What Size Generator Do I Need?

The whole point of buying a generator is so that you won’t have to sit in the dark during blackouts. This may be compromised if you do not know what size of a generator will work best according to your needs. 

There are a number of things that you should consider when buying a generator. Knowing what size of a generator you need is very important. 

To determine the size of the generator, you need to know the starting wattage of the appliances that you intend to power. Then, go for a generator that has a power output that exceeds the total wattage of all the appliances that you intend to use.

What Is The Size Of A Generator?

The size of a generator implies how much power it would be able to generate. When it comes to generators, the basis for determining the size is the electrical output and not the physical dimensions of the generator. 

The electrical output should exceed the power input required by all the appliances that are to be run. To determine the required input, you need to find out the starting and running wattage of the appliances. This information can be found in the owner’s manual or on the identification plates of the equipment.

If the generator is too small, it would not be able to bear the load of all the appliances. This may damage the equipment as well as the generator. And too large a generator would only increase the cost of operating it.

So, as I said, it is very important to know how to determine the size of a generator that would be best suited to your needs.

What does running watts mean?

Running watts mean the maximum power output a generator would provide without running the risk of getting damaged.

For electrical appliances, running wattage means the minimum amount of power an appliance consistently needs to work.

For example, a light bulb has a running wattage of 1 watt. This means that you will need an output of at least 1 watt from your generator to light a bulb.

What does starting watts mean?

Starting wattage is the maximum number of watts that a generator can produce for a short amount of time. When appliances that require a large power input to start are in use, you need to check whether your generator would be able to sustain that surge in power for that short period. 

How To Calculate What Size Generator I Need?

So, the most important factor in this calculation is the power output of the generator. It is usually measured in watts. 

The generator should be able to produce enough power to run the most-needed household appliances. Usually, a generator that can deliver 10,000 Watts is best for the purpose of running the electrical equipment in a house.

The second step is finding out how much power is required as per your energy needs. 

Step 1 – devise a list of equipment you need to run

If you need a generator for your house, put all the appliances that you would need on the list in case of an emergency. 

This includes the air conditioner, fridge, TV, circuits for lights, etc. But, it depends on what appliance is necessary for you.

Step 2 – Calculate the power requirements of your list of equipment

As I have said earlier, there are two things to consider when calculating the power requirement of your electrical equipment; the starting watts and the running watts.

Starting watts are the number of watts an appliance needs to start. Some appliances, such as an air conditioner, need high power to start. This would put an added strain on the generator for a short while until the equipment starts. 

Running watts is the amount of power an appliance needs to run in its usual course. 

For example, a 10,000-watt air conditioner would need 2,200 watts to start. These are the starting watts. After starting, its power demand decreases. Then it needs 1,500 watts continuously to work. This is the running wattage.

Both the starting and running watts of a generator should meet the requirement of any appliance that you wish to run on it. So, a 2,000 Watt generator would be enough if you would want to run only a 10,000 Watt A/C.

Step 3 – choose a generator that is a little better than your requirement

It would be wise to choose a generator that has a slightly greater output than you require. This is beneficial in a number of ways.

One, it is better to be safe than sorry. A few extra hundred watts would eliminate any risk of your generator shutting down due to overload.

Secondly, if you run a generator at full capacity, it would considerably decrease its useful life. Being consistently run on full load puts a strain on the working efficiency of the generator.

Also, a generator produces far more noise when it is being run at full capacity. It could become an annoyance for you and your neighbors.

Generator Calculator

Use the calculator below to find out what your required wattage is. Simply, select the name of the appliances you wish to use and the calculator will determine the size of the generator that would be best for you.

What size generator do I need for my house?

The following chart will help you answer the above question.

Heating/CoolingRunning wattsStarting watts
Air Conditioner – window 15002200
Air Conditioner – window 13000 BTU18002800
Air Conditioner – window 10000 BTU15003000
Air Conditioner – window 24000 BTU38005000
Air Conditioner – window 40000 BTU60006700
Heating/CoolingRunning wattsStarting Watts
Furnace Fan – Gas or Fuel Oil – ¼ HP6001000
Furnace Fan – Gas or Fuel Oil – ½ HP8752350

What size generator do I need for my RV?

The generator should have a wattage that is greater than the cumulative wattage of all the appliances. Both the starting and running energy should be taken into account for this purpose.

The following chart gives the starting and running watts of a set of appliances used in an RV.

Heating/CoolingRunning wattsStarting watts
Air Conditioner – window 15002200
Air Conditioner – window 13000 BTU18002800
Air Conditioner – window 10000 BTU15003000
Air Conditioner – window 24000 BTU38005000
Air Conditioner – window 40000 BTU60006700
Heating/CoolingRunning wattsStarting Watts
Furnace Fan – Gas or Fuel Oil – ¼ HP6001000
Furnace Fan – Gas or Fuel Oil – ½ HP8752350

And a regular tailgating party will require a 2000-Watt generator.

FAQ

What size generator to run a refrigerator and freezer?

A typical refrigerator/freezer would need a starting wattage of 1600 and a running wattage of 800. Be careful that your appliance would not start and may even get damaged if it does not get enough power to start. 

The generator’s capacity should be greater for both starting and running the appliance

What size generator to run an air conditioner?

The size of a generator to run an air conditioner depends on the size of the air conditioner. A typical window air conditioner needs a starting wattage of 2,200 and a running wattage of 1,500.

The wattage of other types of air conditioners is given in the table below:

Heating/CoolingRunning wattsStarting watts
Air Conditioner – window 15002200
Air Conditioner – window 13000 BTU18002800
Air Conditioner – window 10000 BTU15003000
Air Conditioner – window 24000 BTU38005000
Air Conditioner – window 40000 BTU60006700

What size generator to run a furnace?

The power starting and running power required by furnaces is given below

Heating/CoolingRunning wattsStarting Watts
Furnace Fan – Gas or Fuel Oil – ¼ HP6001000
Furnace Fan – Gas or Fuel Oil – ½ HP8752350

Wrapping it up

Now you know what to consider before buying a generator. You are aware of the power requirements of your house or RV. You know how to calculate the total starting and running watts of appliances and buy a generator accordingly. 

This is everything you should have knowledge of and will help you make the best decision. 

Happy buying!

Leave a Comment