How To Know What Size of Whole-home Generator You Need

Standby or whole-home generators can be a huge help by ensuring that your home will still have electricity should the power ever go out. These units are different from portable generators in that they are wired directly into your home’s electrical system. In the event of a blackout, the generator will automatically turn on so that you can keep your refrigerator and freezer cold, run your HVAC system, and use all of your lights and power outlets. However, it is vital that you choose a generator that is large enough to meet all of your energy needs. If the generator is too small, it won’t ever work as it will always get overloaded and automatically shut down. To ensure this doesn’t happen, here is a full overview of exactly how to calculate what size of whole-home generator you need.

Calculating Your Energy Needs

When deciding which generator to buy, the first thing you’ll want to do is make a list of every appliance and device you think you may need during a power outage and how much energy each one uses. This can include things like your refrigerator, freezer, microwave, TV, computer, washer and dryer, electric water heater, etc. You will also want to count all of the lightbulbs in the house and how many watts each uses to ensure that you can still power your lighting. Once you have your list, you can add up the energy usage of all of your appliances and devices to calculate how much electricity your generator would need to produce to power everything you need.

Most whole-home generators allow you to prioritize certain loads or appliances/systems. This means that the generator will always supply power to those things first, and then only power the lower-priority loads if there is enough remaining electricity. This is known as load management, or load shedding, and is important for preventing the generator from potentially being overloaded and shutting down.

You can also isolate certain circuits so that the generator will never power them. For instance, if you don’t think you would need your microwave during a blackout, you can set it up so that the circuit it is on doesn’t receive any power.

Why Your AC Is the Main Factor To Consider When Sizing a Generator

Performing a load calculation is always important. However, if your home has central air conditioning, the main thing you should focus on when sizing a generator is the size of your AC unit. This is because your air conditioner uses far more electricity than anything else in the home, and it requires even more energy during the few seconds when it first starts up.

Let’s say you have a 15 SEER 2-ton AC. This unit will use around 1.6 kWh (kilowatt-hours) of electricity whenever it is running. However, the AC will typically need anywhere between 3 and 6 kWh of electricity in order to turn on, plus around 1 to 1.5 kWh extra to start the HVAC blower fan. This means you may need at least a 7.5 kWh generator just to ensure that you have enough electricity to power your air conditioning, and this still doesn’t take into account all of your other electricity needs. If your AC is only 13 or 14 SEER, then you would need an even larger generator.

To ensure that you have enough power for your AC and your other important appliances, it is generally recommended that you choose around an 11 kWh generator if you have a 2-ton AC. If the generator is smaller than this, it may need to shut off the power to some of your other appliances every time your AC needs to start.

For a 3-ton generator, you will typically need a 14 kWh generator. This recommendation increases by 3 kWh for every additional AC ton i.e. a 4-ton generator typically needs a 17 kWh generator and a 5-ton AC needs a 20 kWh generator.

Understanding Load Management and Load Shedding

If you have a 2-ton AC and an 11 kWh generator, your AC and blower fan will use up much of the available energy during those few seconds when your cooling system first starts running. This means that there may not be enough remaining energy available to also power your refrigerator, lighting, etc. If the generator were to continue powering everything at once, the additional electricity drawn from when your AC first starts would result in the generator overloading and automatically shutting down.

This is where load management and load shedding come into play. Load management means that everything is assigned a priority, and those with the highest priority are always powered first. Since your AC uses more energy than anything else, it always has the highest priority. Whenever the cooling system needs to turn on again, the generator will temporarily transfer power away from the lower priority loads to ensure there is enough electricity for the AC and blower fan to start, and this is known as load shedding.

As with your air conditioner, most other major appliances like refrigerators and electric water heaters also require somewhere around two to four times more electricity when first turning on than they do when running. If your refrigerator remains closed, it will typically run one cooling cycle every two or three hours and each cycle usually lasts around 30 to 40 minutes. Every time a new cooling cycle starts, the refrigerator will require much more energy at first in order to power the compressor motor.

If the generator tried to turn the AC, refrigerator, and everything else in the home on at the same time, it would easily become overloaded. Load management and shedding ensure that this won’t happen. When the generator first starts, it will always power your lighting and turn on your AC or heating if needed. Once the HVAC system is running, the generator will power the refrigerator and then supply power to your outlets and other lower-priority appliances. Whenever the AC needs to turn on again, the generator will shed some loads to ensure it is never overloaded.

Load management and shedding are important as they enable you to go with a smaller generator than you may otherwise need. Without these features, you would often need up to a 15 kWh to power a 2-ton AC and everything else, and up to a 25 kWh generator to power everything in a home with a 5-ton AC unit.

Expert Electrical and Plumbing Services

If you’re considering a whole-home generator, the professional electricians at AJ Danboise Plumbing, Heating, Cooling & Electrical can help you perform a load calculation to determine exactly what size of unit you need. We specialize in whole-home generator installation, as well as repairs and maintenance. Our team can also help with whole-home surge protection, lighting, outlets, ceiling fans, electrical panel replacement, and electrical repairs. We have a team of licensed plumbers to assist with drain cleaning, in addition to water heater, sump pump, garbage disposal and water filtration installation, and repair and maintenance services. Give us a call today to learn more about whole-home generators or if you need any electrical or plumbing services in the Farmington Hills area.

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