What size generator do I need?

What is generator size?

Many people never realize how important power is to them until they lose it. If you live in an area with frequent power outages, you understand the inconvenience, discomfort, and insecurity that accompanies a sudden loss of power, especially in harsh climates. As a result, more and more people are investing in backup generators to provide their family with power during outages. When buying a generator, however, it’s important to ask yourself: “What size generator do I need?”

In technical terms, a generator’s size has nothing to do with its physical dimensions. Rather, a generator’s size, also known as its capacity, refers to the amount of power it can produce at a given time to start up and sustain electrical appliances in the home. In other words, a larger generator will produce more power than a smaller one. Size is measured in watts or kilowatts, which are units of electrical output.

On average, a medium-sized home requires a generator with a capacity of 5 to 7 kilowatts. When determining the ideal generator for your home, however, it’s important to be as exact as possible. This article provides an outline for how to estimate the best-sized generator for your home based on your electrical needs. Additionally, you may find AlltimePower’s free Power Calculator helpful in determining the best size generator for your home. The service will also give you a price estimate and match you with reputable generator dealers in your area.  

Why generator size is important

When choosing a generator, there are many factors to consider, from the generator’s fuel source to its brand to its noise cancellation features. A generator’s size, however, may be the most important factor. If the generator size is larger than you need it to be, you may pay thousands of dollars more for the unit than you should have. Larger generators also cost more to run, so you will continue to pay for the oversized generator years after your initial purchase.

On the other hand, if the generator is too small for your needs, you risk overloading the generator. If you force your generator to supply more power than it can handle, the generator will either automatically shut off or it may overheat. Causing the generator to overheat damages the generator’s engine and could also harm the appliances in your home that it was powering. In some cases, overloading a generator could risk starting a fire.

Even if you successfully avoid overloading the generator, buying a generator that is too small for your needs will mean that you have to choose which devices you want to power during an outage. For example, you might have to choose between running the air conditioning unit or water heater. To avoid a situation like that, you should think ahead about which appliances you are willing to do without during an outage and which you want to run.

Calculating your house’s power needs

When calculating your house’s power needs, start by making a list of all the appliances you would want to power during an outage. You may want to make three lists: appliances you would need during an outage (such as heating or air conditioning), appliances you would want to run during an outage (such as a dishwasher or water heater), and appliances you could do without (perhaps the washing machine and dryer). This way, you can determine the approximate size and cost of each level and make the best decision based on your budget and desires.

Next, determine the starting wattage of every item on each of your lists. An appliance’s starting wattage is the amount of power it takes to start it. A common mistake is for homeowners to calculate their power needs based on appliances’ running wattages, or how much it takes to run the item, rather than their starting wattage. However, since it usually takes 2-3 times more power to start an appliance than to run it, it’s wise to use the starting wattage as your baseline, since a generator would need to start all of the appliances in addition to running them.

You can usually find an appliance’s starting wattage printed on a small panel in the back. If not, look for a user’s manual for the appliance in your possession or online. If all else fails, use an online estimate to approximate the appliance’s starting wattage. Once you have at least an estimated starting wattages for each appliance on your lists, add up the starting wattage. This will at least give you an approximation of the size of the generator you need.

Whole-house versus partial-house generators

While some homeowners only want a generator that will allow them to run a select few appliances during an outage, others prefer a whole-house generator that will power all of the appliances at once. Whole-house generators allow you and your household to function as if the power had never been shut off. They thus provide more consistent and reliable power. Homeowners who live in areas with long power outages that may last for days, such as those that live in areas prone to natural disasters, may want a whole-house generator.

To determine the right size generator for your entire house, you’ll need to add up all of the starting wattages of all of the appliances you typically use in a day. As you would expect, a whole-house generator costs more than a partial-house generator. The larger the generator, the higher the price. Nevertheless, the convenience and security of a whole house generator is worth the high price tag to some homeowners.

Partial-house generators only have the capacity to power part of your home. You’ll likely still be able to power important appliances, such as air conditioning or heating, refrigeration, and water heating, but other appliances will have to be sacrificed. This may be a good option if you live in an area with frequent but short power outages, or if you are on a tighter budget.

To keep from accidentally overloading a partial-house generator, consider installing a critical load panel. This piece of equipment controls which appliances receive power from the generator during an outage. For example, a critical load panel might prevent power from going to appliances deemed less important, such as the dryer or dishwasher, in order to ensure appliances such as the water heater or air conditioning have enough power to start up.

How generator size affects cost

When it comes to the cost of installing a backup generator, the biggest determining factor is size. Regardless of a backup generator’s brand or fuel source, a higher capacity requires a more complicated and powerful engine, which will increase the price. Additionally, larger generators require more fuel and may need additional maintenance, which would add to the overall cost. The high price tag that comes with larger generators is one of the reasons why it is so important to make sure you buy the right sized generator for your home.

Generally, larger homes have greater electrical needs. In some cases, however, certain electrical devices in smaller homes may greatly increase the home’s electrical needs. For example, a smaller home in a cold climate that requires a lot of heating may require a greater electrical capacity than a larger home in a more temperate climate. Similarly, a smaller home with outdated or inefficient electrical appliances may require a larger generator than a larger home with appliances that use energy more efficiently.

As a result, updating your electrical appliances before purchasing a generator may help you cut down on the cost. Alternatively, you might be able to buy a smaller and less expensive generator if you and your family can minimize your electrical usage during power outages. If you plan to do this, write down an electrical usage plan for outages that includes how much power you are likely to use, and make sure you and your family can follow it. For example, by minimizing shower time or washing dishes by hand, you might be able to reduce your electrical usage during an outage.

Installing the right sized generator

Sizing a generator yourself or through an online power calculator is a good way to narrow your search for a generator and understand how much you can expect to pay. Before making a purchase, however, you should consider hiring a professional electrician to make a more exact calculation as to the size of the generator you need. Doing so will cost a little money, but it is an investment worth paying for considering the high cost of installing a generator. He may save you a lot of money in the long run by preventing you from purchasing the wrong sized generator.

Once you’ve determined the right sized generator for your home, you can start considering other factors that are important to you. For example, you should consider which fuel source you want your generator to run on, as well as what noise-canceling features you want the generator to include. If you use AlltimePower’s backup generator pricing tool, you’ll receive cost estimates based on the features that are important to you. You’ll also have the option to have reputable generator dealers in your area compete to give you the best price.

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