How to size a residential generator

Are you looking for a residential generator that’s just right for your needs? With all the different sizes, models and features there is to choose from, it can be overwhelming to decide which one is right for you.

This guide will provide you with everything you need to know to find the perfect residential generator.


Generators are reliable sources of power that can provide a backup source of energy in any situation. While most generators are designed for commercial and industrial use, there are also residential generators available for home usage. A qualified contractor can help size the proper unit and determine your power needs so that you can choose the best generator for your home.

This guide will give you an overview of the process and criteria to consider when sizing a residential generator. The information provided here is general in nature and does not take into account all possible factors that may affect the sizing of a particular generator. It is important to consult with a qualified contractor to ensure that all factors are taken into consideration before deciding on the appropriate size generator for your needs. In addition, local codes and zoning requirements should be reviewed prior to installation.

Explanation of residential generators and their importance

Residential generators provide residents with a reliable source of backup power in the event of a power outage, either due to natural causes such as stormy weather or unexpected utility issues such as an overloaded circuit. Furthermore, they are also capable of powering other appliances or gadgets such as air conditioners, refrigerators, and hot water heaters. Knowing which size is appropriate for your particular home is important for power continuity in the event of outages.

It is important to take into account your home’s generator size requirements before making any purchase. Depending on the type of generator you choose—whether it is a portable or permanent installation unit—you must determine what size it should be based on the wattage necessary to run all connected circuits and appliances in your home. It is essential that you have enough wattage to support all major appliances and electronics; otherwise, your system will be unable to maintain continuous power supply throughout your entire home during outages.

Additionally, you must also consider other factors such as safety features, fuel types available, ease of use and maintenance requirements, noise levels emitted by generators when operating at full capacity or selecting between manual or automatic operation modes. All these fine details should be taken into account prior to purchasing a generator so that you can make an informed decision about which model best suits your needs and budget without sacrificing functionality or reliability.

Determining Power Needs

Determining the power needs of your home requires some planning and research. A qualified electrician or home energy auditor should be consulted if you are uncertain about the power needs for various appliances and electronics in your home.

To get started, draw up a list of all fixed appliances that you would like to have powered by your generator (i.e. refrigerator, stove, air conditioner, water heater etc.) in order of priority. Also consider any additional items that you may need to operate simultaneously such as extra lighting, fans and computers and account for future power upgrades such as adding a hot tub or an automated irrigation system to your yard.

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To estimate the total power requirements, add up the capacity (in Watts or Kilowatts) listed on each appliance label (generally found on the back). Carefully read appliance labels to avoid including less efficient items such as window air conditioners which usually require more power than similar-sized through-the-wall units. Power ratings for items like furnaces generally appear on their nameplates; larger systems may include separate ratings for blower fans and heating elements so be sure to check them both if applicable.

In addition, consider outside activities such as powering outdoor recreational equipment or home workshop tools during an outage because these can provide additional drains on energy supplies. Finally, remember to factor in some extra watts for future adjustments – after all it’s better to be safe than sorry!

Understanding power needs in the home

Knowing the power needs of your home is an important step before you select and purchase a residential generator. Your generator should be able to provide enough wattage to power your home without overloading, tripping breakers, or damaging items. It’s best to start by evaluating the wattage needs for various areas in your home.

The first step is to determine what items require power during an outage. These would include essential items such as refrigerators and freezers, sump pumps, lights, chargers for phones and similar electronic devices, heating and cooling systems, and anything else you would need in order to live comfortably during an outage. Important appliances such as stoves and water heaters probably won’t require backup power as they can typically use alternate sources of energy such as propane or natural gas. Once you’ve determined what will need a backup source of power it’s time to calculate the total wattage needed for all of these items.

You will then want to look up the wattage specs for those items that don’t have them listed on them (like lights). You should add up the startup watts for all devices that need power during an outage. This would include main components like motors in refrigerators or air conditioners which require more watts on start-up than with normal running use—be sure to convert this wattage from amps if necessary. Additionally any battery backups or inverters you plan on running should also be taken into account since they can draw quite a bit of extra wattage when first plugged in or turned on.

Once you have totaled the approximate starting wattages of all required appliances add a safety buffer of at least 20 percent more capacity than your calculated sum to allow for fluctuations such as lights being turned on or other unexpected loads being added on unexpectedly—or even unforeseen problems with one appliance that draw more than expected if something is malfunctioning inside it (such as additional starting loads from failing motors).

