How Many Watts Do You Really Need for Backup Power?
How Many Watts Do You Really Need for Backup Power? Don’t Get Left in the Dark (or Pay Too Much)
Power outages are an inconvenient reality, whether caused by severe weather, grid issues, or unforeseen events. When the lights go out, having a reliable source of backup power can mean the difference between simple discomfort and significant disruption, potentially even danger. But for many, the biggest hurdle isn’t deciding to get backup power, but figuring out how much power they actually need. Enter the confusing world of watts, starting watts, and running watts.
This guide will demystify the process and help you calculate the wattage you really need for your backup power solution, whether it’s a portable generator, a standby system, or a portable power station. Getting the size right is crucial – too little power and your essential appliances won’t run; too much and you’ve wasted money on unnecessary capacity and fuel consumption.
Understanding Watts: Running vs. Starting
Before we dive into calculations, let’s clarify the fundamental concepts:
- Running Watts (Rated Watts): This is the continuous power an appliance needs to operate after it has started up. Think of it as the steady-state power requirement. Your refrigerator hums along using running watts; a light bulb requires running watts to stay lit.
- Starting Watts (Surge Watts): This is the extra burst of power many motor-driven appliances need just for a few seconds to start up. Appliances with motors, like refrigerators, freezers, air conditioners, well pumps, and power tools, typically require significantly more power to get going than they do to run continuously. This surge can be two to three times (or even more) than their running wattage.
Why This Distinction Matters for Backup Power:
Your backup power source (like a generator) needs to be able to handle both the total running watts of all the appliances you want to run simultaneously and the single largest starting wattage requirement of any appliance you might turn on while others are already running.
If your generator only meets the running watt total, it will likely stall or trip a breaker when an appliance with a high starting watt requirement tries to kick on.
The Crucial Calculation: Step-by-Step
Figuring out your actual wattage needs involves a simple, yet critical, process:
Step 1: Identify Your Essential Appliances
Think about what you absolutely must run during a power outage. This isn’t about running everything in your house, but prioritizing survival and comfort. Common essentials include:
- Refrigerator/Freezer (to preserve food)
- Sump Pump (if you live in a flood-prone area)
- Furnace Fan (for heat in winter – often requires significant starting watts)
- Lights (strategically placed LED or energy-efficient bulbs)
- Medical Equipment (CPAP machines, oxygen concentrators, etc. – critical!)
- Phone/Device Chargers
- Basic Cooking Appliance (microwave, hot plate – check wattage!)
- Maybe a Fan or small AC unit (for cooling in summer)
- Well Pump (if you rely on a well for water)
- Garage Door Opener
Step 2: Find the Wattage Requirements for Each Appliance
This is the most time-consuming step but crucial for accuracy. For each item on your essential list, find its running watts and, if applicable, its starting watts.
- Check the Appliance Label: Look for stickers or plates on the appliance itself, usually near the power cord or on the back/side. This often lists "Watts," "Amps," or "Volts." If it lists Amps and Volts, you can calculate watts: Watts = Amps x Volts. (Most household circuits are 120V or 240V). The label might list both running and starting watts, but often only lists maximum draw or running watts.
- Consult the Owner’s Manual: The manual is an excellent resource for detailed power consumption.
- Check the Manufacturer’s Website: Search for the specific model number online.
- Use Online Wattage Charts: Many websites provide estimated wattage requirements for common appliances. Be cautious: These are estimates! Your specific model might vary significantly. Use these as a guide, but prioritize the information from your actual appliance/manual.
- Measure (Optional but Accurate): For the most precise needs, you can use a power meter (like a Kill-A-Watt device) to measure the actual running and starting draw of your appliances under normal conditions.
Example Wattage Estimates (Use as a Guide Only!):
| Appliance | Running Watts (Estimate) | Starting Watts (Estimate) |
|---|---|---|
| Refrigerator (standard) | 600 – 800 | 1200 – 2400 |
| Freezer (standard) | 500 – 700 | 1000 – 2100 |
| Furnace Fan (med-high) | 400 – 800 | 1000 – 2500 |
| Sump Pump (1/2 HP) | 800 – 1000 | 1500 – 2000 |
| Well Pump (1/2 HP) | 800 – 1200 | 2000 – 3000+ |
| Microwave (med-size) | 800 – 1500 | – (Resistive load) |
| Lights (LED) | 5 – 20 per bulb | – |
| Lights (Incandescent) | 60 – 100 per bulb | – |
| TV | 50 – 200 | – |
| Computer (Desktop) | 100 – 300 | – |
| CPAP Machine | 30 – 60 | – |
| Phone Charger | 5 – 20 | – |
Note: Resistive loads like lights, heaters, and microwaves typically do not have significant starting watts.
Step 3: Calculate Your Total Running Watts
Add up the running watts for all the essential appliances you plan to run simultaneously.
Example Calculation:
Let’s say your essential list includes:
- Refrigerator: 700 Running Watts / 2000 Starting Watts
- Furnace Fan: 600 Running Watts / 1800 Starting Watts
- Five LED Lights: 50 Running Watts total (5 x 10W)
- Phone Charging: 10 Running Watts
Total Running Watts = 700 (Fridge) + 600 (Furnace) + 50 (Lights) + 10 (Phone) = 1360 Running Watts
Step 4: Identify the Highest Starting Watt Requirement
Look at your list and find the single appliance with the highest starting watt requirement. In our example:
- Refrigerator: 2000 Starting Watts
- Furnace Fan: 1800 Starting Watts
The highest starting requirement is 2000 Watts (for the refrigerator).
