Electricity from the utility company is great, that is until something interrupts it and it goes out. Power outages can be troubling and even life threating, so don't get caught without a backup generator system of some type to keep the power flowing. Backup generators come in many different styles. There are generators that connect to PTO drives on tractors, portable generators that run on gas, diesel, or propane, and others that connect more permanently to serve as a whole -house backup that run on propane or natural gas.
Along with these different types, one has to also consider the needed size to properly power your power needs. You must consider whether you are trying to just power the bare essentials during a power loss, or you'd like to have full power while the troubled power lines are repaired. Power consumption needs to be calculated and then used as a basis for the needed wattage of generator for your home. By adding up the wattage required to power lights, outlets, and appliances, you'll get a better feel for the actual power required. However, don't forget to calculate startup power, that is the additional power required to start such things as motors and the like. The initial power is more than the running power, so be sure to include that in your calculations. The surge wattage is best described by the power needed to get a motor turning, maybe twice the amount of the actual run wattage. The run wattage is the power needed to sustain the motor rotation, thus it requires much less than the surge wattage needed to make the motor start to spin from a stopped state.
The posted wattage that a manufacturer lists on their generators is called the run wattage. Therefore, if you have a 6,500-watt generator, your calculated run wattage is 5,000watts, but the startup surge wattage is 15,000 watts, you have already undersized the generator for a full power startup. Most generators have a startup wattage guide, but if you cannot find it, contact the manufacturer to learn the value before buying. Generally as a rule of thumb, the startup wattage is around double the amount of the run wattage, 13,000 watts in this case.
You may already own a generator that you have now discovered is underpowered for your home, now what? Don't fret! Although there are some generator that are incapable of generating much more surge wattage as the run wattage, all is not lost. With the startup of appliances over a period of time rather than all at once, you should certainly have enough power to run the home's power needs with this generator. Simply turn off all the circuit breakers, start the generator, and then slowly turn one appliance on at a time. That way, each will switch from surge to run power and the run power is well within the limits. * As a note, I'd rather not have the generator loaded to 100%, rather calculate the power load to 85% or less. If you work your generator to full capacity all the time, its lifespan will be much less. After all, a gas motor running at half speed will generally be a much quieter running machine and will run much cooler. The gas consumption will also come into play. Not only will it likely run longer, but it will save you money on the purchase of fuel during the downtime.
Although the surge wattage may add up to 13,000 watts, it is not necessary to purchase this large of generator if you're willing to stagger the startup of major appliances like air conditioners, water heaters, refrigerators, freezers, etc... If you don't want the worry about all this work, then you'll be better off to purchase a larger unit, if you pocketbook can handle the added cost. Let's take a look at a backup generator buying guide.
For a home up to 2,700 sq. ft. you'll need a 5-11 kilowatt generator. For a home up to 2,700-3,700 sq. ft. you'll need a 14-16 kilowatt generator. For a home up to 3,700-4,700 sq. ft. you'll need a 20 kilowatt generator.