How to Calculate Generator Wattage for a Home

Starting watts and running watts on a generator listing

A generator listing carries two watt figures. The first is usually the starting watts, also called peak or surge watts: the extra power a motor draws for the moment it starts. The second is the running watts, the steady draw while the motor keeps going. The U.S. Energy Information Administration explains that electricity is measured in units of power called watts. One watt is a very small amount of power, but some devices need only a few watts to operate, while others need many thousands.

Not every appliance has a starting surge. Items without motors draw about the same watts while they run. Items with motors, such as a refrigerator compressor, a well pump, an air conditioner, or a furnace blower, draw more at the instant they start. The difference between the two figures is the surge you need to cover when a motor kicks on.

These are listing words, not promises. The maker's page states the watt figures for a model; the listing may show one figure, two figures, or a watt group. Read the listing terms before you compare models.

Why the first figure on a listing is usually the starting watts

Sellers place the higher figure first because it shows what a generator can handle at the instant a motor starts. On this site, the buying guides group generators by the first watt figure in the title. That lets you quickly compare the surge capability of different models.

When a listing shows two watt figures, the larger one is usually the starting figure and the smaller one is the running figure. The listing may not state which is which, so check the maker's page for the model to confirm. If the listing shows only one figure, read that as the starting watts and locate the running watts on the maker's page.

Some listings use words like 'peak watts' or 'surge watts' for the starting figure. The running watts might be labeled 'rated watts' or 'continuous watts'. Knowing these synonyms helps you read a listing correctly.

A step-by-step method for a Texas home

You can match a generator to your essentials with a short list. This site does not publish appliance wattages, so the numbers for your own appliances come from the appliance nameplates, the maker, and a licensed electrician. The method below is a way to organize that information and compare it to a listing.

The method is a way to read the listing, not a promise that a given wattage powers a given appliance. The match between a generator and your home's load is a question for the maker and a licensed electrician. They can confirm whether the generator's starting and running watts cover the items you plan to run at the same time.

• List the essentials you would keep on during an outage: lights, a refrigerator, a well pump if you have one, a furnace blower in winter, a window air conditioner or fans in summer, a router, and phone chargers.
• Separate the items with motors. Those are the items with a starting surge.
• Add the running watts of every item you would run at the same time. That is the steady load.
• Add the largest starting surge in that list. That is the load the generator must cover at the moment a motor starts.
• Compare the total to both watt figures on the listing and the maker's page.

Decide between essentials and the whole house

Before you shop, decide whether you want to keep only the essentials on or power the whole house. That choice changes which listings you compare. 'Home Backup' and 'Whole House' are the seller's words; they describe intent, not a measured match. A portable generator with 'Home Backup' in the title may still need to be connected through an inlet and transfer switch, and that work belongs to a licensed electrician.

For essentials, compare your load total to the running watts and the starting watts on the listing; the mid-size guide lists portable units for that job. For the whole house, an installed standby unit is a different listing type; see standby versus portable for how the two differ, and the whole house guide for standby listings.

A whole-house standby generator is installed by an electrician and connects to a transfer switch. This site does not give wiring advice. The transfer switch is a term you will see on a standby listing; its size and installation are decided by an electrician and the local permit office.

What to check for Texas seasons and home types

Before winter storm season, your essentials list includes a furnace blower and lights. The CDC's winter weather guidance suggests preparing your home and supplies ahead of a storm. The Texas Division of Emergency Management and Texas Ready pages list what to prepare; this site does not predict when the grid goes down.

A rural home on a well adds a motor with a starting surge. Sizing that load is a question for the maker and an electrician; compare large portable listings if you want a portable unit.

A home on a propane tank changes the fuel, not the watt math. A dual fuel listing that runs on gasoline and propane gives you a second fuel choice. The EIA explains that propane is one of the hydrocarbon gas liquids, and natural gas is a fossil fuel. The choice of fuel is separate from the watt figures.

A close neighborhood changes the generator type, not the watt figures. Inverter listings are a separate listing type to compare, and an electric start listing narrows the list for winter mornings. These features do not change the starting or running watt math.

What this site cannot say about sizing

This site has no measured output, runtime, or fuel use data. It does not state that a given wattage runs a refrigerator, a well pump, an air conditioner, or a space heater, and it publishes no appliance wattage tables or worksheets.

The listing and the maker's page state the watt figures. Whether a generator matches your load is a question for the maker and a licensed electrician. Follow the maker's manual for use, care, and maintenance.

A generator listing does not include runtime or fuel use figures on this site. Those details, if available, appear on the maker's page. This site does not compare runtime because the catalogue does not state it.

What to pick for your situation

Questions

What does the first watt figure on a generator listing mean?

It is usually the starting watts, the surge a motor draws at the moment it starts. The running watts is the steady draw and is often the second figure. Check the maker's page to confirm which figure is which.

Do I add every appliance in the house?

No. You decide which items are essential and which you can do without. The summed load is then compared to the listing's watt figures. This site does not size a home; the maker and a licensed electrician do.

What is a starting surge?

A motor draws extra watts for a moment when it starts. That brief surge is the starting watts. Items like a refrigerator compressor, a well pump, and a furnace blower have a starting surge. The running watts cover the steady draw after the surge.

Why does this site not give runtime or appliance wattages?

The catalogue has no measured data for those figures. The listing and the maker's page state the watt figures; an electrician and the maker decide whether a generator matches your load.

Where do I find the running watts for a model?

On the maker's page for that model. The listing may show only the first figure, which is usually the starting watts. If two figures are present, the smaller one is usually the running watts.