Pasadena Water & Power

Guide to Generators

Generator Header 

Finding the Right Generator Capacity

Finding your household’s wattage needs is the first step to choosing a generator. Avoid purchasing the wrong size of generator by calculating the correct amount of power you may need.

Choose what appliances are important to you during an emergency and write down the wattage found on the appliance label. An appliance’s “Starting Power” refers to the wattage the appliance needs in order to start up, and the “Rated Power” is the amount of power needed to stabilize and remain operating.

Identify the total wattage required to power those products. For example, if a refrigerator, space heater, and laptop computer are essential appliances, the ideal generator size would be 4,000 watts or greater.

Use this chart of common appliances to help calculate your capacity needs:   

Major Appliance  

Additional Starting Power (watts)  

Estimated Rated Power (watts)  




Electric Water Heater 


Space Heater 


Window AC (12,000 BTU) 



Central AC (40,000 BTU) 



Lightbulb (75 watt) 


Electric Stove 


Garage Door Opener 



PC Computer 


Laptop Computer 


Choosing Between a Stationary or Portable Generator 

Once you have determined the size of your generator, the next step is to choose between a portable or stationary generator. Portable generators usually provide up to 10,000 watts of power while stationary generators can provide up to 20,000 watts. The following tips will help you consider the added benefits and challenges of each option.

Stationary generators start up automatically when power goes out.

Stationary generators can be significantly more expensive and will require an electrician to install both the generator and the additional transfer switch necessary for automatic start-up.

Stationary generators that run on natural gas can connect directly to your home’s natural gas supply, which means you never have to worry about running out of fuel.

Portable generators are conveniently mobile, giving you the flexibility to use it in places other than your home.

Portable generators that run on gasoline require a large quantity. The fuel is highly flammable and will need to be stored safely.

Portable generators have to be physically turned on in order to operate. If you depend on an appliance that cannot be turned off, consider a stationary generator with an automatic start.

Portable generators are much more affordable, but can require a lot of labor to move, refuel, and maintain. 

Portable Generator Guide

If a portable generator fits your household needs, determine the best one with the following tips:  

Additional Features

Additional features will enhance your generator’s capabilities, but will also increase the final cost. Narrow down what generator is best for your needs with a few of the available options for portable generators:

Inverter Feature: Traditional portable generators do not produce a stable enough frequency to run sensitive appliances such as laptops, televisions, and cell phone chargers. Inverter generators produce “clean”, safe power and are also much quieter than traditional portable generators.

Easy Startup: Instead of the often cumbersome pull-start mechanism, some portable generators offer a convenient electric start up feature that powers the generator at the push of a button.

Wheels: Portable generators can weigh up to 300 pounds, so look for ones already equipped with wheels. This feature is available on most portable generators with capacities over 2,500 watts.

Fuel Type: Most portable generators can run on gasoline or propane. Gasoline is more common and easily available, but can also be expensive and toxic. Propane is cleaner burning and has a much longer shelf life than gasoline, but it is not as energy efficient. Portable generators with dual fuel tanks are also available for optimum convenience during an emergency.

Generator Checklist

Add these necessary items in order to properly operate your new generator:   

Heavy-duty extension cord: Get the safest extension cord possible for your generator by matching the amps on the generator with the amps on the cord. Use the formula: Watts = Volts x Amps. For example, a 5,000 watt generator powering appliances that run on 120 volts will need a cable rated for at least 25 amps.  Also, make sure to purchase the thickest gauge possible once you know how many amps your cord will need. 

Transfer Switch: This optional device connects the generator to your circuit panel, allowing you to turn on all connected appliances in one place.

Fuel container: Consider purchasing at least two five-gallon fuel containers to ensure you have sufficient fuel on hand.

Fuel Preservative: Many fuel preservatives and stabilizers are available to keep your fuel fresh for up to two years. Make sure to find the proper preservative for your choice of fuel.

Generator Cover or Tent: If you cannot operate your generator in a weather-proof space (at least 20 feet from your home), purchase a cover or tent to protect it from weather elements. 

Important Tips When Using a Generator

Maximize the life of your generator by performing the following best practices:  

Plug each appliance into the generator one at a time to avoid exceeding the maximum power threshold and tripping the generator’s circuit breaker.

Make sure to use a portable generator at least 20 feet from your home and in a well-ventilated area to prevent carbon monoxide death.

Once a month, let your generator run for 20 minutes to lubricate the engine and recharge the battery.

Test run your generator at least every three months and plug devices directly into the generator to ensure it is running properly.

Remember to store fuel containers away from the generator and other sources of ignition. The maximum amount of gasoline legally allowed in Pasadena is 30 gallons. Any amount over 10 gallons should be stored in a flammable liquids cabinet.

Use stabilized fuel and change the fuel annually to ensure proper operation and avoid costly repairs (oil oxidizes over time). Prevent spills by using a wide, clean funnel to refuel.

Properly dispose of old fuel at a S.A.F.E. Collection Center (call 1-800-98-TOXIC for more information).

Check the air filter on your generator regularly and clean it according to the manufacturer’s specifications.



Visit the following online resources for more information about generators. Note that PWP does not endorse any particular brand or feature on these websites:  


Water Usage Gauge