In our post, “Why a Generator Could Be Your Best Home Improvement Move,” we established that a generator is almost always a financial win. That is, its cost is usually recouped through loss prevention and added home value. Now that you’ve decided to invest in one, the next logical question is, “What size of generator do I need?” In this article, we give some guidelines to help answer that question.
Generators come in a range of power ratings, measured in kilowatts (kW), which determine how many devices or systems they can keep running. Choosing the right size might seem complicated, but it’s easy when you break it down. Follow these steps to find your perfect fit.
” Think of the load on your generator like the weight of a trailer to a tow vehicle: a small sedan might pull a trailer on flat ground, but it won’t handle hills or starts from a dead stop like a truck will.
An undersized generator will burn out during periods of high demand as easily as the small sedan’s engine if it is forced to tow up a long hill. “
Step 1: What Needs to Stay Powered On During an Outage?
Start by listing the devices and systems you can’t live without when the power goes out. This boils down to essentials versus conveniences. For example:
- Do you need your garage doors to avoid being locked out?
- Is powering your fridge critical to save groceries?
- Will your furnace, sump pump, or Wi-Fi be necessary to stay comfortable or connected?
Here’s the list we made for our home:
- Garage doors
- Refrigerator
- Freezer
- Furnace
- Wi-Fi
- Microwave
- Family room circuits (TV, stereo, chargers, etc.)
- Air conditioning
- Key outlets for lamps, hair dryers, and other personal items
If we had a sump pump, it would be a top priority (#2 on the list) to prevent basement flooding. Think about what matters most for your household and jot it down.
Step 2: How Much Power Does Each Device Need?
Next, figure out how much power each item on your list will draw, especially during startup. Devices often use more electricity when turning on than when running. These peak power needs are usually listed as “starting watts” on an appliance’s label. If they are not listed, you can usually contact a manufacturer’s customer service phone or online chat to find out. You can also find ballpark figures through an internet search.
- Garage doors: 700W while lifting
- Refrigerator: 800W to start
- Freezer: 800W to start
- Furnace: 1000W peak for the igniter and fan
- Wi-Fi: 10W with little variation
- Microwave: 1200W when in use
- TV: 200W (older LCD), Stereo: 100W, LED lighting: 10W per bulb
- Air Conditioning: 2200W
If you’re unsure, it’s better to round up to avoid underestimating your needs. Keep in mind that entire circuits (like your family room or kitchen) will likely need to be transferred to the generator, not just individual devices. Also keep in mind that installing all LED bulbs and modern appliances in your home will reduce demands on (and therefore the size of) your generator.
Step 3: Which Devices Will Run Together?
Not everything on your list will need to run all at once. For instance, your furnace and AC aren’t needed simultaneously. However, other combinations—like the fridge, freezer, and Wi-Fi—are more likely during an outage.
Let’s say the power goes out on a summer evening. The kids are streaming movies on the TV while you’re microwaving popcorn. Dad comes home, and the garage door opens. At that moment, you’re running:
- Garage door: 700W
- Fridge: 800W
- Freezer: 800W
- Wi-Fi: 10W
- Microwave: 1200W
- TV: 200W
- Air Conditioning: 2200W
That totals 5910 watts, or just under 6kW. But if you wanted to add a coffee maker, computer, or extra lighting, you could easily exceed that number.
Step 4: Add a Safety Margin
Your generator needs to handle the peak power demand of your household, plus a little extra to manage multiple startups at once. Think of the load on your generator like the weight of a trailer to a tow vehicle: a small sedan might pull a trailer on flat ground, but it won’t handle hills or starts from a dead stop like a truck will. An undersized generator will burn out during periods of high demand as easily as the small sedan’s engine if it is forced to tow up a long hill.
Keeping this in mind, we doubled our estimated wattage and installed a 12kW generator for our home to ensure reliable performance. If making these power tradeoffs isn’t your thing, consider a whole-home generator. These larger systems, typically 20kW or more, can handle every circuit in your house. Or, you may consider a managed load option, available on modern standby power systems. These systems cover all your home’s circuits but cut any non-essential ones when your generator is experiencing peak load. This allows you to protect your whole home more efficiently and cost-effectively with a smaller generator.
The Bottom Line
The right size generator depends on what you’re willing to live without during a power outage. A smaller generator can handle the essentials, while a whole-home system powers everything seamlessly, and a managed load option gives you something in between. Whatever you choose, investing in the correct size will ensure peace of mind when the lights go out.
Still have questions about the size of generator that you need? Schedule a free consultation with us. We will be happy to guide you to the best solution for your home.
