual. If the power requirement is given in amps, multiply the amps
times volts to derive the required watts.

Amps x Volts = Watts

2. Add up the required watts of all the tools and appliances you expect to operate simultaneously.

3. The total watts derived in step 2 is the size generator you need. These three simple steps will "size" a generator.

The Additional Guidelines section explains the procedures to calculate and size for motor starting.

This chart lets you immediately add up all of the appliances you will most likely utilize:
GENERATOR WORKSHEET
 
RUNNING
WATTAGE
REQUIREMENTS
ADDITIONAL STARTING
WATTAGE
REQUIREMENTS
TOTALS
HEATING/COOLING
 
 
 
Furnace Fan, gas or fuel oil
furnace
 
 
 
1/8 horsepower
300
500
 
1/6 horsepower
500
750
 
¼ horsepower
600
1000
 
2/5 horsepower
700
1400
 
3/5 horsepower
875
2350
 
Central Air Conditioner
 
 
 
10,000 BTU
1500
2200
 
20,000 BTU
2500
3300
 
24,000 BTU
3800
4950
 
32,000 BTU
5000
6500
 
40,000 BTU
6000
6700
 
HEATING/COOLING
 
SUB-TOTAL:
 
KITCHEN
      
Refrigerator, Average
 600
 2200
  
Dish Washer - Cool Dry
 700
 1400
  
Dish Washer - Hot Dry
 1450
 1400
  
Clothes Dryer - Gas
 700
 1800
  
Clothes Dryer - Electric
 5750
 1800
  
Microwave Oven, 750W
 750
 800
  
Washing Machine
 750
 2300
  
Coffee Maker
 850
 0
  
Toaster - 2 Slice
 1100
 0
  
Toaster - 4 Slice
 1650
 0
  
Electric Skillet
 1500
 0
  
Electric Range 6-in element
 1500
 0
  
Electric Range 8-in element
 2100
 0
  
Freezer
 2500
 2200
  
KITCHEN
 
SUB-TOTAL:
 
BATHROOM
 
 
 
Hair Dryer
800-1700
0
 
Iron
1200
0
 
BATHROOM
 
SUB-TOTAL:
 
APPLIANCES
 
 
 
Lights-Wattage
Actual:
0
 
VCR
50
0
 
Heating Pad
65
0
 
Radio
100
0
 
Television - Black & White
100
0
 
Television - Color
300
0
 
Dehumidifier
400
0
 
Electric Blanket
400
0
 
Garage Door Opener - 1/4hp
550
1100
 
Garage Door Opener - 1/3hp
725
1400
 
Well Pump - 1/3 hp
750
1400
 
Well Pump - 1/2 hp
1000
2100
 
Sump Pump - 1/3 hp
800
1300
 
Sump Pump - 1/2 hp
1050
2150
 
Vacuum Cleaner - Standard
800
0
 
Vacuum Cleaner - Deluxe
1100
0
 
APPLIANCES
 
SUB-TOTAL:
 
COMMERCIAL PRODUCTS
 
 
 
1/4" Drill
300
300
 
Jigsaw
300
300
 
Electric Weed Trimmer
500
500
 
Router
1000
1000
 
Belt Sander
1000
1000
 
Disc Sander
1200
1200
 
Chain Saw
1200
1200
 
Worm Drive Saw
1560
3100
 
12" Concrete Saw
1800
3600
 
7 1/4" Circular Saw
1500
3000
 
Disc Grinder
2000
4000
 
Air Compressor, Average
2000
4000
 
COMMERCIAL PRODUCTS
 
SUB-TOTAL:
 
   
GRAND TOTAL:
  
ADDITIONAL GUIDELINES

CONVERTING AMPS OR HORSEPOWER INTO WATTS
If necessary, use these formulas:

Watts = Amps x Volts

Running Watts* = Horsepower x 932** (for motors)

Remember, this worksheet lists average power requirements — a particular manufacturer's device may use more or less than the listed
wattage.

  • Add a 10% correction factor to your totals to help overcome this uncertainty.

If your customer plans to operate devices that use electric motors, list both the starting and running requirements of each.

  • Starting requirements of some devices maybe significantly higher than their running requirements. This higher demand must be
    considered when estimating your power needs. Some small, universal motors — which do not draw a heavy starting load (drills, small
    saws, blenders, etc.) — require very little extra current for starting.

When listing items that use motors, take them in the order of highest-to-lowest starting requirements, as shown in the example below.
Motor A, for instance, has a starting requirement of 2,600 watts, so it's listed first, followed by Motor B at 1,300 watts, and Motor C at
1,000 watts.
MOTOR/DEVICE
STARTING WATTS
RUNNING WATTS
Motor A
 2,600
 850
Motor B
 1,300
 600
Motor C
 1,000
 750
Once you have compiled an accurate list of what you will be operating, you can calculate the maximum power requirements. There are
three different calculations you can make, depending upon the kinds of tools and appliances on the list, and their intended use:

  • No electric motors.
  • One motor running at a time.
  • More than one motor running at a time.

NO ELECTRIC MOTORS
If your list does not include any devices that use electric motors, simply add the power (running) requirements of all the items on your list to
obtain the maximum power needed.

  • For example, if you intend to use only an electric skillet, a 100-watt light and a heating pad (as shown below), the maximum power
    requirement would be 1,655 watts. In this case, a generator like the EF2800i, that can produce 2,500 watts rated output, is
    recommended.
DEVICE
WATTS
Electric Skillet
 1,500
Light
 100
Heating Pad
 65
Total:
 1,665
NOTE: The EF1600's rated output is 1,400 watts, so its output would be too low to handle this load on a continuous basis.

Footnotes:
*Running Watts is the amount of power a motor consumes once it has started to run at normal speed.
**932 is the factor used to convert motor horsepower ratings to needed electrical energy. It takes into account normal losses in utilizing
that power.