Running watts are the indication of power required to keep an appliance running whereas starting watts refers to the highest number of wattages required to start the appliance. These measurements are crucial for selecting the perfect backup generator for you.
A generator should be able to support both your total running wattage and the highest starting wattage. Let’s dig deeper and see how they differentiate.
What Are Watts?
Watts can be described as the unit to measure electrical power. It is measured by multiplying the voltage and the current of any electrical device. For those who aren’t familiar with the concept of power, it is the amount of work your machine can perform.
Almost all electric devices/machines come with a power rating or wattage that showcases how much power they need to consume in order to function properly.
Running watts
Not every machine will require the same energy to work, but they still need a basic amount of energy flowing through them to keep them running. The energy your machine will require just to stay running over a set amount of time will be noted as the running watts of your machine.
In the case of a generator, this will express the amount of wattage your generator will be able to provide while it’s running. Most generators are equipped with circuit breakers that’ll trigger once the load is equal to or greater than the running watts your machine can handle.
Starting watts
Most large and heavyduty electrical equipment needs a sudden surge of power to start working. This power can be 25 times bigger than its normal running watts. This sudden spike in energy requirement is known as the starting watts, surge watts, or peak watts.
The energy isn’t required continuously though. The machine will require the starting watts just for a couple of moments. Once the engine starts running at full capacity, the energy requirement will fall down to its original running watts.
Running watts vs starting watts: How do they differ?
The primary difference between the running watts vs starting watts is the amount of energy needed and the time the energy is needed for. A generator can typically supply both these wattages and help your appliances run smoothly.
Appliances need around 25 times more energy than their usual state when they start working. The surge power AKA the starting watts is used to generate that initial momentum that will start the device.
Once the sudden surge of power is over, the demand for energy drops and the running watts kick in. The device will continue to work at this minimum power level until it needs to start again. Your generator can easily supply this load over a long time.
Let’s hit the basics!
It’s time to dig a bit deeper. I’m confident that you probably learned about power, work, and energy in your high school physics class. For those who aren’t familiar, It takes more effort to move a heavier object and to move the same object further away, right?
The amount of effort won’t vary whether you are a man or a machine. The more you push a heavy object, or the same object to a location further away, the more effort it’ll take from you. This concept can be summarized in the equation below.
W = F * d
Where W = Work done (Joules), F = Force (Newtons), and d = Distance (meters)
However, we need another thing to calculate the power, and that is time. If the time is shorter, you’ll need to put more effort into moving the object and the opposite happens when you have a lot of time.
The measurement of work done over time is expressed through the term “Power” and is measured in watts. The more power you have, the more work can be done in a set amount of time.
So, the previous formula can also be expressed like this:
P = W / t
Where P = Power (Watts), W = Work done (Joules), t = Time taken to do the work (seconds)
Now, in comparison to the power generated from human strength, the electric power is a bit different. You’ll get the wattage (power) by multiplying the current (amps) and voltage (volts) passing through the machine. As a result, the abovementioned formula becomes like this:
P = I * V
Where P = Electrical Power (Watts), I = Current (Amps), V = Voltage (Volts)
This is the most basic form of electrical power. In reallife applications, there are a lot more factors that will determine the wattage of your machine.
How to Size Your Load?
In order to properly size your load, you need to figure out and list all the appliances that you want to run on your generator. This will determine what size generator you’ll be needing.
Here is the chart of some common household items that can give you a rough idea:
Appliance  Approximate Starting Watts  Approximate Running Watts 
Washing Machine  1600  800 
Electric Clothes Dryer  6750  5400 
Refrigerator  2200  700 
Microwave Oven (1000 watts)  1500  1500 
Television (16” Flat Screen)  190  190 
Dishwasher (Cool Dry)  540  216 
Electric cooktop  1200  1200 
Garage Door Opener  1420  720 
Sump Pump (1/2 Horsepower)  2150  1050 
RV Air Conditioner (15000 BTU)  3300  2000 
Blender  850  400 
Hair Dryer (1600 watts)  1900  1800 
Fan (portable)  120  40 
Hand Drill (1/2 in.)  900  600 
Automatic Washer  1200  1200 
Once you make a list of all the appliances you need to run, add all the running watts to get the total running wattage. This is the lowest amount of wattage you’ll need from your generator continuously.
For the starting wattage, find the largest starting wattage in the list. This represents the highest amount of watts you’ll need from your generator. If you want to figure out the total wattage required during a surge.
The formula looks like this:
Total wattage requirement = Total running watts + Maximum starting watts.
Using this formula, finding out the total wattage requirement for your generator will become much easier.
How To Choose the Correct Wattage
The only way to select the correct wattage for your backup generator is to go through the specifications the manufacturer provides. The specifications will include running watts and peak watts.
You need to make sure that your total running watts is within the generator running watt rating and the estimated surge watts stay comfortably within its peak wattage. Additionally, some outlets of the generator may have specific limitations on how much current it can handle.
That’s why going through all the specs is really important when buying a generator. A general rule of thumb is to multiply your estimated surge wattage by 1.25 and select a generator that has a higher peak rating than the number you came up with.
This will make sure that your loads won’t surpass 80% of the generator’s capability.
What Happens When the Generator Overloads?
In times of overloading, the load draws more current than the circuit can supply safely. However, the voltage is usually determined by the power source, the load (with high wattage) will try to get more power by drawing more current.
The generator will resist the process by creating heat. The heat will increase with time until the machine burns out or worse, catches fire.
Some generators, however, can drop the voltage in time of overload. That isn’t good either. Alongside generating heat, this can cause permanent damage not only to the generator but also to the appliances connected with it.
In the worstcase scenario, you’ll end up with some broken appliances in the middle of a fire hazard.
FAQs

How to calculate the wattage of an appliance?
Ans: For the running wattage, you’ll need to multiply the amperage with the voltage. If any appliance needs 10A (Ampere) and 110V (Volts) to run, the running wattage will be = 10 * 110 = 1100W.
You can find the starting wattage by a Wattmeter. Usually, they are 25 times the running wattage.

How many starting Watts does a refrigerator use?
Ans: That depends mostly on the size of the refrigerator, the year of production, the model, and the brand. Usually, most modern refrigerators require a starting wattage somewhere between 5002000W.

How many running watts do I need for a portable generator?
Ans: The total running wattage should be greater than the combination of the highest starting power needed by your appliances and the total sum of all the running wattage from all the appliances you want to power with the generator.
The formula is:
Total wattage requirement = Total running watts + Maximum starting watts.

How many watts does the average house use?
Ans: An average US home uses 900 kWh per month, which becomes 30 kWh per day or 1.25 kWh per hour. That means an average home in the US will require 1250W of wattage each hour.
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