Finally avoid picking undersized portable generators that may not have enough capacity for powering multiple outlets at one time because those often fail quickly from overload conditions due to incorrect sizing—or be sure you are using multiple outlet cables with each outlet connection so you can spread out usage across multiple circuits thus avoiding breaker trips due oversizing issues when connecting too many items directly into single outlets at once within portable generators – this way distribution across many circuits is maintained even when portable generators are used outdoors!

Identifying essential and non-essential loads

A generator must be sized to meet the “essential” and “non-essential” power requirements (load) of a home. Essential loads consist of items that are essential for health, safety, or life comfort—such as lighting, heating/cooling systems and refrigeration—so they may need to be powered at all times during an outage. Non-essential loads are usually involved in entertainment or convenience.

When sizing a residential generator for essential and non-essential loads, there are several considerations. These include: wattage, the amount of power needed to run electronic equipment; availability of fuel sources; special applications such as Security or HVAC systems; local building codes; noise emission ratings; load shedding/priority load management features. Once all essential and non-essential load requirements have been identified, the next step is determining how much power can safely be provided by the generator. Installation of a generator must not overload it with too many circuits or draw too much current from any one circuit. This calculation needs to take into account both running (continuous) and starting (inrush) wattages for each device that will be connected to the generator’s output. An easy way to calculate this is using “rule-of-thumb” equations which factor in both running and start up wattages accordingly and ensure proper overload protection on all circuits being powered by the generator.

III. Types of Residential Generators

When shopping for a residential generator, you will come across two main types — standby generators and portable generators. Standby generators are permanently installed outside the home and connected to an inlet gas line. This type of generator is designed as an emergency power supply that automatically turns on when the main power source goes out. Standby generators are generally more powerful than portable models and are less likely to run out of fuel.

Portable residential generators provide emergency power for short-term use, such as during a power outage or when used in combination with a recreational vehicle (RV). Portable models are typically used to power appliances through the use of extension cords running from the generator to household appliances. They also require manual setup since these models must be moved close to an outlet for refueling purposes and turned on each time it is needed.

Explanation of different types of residential generators

When it comes to size, residential generators come in a variety of forms. From quiet models used to power essential household items during a blackout, to large, industrial-strength machines used to power larger homes and businesses, selecting the right generator can be difficult. The following is an overview of the different types and sizes of residential generators available:

Portable Generators: Portable generators are the most common type of residential generator due to their ease of installation and transportability. Portable generators range in size; most units generate between 1,000 and 12,500 watts or 7-10 kW. Portable generators can produce enough energy for a few small appliances or lights during an outage.

Standby Generators: Standby generators provide bigger outputs as they draw from natural gas or propane fuel tanks that receive running fuel deliveries from local suppliers. These types generally start up automatically when power is lost due to outage detection hardware installed in your home’s main electrical panel; allowing for continuous power supply for those instances that require it. Standby generators range anywhere from 1KW up to many megawatts depending on the size and purpose; however most residential applications use between 8-20kW models.

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Whole-House Generators: Whole-house generators are designed to provide continuous electricity without interruption and may be warranted by the manufacturer with up to 10 years coverage due thanks in part to its onboard monitoring system which continually checks its own components including oil level, battery levels, cooling systems etc.. They are often connected directly into your home’s natural gas line so fuel delivery is not necessary; however they will still require fresh oil changes periodically just like their smaller counterparts do.. These usually measure between 10kW–50kW depending on what you solar want powered at any given time – making them optimal for large households with several varied electrical needs including hot water heaters and temperature control systems etc..

Pros and cons of each type

Knowing the pros and cons of each type, size, and fuel source can help you make an informed decision about what type of generator is right for your needs.

Portable Generators- These kinds of generators are small and mobile, making them ideal for individuals with smaller power needs. However, they may not provide enough power to support a whole house setup, so it’s important to understand your power requirements beforehand. They tend to be quieter than other types and are usually powered by gasoline or diesel.

Standby Generators- Standby generators provide much more energy than portable generators, making them suitable for larger installations such as whole house setups or industrial operations where running out of power could be catastrophic. This type of generator runs off natural gas or propane and is typically more expensive than other types.

Inverter Generators- These generators offer quiet operation, efficient fuel consumption, and variable power output when compared to traditional portable models. They are often used in campsites or tailgating events due to their lightweight construction and minimal noise output. Inverters typically use gasoline as a fuel source.