Step 5: Calculate Your Minimum Required Wattage
Your minimum required wattage is the sum of your Total Running Watts plus the Highest Starting Watt Requirement.
Minimum Required Wattage = Total Running Watts + Highest Starting Watt Requirement
Minimum Required Wattage = 1360 Watts + 2000 Watts = 3360 Watts
Step 6: Add a Buffer
It’s wise to add a 10-20% buffer to your calculated minimum. This accounts for minor inaccuracies in wattage estimates, allows for adding a small non-essential item later, and prevents the generator from constantly running at maximum capacity, which can shorten its lifespan.
Adding a 15% buffer to our example:
3360 Watts * 1.15 = ~3864 Watts
Conclusion of the Calculation: For this example scenario, you would need a backup power source with a running wattage capacity of at least 1360 watts and a starting wattage capacity of at least 3864 watts (or higher) to comfortably power these essentials. When shopping for a generator, you’ll look for models that list both ratings. The "peak" or "surge" wattage should meet or exceed your calculated highest starting requirement, and the "running" or "continuous" wattage should meet or exceed your total running requirement.
Different Levels of Backup Power (By Wattage)
Understanding these typical ranges can help you ballpark your needs:
- 1000 – 2000 Watts: Suitable for basic essentials like lights, phone charging, maybe a fan or TV, and potentially a small refrigerator (check starting watts carefully!). Often covered by smaller portable inverter generators or portable power stations.
- 2000 – 4000 Watts: Can usually handle a refrigerator/freezer, lights, phone charging, maybe a microwave or coffee maker, and potentially a sump pump or smaller furnace fan. A common range for mid-size portable generators.
- 4000 – 6000 Watts: Likely capable of running a refrigerator, freezer, multiple lights, chargers, a microwave, TV, furnace fan, and maybe a well pump or a small window air conditioner. This is a versatile range for many homes needing essential-plus backup.
- 6000 – 8000 Watts: Can typically handle most essential loads listed above, plus perhaps a larger well pump, a larger furnace/AC fan, or a couple of window AC units. Getting into larger portable or smaller standby generator sizes.
- 8000+ Watts: Moving towards powering larger homes, multiple large appliances simultaneously (like central air conditioning, electric water heaters, ovens – though electric heat and ovens are very power-hungry), or running a significant portion of the house. Often requires larger portable generators or dedicated standby generator systems connected via a transfer switch.
Important Considerations Beyond Wattage
While wattage is key, other factors influence your choice:
- Type of Backup Power: Portable generators (gas/propane), Inverter Generators (quieter, cleaner power for electronics), Portable Power Stations (battery-based, quiet, no fuel), Standby Generators (permanently installed, automatic).
- Fuel Type/Source: Gasoline, propane, natural gas, diesel, battery. Availability and storage are factors.
- Runtime: How long can the source power your load on a tank of fuel or a charge?
- Noise Level: Especially important in residential areas. Inverter generators and battery systems are quieter.
- Cleanliness of Power: Sensitive electronics (computers, smart TVs) prefer the stable "clean" power from inverter generators or portable power stations.
- Budget: Wattage directly impacts cost.
- Safety: Proper ventilation for generators (carbon monoxide risk!) and safe connection methods (extension cords or a transfer switch installed by an electrician).
FAQs
- Q: Can I just plug everything into a power strip and then into the generator?
- A: You can, but you must ensure the total running watts plus the largest starting watt requirement doesn’t exceed the generator’s capacity. Overloading is dangerous and can damage the generator or your appliances. Use heavy-duty, outdoor-rated extension cords for individual appliances.
- Q: Do I need a transfer switch?
- A: A transfer switch (manual or automatic) is the safest and most convenient way to connect a generator to your home’s electrical panel. It prevents backfeeding power onto the utility lines (which can be fatal to utility workers) and allows you to power hardwired appliances like furnaces and well pumps without running multiple extension cords. It is highly recommended, especially for larger generators powering multiple circuits.
- Q: What happens if I try to run too much?
- A: The generator’s circuit breaker will likely trip, shutting off power. Repeated overloading can damage the generator’s components.
- Q: Are wattage charts online accurate?
- A: They are good estimates but can vary. Always check your specific appliance labels or manuals for the most accurate information. Different models of the same appliance can have different power draws.
- Q: What about my central air conditioning?
- A: Central AC units have very high starting wattage requirements, often thousands of watts. Powering central air typically requires a very large portable generator or a dedicated standby generator system (often 7,000 watts or more). It significantly increases your power needs and budget.
- Q: Is it better to overbuy on wattage?
- A: A small buffer (10-20%) is good. Significantly overbuying means higher initial cost, more fuel consumption (generators are less efficient at very low loads), and potentially a bulkier, louder unit than you need. Size appropriately based on your calculated needs.
Conclusion
Determining how many watts you need for backup power isn’t guesswork; it’s a calculated decision based on your specific needs and priorities. By making a list of your essential appliances, finding their running and starting wattage requirements, and doing the simple math (Total Running Watts + Highest Starting Watts + Buffer), you can arrive at an accurate estimate of the generator or power source size you need.
Taking the time to properly size your backup power ensures you have reliable electricity when the grid goes down, protects your appliances from overloaded circuits, and helps you make a cost-effective investment. Don’t wait for the next outage; plan now to stay powered up safely and efficiently.
