When the power cuts out on a 100-degree San Antonio afternoon, the first question most homeowners ask is not, “Do I need a generator,” but, “What size generator do I need so my house actually stays livable?” Losing the lights is annoying. Losing your air conditioning, refrigerator, Wi-Fi, and ability to cook or work from home can make an outage feel a lot more serious, especially if it drags on for hours or days.
Many people start searching for “home generator size San Antonio” hoping to find a simple chart that tells them the exact number of kilowatts they need. Instead, they run into conflicting advice, square-foot rules of thumb, and online calculators that ignore how hard your AC works in our summers. That is frustrating when you are trying to make a big investment and do not want to guess wrong or pay for more generator than you will ever use.
At Absolute Power Electrical Contractors, we have been installing and maintaining home generators in San Antonio, Boerne, and nearby communities since 2005 through our GenCare program. Our licensed electricians size systems for local homes every week, so we see what actually works when the grid drops on a triple-digit day. In this guide, we will walk through how we think about home generator size in San Antonio, using clear examples so you can get a realistic range for your home and know when it is time for a professional load calculation.
What “Right-Sized” Means For A San Antonio Home Generator
Right-sized does not always mean the biggest generator you can afford. For most San Antonio homeowners, the right size is the one that keeps your home comfortable and functional during an outage without forcing you to overspend on equipment or fuel. That usually means choosing between full-home backup and an “essentials plus comfort” approach that covers what you truly need, not every single outlet.
Whole-home backup aims to run almost everything you normally use, including multiple AC systems, electric ranges, dryers, and sometimes pool equipment. This often leads to larger generators that cost more up front and use more fuel when they run. An essentials-only setup might cover a single AC system or a few rooms, your refrigerator and freezer, some lighting, Wi-Fi, and a few key outlets. Many San Antonio families land somewhere between these two extremes, with a generator that runs one main AC system and most day-to-day circuits, while leaving heavy, nonessential loads off-line during an outage.
In our climate, air conditioning is usually the deciding factor in right-sizing. Lights, TVs, and electronics do not draw nearly as much power as a central AC compressor starting up in the afternoon heat. We often meet homeowners who assume their “biggest” loads are in the kitchen, then are surprised when we show them how much of the generator’s capacity is actually dedicated to cooling. Defining what right-sized means for your family starts with deciding how much AC and which circuits you truly want available when the grid is down.
Step 1: Decide What You Want To Power During An Outage
Before we ever talk kilowatts, we talk priorities. The list of what you want to power during an outage drives every sizing decision that follows. For many San Antonio homeowners, the must-haves include at least one central AC system or a high-capacity window unit, refrigerators and freezers, some interior and exterior lighting, Wi-Fi and device charging, and key outlets in bedrooms, a home office, and living areas.
Beyond that core list, there are “nice-to-haves” that may or may not make the cut depending on your budget and how often you lose power. These might include an electric oven and range, microwave, dishwasher, clothes dryer, pool pump, garage door opener, security system, and nonessential receptacles. If you have unique needs, such as a well pump, irrigation system, or a workshop with larger tools, those all need to be considered as well. We also ask how long your outages typically last, because a two-hour blink and a two-day storm outage call for different levels of coverage.
During our in-home generator consultations, we usually walk room to room with homeowners and ask what they actually used or wished they had during their last outage. That conversation often reveals forgotten loads like gate operators, medical equipment, or aquariums. Once you have a clear picture of your must-haves and nice-to-haves, it becomes much easier to decide if you want an essential-circuits setup that feeds a dedicated backup subpanel, or a near whole-home strategy that uses a larger generator and more extensive load management.
In a typical 1,800 to 2,200 square foot San Antonio home, an essentials-only list might include one 3 ton AC system, refrigerator and freezer, some lighting circuits, the garage door, kitchen outlets for a microwave and coffee maker, and outlets for phones and laptops. A near whole-home list might add a second AC system, electric oven, and laundry, which drives you to a larger generator size. Getting these priorities on paper is the first real step toward choosing the right generator size.
Step 2: Understand How Home Electrical Loads Add Up
Once you know what you want to power, the next step is understanding how those loads add up. Every electrical device has a running wattage, which is how much power it uses while operating, and many have a higher starting wattage, which is the brief surge needed to get motors turning or compressors running. Central AC systems, refrigerators, and well pumps are classic examples where starting watts matter just as much as running watts for generator sizing.
