Generator size depends on which appliances and systems you want to keep running during an outage. A small portable generator (3,000 to 5,000 watts) covers essentials like a refrigerator and a few lights, while a mid-size unit (7,000 to 10,000 watts) can handle more circuits, and a whole-home standby generator (17,000 watts or more) can power an entire house, including HVAC systems, without interruption.
Getting the size right matters, especially in Texas, where extreme summer heat and occasional severe weather make reliable backup power more than just a convenience.
Understanding Your Power Needs
Start With What You Actually Need to Run
The first step in sizing a generator isn’t picking a wattage number, it’s making a list of what you want powered during an outage. This might include a refrigerator, a few lights, a sump pump, a window AC unit, or in some cases, your entire HVAC system and every major appliance in the house.
Once you have that list, you can add up the approximate wattage each item needs to run, plus a bit extra for the higher starting wattage many appliances require when they first switch on.
Essential Circuits vs. Whole-Home Coverage
There’s a meaningful difference between covering essential circuits and covering your entire home. Essential circuit coverage typically includes refrigeration, some lighting, a sump pump if you have one, and maybe a window unit or space heater. Whole-home coverage means every circuit in your panel stays live, including central air conditioning, which draws significantly more power than most other household systems combined.
Generator Types and Typical Sizing
Portable Generators (3,000 to 8,500 Watts)
Portable generators are a common choice for homeowners who mainly want to keep essentials running during shorter outages. They’re more affordable upfront and don’t require a permanent installation, but they do need to be manually connected and fueled, and they won’t handle whole-home HVAC loads.
Mid-Size Standby Generators (10,000 to 16,000 Watts)
These units bridge the gap between basic essentials and full-home coverage. They can typically handle a window or small central AC unit alongside most household circuits, making them a solid fit for homes that want more than the basics without paying for full whole-home capacity.
Whole-Home Standby Generators (17,000 Watts and Up)
Whole-home generators are permanently installed, run on natural gas or propane, and automatically switch on within seconds of a power outage. These are designed to power an entire home, including central air conditioning, without any noticeable interruption in daily life.
How to Calculate Your Wattage Needs
A simple way to estimate your needs is to list your essential appliances alongside their running wattage, which is usually listed on the appliance itself or in its manual. Add these numbers together for your baseline running wattage. Then account for starting wattage, since motors in appliances like refrigerators, sump pumps, and air conditioners briefly draw more power when they first turn on, sometimes two to three times their running wattage.
A rough guide for common household items:
- Refrigerator: 600 to 800 running watts
- Window AC unit: 1,000 to 1,500 running watts
- Central AC (varies by size): 3,000 to 5,000+ running watts
- Sump pump: 750 to 1,500 running watts
- Lighting circuits: 60 to 600 watts depending on how many fixtures
- Microwave: 600 to 1,200 running watts
Adding these up, along with a buffer for startup surges, gives you a realistic target wattage to look for in a generator.
Why Central Air Conditioning Changes the Equation
Central AC is one of the biggest power draws in a typical Texas home, and it’s often the deciding factor in whether a homeowner needs a mid-size unit or a full whole-home standby system. If keeping your AC running through a summer outage matters to you, and in Texas heat, it often does, this pushes most homeowners toward the higher end of generator sizing.
Fuel Type Considerations
Portable generators typically run on gasoline, which requires manual refueling and on-site storage. Standby generators usually run on natural gas or propane, connecting to an existing gas line or a dedicated propane tank, which means they don’t run out of fuel the way a gasoline-powered unit can during an extended outage. This is worth factoring in if you’re comparing options for longer power outages, which aren’t uncommon during severe Texas weather events.
Common Sizing Mistakes to Avoid
One of the most common mistakes is undersizing a generator by only accounting for running wattage and ignoring the higher startup wattage that motors require. This can cause a generator to overload and shut down right when you need it most. Another common mistake is failing to account for future needs, like adding central AC to the load calculation years down the road after upgrading a portable unit that was originally sized for just the basics.
Comparing Generator Options Side by Side
Looking at the three main categories together often makes the decision clearer. Portable generators offer the lowest upfront cost and no permanent installation, but require manual setup and fueling every time they’re used, and they can’t handle whole-home HVAC loads. Mid-size standby units offer a meaningful step up, covering more circuits and sometimes a smaller AC unit, with automatic switching that portable units don’t offer. Whole-home standby generators cost more upfront but deliver true set-it-and-forget-it reliability, automatically restoring full power, including central air, within seconds of an outage.
How Home Size and Layout Affect Sizing
A larger home with more circuits, multiple HVAC zones, or a bigger electrical panel generally needs a higher-capacity generator than a smaller home with a single AC unit and standard appliance load. Homes with additions, finished garages, or workshops with dedicated circuits also tend to need more capacity than the base square footage alone would suggest. This is another reason a professional load calculation, rather than a generic size chart, tends to produce a more accurate recommendation.
What a Licensed Electrician Evaluates During a Generator Consultation
Standby generators require professional installation, including a transfer switch that safely disconnects your home from the grid during an outage and prevents dangerous backfeed into utility lines. This isn’t something to handle without a licensed electrician, both for safety reasons and because most manufacturers require professional installation to maintain the warranty.
A licensed electrician can also do a more precise load calculation specific to your home’s electrical panel and appliances, rather than relying on general estimates. If you’re considering a generator for your home, our team can walk you through sizing and installation as part of our electrical services in Hutto and the surrounding area.
Planning for Seasonal Texas Weather
Texas homes face a fairly wide range of outage scenarios, from summer storms and heat-driven grid strain to occasional winter freezes. Sizing a generator with these different scenarios in mind, rather than just the most recent outage you experienced, tends to give a more realistic picture of what you’ll actually need long-term. A generator that comfortably handles a mild fall outage might fall short during a July heatwave when your AC is working overtime alongside everything else in the house.
Maintenance Considerations After Installation
Once a generator is sized and installed, regular maintenance keeps it ready when you actually need it. Standby generators typically run brief self-test cycles automatically, but they still benefit from periodic professional inspection to check oil levels, battery condition, and overall function. Skipping this maintenance is one of the more common reasons a generator fails to start during an actual outage, even when it was properly sized in the first place.
FAQ
What size generator do I need to run my whole house?
Most whole-home coverage, including central AC, requires a standby generator rated at 17,000 watts or higher, though the exact size depends on your home’s specific electrical load.
Can a portable generator run my refrigerator and a few lights?
Yes, a portable generator in the 3,000 to 5,000 watt range typically covers a refrigerator, some lighting, and a few small appliances.
Do I need a professional to install a standby generator?
Yes, standby generators require a transfer switch and proper electrical connections that should always be installed by a licensed electrician for safety and warranty reasons.
What’s the difference between running watts and starting watts?
Running watts is the power an appliance needs during normal operation, while starting watts is the higher, brief power draw needed when a motor first turns on.
Can I add central AC to a generator I already own?
It depends on your existing generator’s capacity. If it wasn’t sized to include AC originally, you may need to upgrade to a larger unit rather than simply adding the load.
