Backup power planning is essential to staying safe and comfortable during outages. Proper generator sizing is critical for energy efficiency, reliability, and safety. You need a generator that can handle modern appliance loads and extended power outages. Under-sized generators often fail under high loads during storms.
Schedule a backup power consultation with MyReliablePower to make sure you get the right size generator. Read this generator sizing guide to learn how to find the right whole-home generator size.
Step 1: Identify Your Essential Household Loads
The first step to generator sizing is to identify your essential loads. Essential loads are the appliances or systems your home will need to run during an outage. It’s important to make a list of everything you need to power, aka an essential loads list.
This can include categories, such as:
- HVAC equipment (furnace blower, AC condenser)
- Refrigerators and freezers
- Well pump or sump pump
- Lighting and outlets
- Medical devices
- Internet equipment for work-from-home needs
List everything you might need your generator to power. Then, you can whittle it down to a priority list.
How to Make a Priority List
Create a priority list of your “must run” appliances and systems and separate your “nice to haves” out. To make a priority list, think about the bare minimum systems you need to stay safe and comfortable at home.
For most people, your priorities are most likely your HVAC equipment, a fridge and freezer, lighting, and a well or sump pump (if applicable). Internet equipment may be necessary if you run a business or work from home. Thinking in terms of what you actually need vs. what you can live without can impact generator sizing dramatically.
Step 2: Calculate Running Watts vs. Starting Watts
Running watts are the continuous load a generator will need to carry to operate an appliance or system. Starting watts are the surge of extra power it takes to start appliance with motors, such as AC compressors, refrigerators, and sump pumps.
To calculate running watts and starting watts, read the appliance labels. Starting watts are more important than running watts for generator sizing because certain appliances need a massive power surge to start. If you don’t take this into account when sizing for a generator, you may be left without critical appliances.
How to Read Appliance Labels
You can typically find wattage information on appliance labels. Look for running watts (RW) and surge or starting watts (SW).
Here are some general wattage ranges for common appliances:
| Appliance | Wattage Range |
| Refrigerator | 100–800 W |
| Air conditioner | 500–3,500 W |
| Electric oven | 2,000–5,000 W |
| Space heater | 750–1,500 W |
Step 3: Add Up Your Total Power Requirements
Next, you will need to calculate your total power requirements to determine the required wattage for your new generator. You will need to add together all essential running watts and the highest single starting watt requirement. Then, add a 20-30% buffer for safety.
Here’s a sample calculation:
- List essential loads:
- Air conditioner – 3,500 W (5,000 starting watts)
- Refrigerator – 800 W (1,200 starting watts)
Sump pump – 1,000 W (2,000 starting watts)
- Microwave – 1,200 W (no additional starting watts)
- Lights (multiple rooms, LED) – 400 W
- Add total running watts: 3,500 + 800 + 1,000 + 1,200 + 400 = 6,500 running watts
- Identify and add highest starting watt requirement: The air conditioner has the highest starting watt requirement of 5,000 W.
So, 6,500 + 5,000 = 11,500 W.
- Add a safety buffer: Add a 20-30% buffer for safety.
So, 11,500 x 0.25 = 2,875. Then add them together. 11,500 + 2,875 = 14,375 W.
For this specific example, a 15,000 W or 15 kW generator is an adequate size for their needs.
Step 4: Consider Fuel Type and Run Time
Next, you should consider what fuel type you want for your generator. The primary types of fuel are:
- Natural gas
- Propane
- Diesel
Whole-home generators typically use natural gas or propane because they are reliable, efficient, and suitable for prolonged outages. However, your generator must have access to a gas line for natural gas operation or a large, on-site propane tank.
Natural gas generators connect directly to a utility gas line to provide a consistent fuel source during extended power outages. Natural gas and propane burn cleaner and more efficiently than diesel or gasoline. This makes them better for the longevity of your generator.
Step 5: Determine Whether You Need a Whole‑Home or Partial‑Home System
Once you’ve determined your power needs, you can decide whether a whole-home or partial-home generator is ideal. A smaller partial-home system may not be enough if your home relies on several high-wattage systems for daily operation.
Consider your home size and the number of circuits and appliances, when deciding on a generator. Larger homes with larger family sizes have greater power demands than a single person living in a smaller home.
Heating and cooling systems are typically the largest draw of power in a home. Some central air systems, heat pumps, or furnaces exceed the capacity of smaller generators upon startup.
Benefits of Whole‑Home Backup Power
If you want to operate normally during an outage and not choose which appliances to use, whole-home backup power is vital. The benefits of a whole-home generator include improved comfort and safety, and avoidance of spoiled food or frozen pipes.
Step 6: Evaluate Electrical Panel and Transfer Switch Requirements
Homeowners should evaluate their home’s electrical panel and transfer switch requirements before buying a generator.
Check your existing electrical panel capacity to ensure it has sufficient capacity for a generator. An electrical professional can ensure code compliance and safety standards are met when installing a generator.
A transfer switch must be sized to match your generator’s output and the number of circuits or loads you plan to power. Transfer switches connect your generator to your electrical system and also prevent backfeeding into utility lines.
Request a generator sizing consultation!
Professional Generator Sizing vs. DIY Methods
While home generator sizing can be OK, there are some risks of self-sizing, including:
- Overloading
- Inefficiency
- Damage to appliances
Working with a professional electrician for load calculations ensures your home is protected from the risks of self-sizing. A professional evaluates real-world operating conditions, like seasonal HVAC demands, load diversity, and whether appliances are likely to run simultaneously.
Why Homeowners Choose MyReliablePower
South Florida homeowners trust MyReliablePower for whole-home generator services. Our certified generator technicians bring years of experience and knowledge. With us, you’ll get accurate load calculations, seamless generator installation, and reliable maintenance. We also offer emergency support for extreme weather so you can rest assured you’ll be protected from storms.
Schedule Your Backup Power Consultation
Need help with home generator sizing? Get a professional load calculation to ensure your generator can meet your family’s needs. With MyReliablePower, you can stay safe, comfortable, and prepared.
Call us today at 888-960-4553 to schedule an appointment! Proudly serving Broward, Martin, Palm Beach, Collier and other surrounding areas.