Common uses for each type

Residential generators come in a wide range of sizes, so knowing which size is right for your needs is important. Generator sizes are measured in kilowatts (kW) or kilovolt-amps (kVA).

Small Generators: For smaller homes, such as apartments or condos, small generators between 1.5 to 5 kW can provide enough power for essential items like refrigerators and sump pumps.

Mid-Size Generators: Mid-sized generators between 5kW and 16 kW are ideal for medium to large sized homes. These machines can power home essentials, like air conditioners and furnaces during an outage. They’re also perfect for powering large items like microwaves, dishwashers and outdoor lighting systems.

Large Generators: The largest generators are usually used in commercial settings or industrial applications, where power requirements extend over multiple circuits and large equipment such as tools or machinery need to be powered during outages. Large residential generators range from 15 kW to 70 kW or larger – depending on the size of the home, type of appliances being used, and available fuel sources.

Sizing the Generator

Once you’ve identified your power needs, the next step is to size the generator for your home. This process involves calculating how much wattage is needed to run appliances and other electrical equipment during an outage. It’s important to know the average peak demand, which will be higher than the total wattage of all your appliances and equipment. The total wattage necessary should also include a 25–50% buffer in case something comes up that requires extra power.

When you shop for a residential generator, it’s important to pay attention to the size in kilowatts (kW). Generators are available with kW ratings ranging from 7kW–20kW and higher. Consider not only what would be reasonable during a power outage but also what would withstand future growth of electronics and appliances over time. To make sure you are getting an adequate size, refer to the simplified table below that lists common household devices with their estimated average start-up watts:

Determining the appropriate size of the generator

Determining the appropriate size of the generator for a home can be difficult. When buying a residential generator, factors such as how much power you need, the type of fuel used, and the location of your home must all be taken into consideration. To ensure that your generator provides enough electricity for your home’s needs, it is important to consider all of these factors when deciding on the size.

When selecting a residential generator, you must first determine how much power you need in order to power essential household appliances and devices. To determine this amount of power, add up the wattage necessary to operate each device or appliance in your house and then choose a generator that exceeds that total wattage by at least 20%.

You must also consider what type of fuel is best suited to your needs; gasoline-powered, diesel-powered, or propane-fueled generators are available in various sizes. You should also factor in whether you are searching for a portable or stationary type unit and consider any local zoning laws regarding noise levels when shopping for a generator. Additionally, if there are any limitations regarding installation height due to surrounding trees or buildings, this should be taken into account when making your purchase decision.

Matching generator size to power needs

Matching the correct generator size to your power needs is critical. Estimating correctly will ensure a safe operation and optimal efficiency while also avoiding over-sizing, which can lead to higher emissions and additional operating costs. To estimate your power needs, start by identifying the circuits in your home that you want to power during an outage. It’s important to include any computers or other electronics that require voltage stabilization or are sensitive to surges or sags in electricity supply. Also include items such as refrigerators, freezers, microwave ovens, air conditioners, sump pumps, security systems and well pumps.

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Next, look at an electricity usage chart for each appliance you identified (these numbers can be found on the manufacturer’s label) and calculate the total kW rating of all of these appliances added together. This number is a critical starting point when determining the size of an appropriately matched residential generator. As a general rule of thumb, you should purchase a generator rated at least twice as powerful as the total number of kW you calculated earlier. This ensures that your generator can handle fluctuations in demand from items like air conditioners or other appliances with start up motors without tripping on over load low voltage events.

Finally for safety reasons it is always recommended by National Electrical Code Standards to install a transfer switch when running backup generators; this helps prevent backfeeding currents into the utility grid when utility service has been restored after an outage.


In conclusion, installing a residential generator is an important decision and can be a bit overwhelming at first. When choosing the generator that’s right for your needs, you should consider the factors of power output, size, and type. Power output helps to determine how much electricity your generator can provide to various electrical circuits in your home during a power outage. Size will affect both how much energy your generator can provide and how easy it is to install or move around. The choice of electric or gas-powered will depend on the availability of fuel around your area and what type works best for you.

Following these steps will ensure that you make an informed purchasing decision when sizing a residential generator that meets all of your needs. Utilizing this guide in combination with doing some research on retail websites and asking questions from professionals is the best way to ensure that you make the correct selection for your own situation reliably and affordably.

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