For a simple mental model, remember that watts measure power and kilowatts are thousands of watts. Amps and volts combine to make watts, using the basic formula watts = volts x amps. If a device on a 240-volt circuit draws 20 amps while running, that is about 4,800 watts, or 4.8 kW. Many central AC systems fall in a range where running wattage is roughly 3 to 5 kW, with starting surges that can be significantly higher for a few seconds when the compressor kicks on.
It is also important to know that not every load runs at full power at the same time. Electricians account for diversity, which means we recognize that your oven, dryer, and AC are rarely all starting up together at their maximum. That does not mean you can ignore starting loads. It means a properly sized generator has enough capacity to handle typical combinations of running and starting loads without tripping, rather than being sized for a theoretical worst case that almost never happens in everyday use.
A common misunderstanding we see in San Antonio is the idea that your generator size should match the amperage of your main panel. For example, homeowners with a 200 amp service sometimes assume they need a 48 kW generator, because 200 amps at 240 volts is 48,000 watts. In reality, almost no home is drawing that much continuous power. Our founder, a Master Electrician, built our process around code-compliant load calculations instead of raw panel ratings, and our technicians use those same methods every day to determine what size generator truly makes sense for each home.
How San Antonio’s Heat & AC Loads Drive Home Generator Size
In milder climates, homeowners might go through entire outages without running their AC or electric heat, so lighting and refrigeration dominate their backup needs. In San Antonio, the story is very different. When the temperature climbs, keeping at least part of your home cool is often the single most important function of a standby generator. AC systems have large compressors that demand significant power, especially at startup, so they usually occupy a big share of your generator’s capacity.
A typical single-stage 3 ton central AC unit might need in the ballpark of 3 to 4 kW while running, with a higher surge for a few seconds when it first turns on. A larger 4 or 5 ton unit, or a second system serving an upstairs or addition, can push that running load higher. If your home has two systems, powering both at the same time may easily require a generator in the higher end of the residential range, particularly if you also want to run an electric oven, dryer, or other heavy loads at the same time.
More advanced AC systems, such as variable-speed or two-stage units, can have different load profiles. They may draw less power at lower stages but still require careful planning for maximum output and any associated air handlers or electric heat strips. When we size a generator, we look at the actual nameplate ratings on each unit, not just the tonnage, and we plan for realistic usage patterns in San Antonio’s heat. For many homes, that means ensuring the generator can handle starting one AC system and then staggering other large loads so everything runs smoothly without nuisance shutdowns.
Because we work daily with Central Texas HVAC setups and see how they behave on generator power, we know that AC sizing is often where DIY estimates go wrong. Homeowners might add up lights and outlets, end up with a small number, and then be surprised when the generator struggles as soon as the compressor starts. By putting AC loads front and center, you get a much clearer picture of the generator size your San Antonio home truly needs.
Real-World Generator Size Ranges For Typical San Antonio Homes
Once you understand priorities and how loads add up, it helps to see some real-world scenarios. These are not one-size-fits-all prescriptions, but they reflect patterns we see again and again in San Antonio area homes. Seeing where your situation fits can give you a reasonable starting range for home generator size.
Consider a smaller home, roughly 1,400 to 1,800 square feet, with a single 3 ton AC system, gas heat, a standard refrigerator and freezer, and mostly LED lighting. If this homeowner wants essentials-only backup, their list might include the AC, refrigerator and freezer, some lighting circuits, Wi-Fi and outlets in a few rooms, and the garage door opener. The combined running load for that list might fall somewhere around 5 to 7 kW, with starting surges pushing a bit higher. In many cases like this, a standby generator in the 7 to 10 kW range can cover these essentials comfortably when the system is designed correctly.
Now picture a mid-size home, around 2,000 to 2,800 square feet, with one main AC system and several more appliances used regularly, such as microwave, electric oven, dishwasher, and a home office. If the goal is to keep the core of the home feeling close to normal, we might plan to run the AC, refrigerators, kitchen outlets, key lighting, home office circuits, and maybe the microwave or oven, while managing when certain heavy loads run together. These homes often land in a generator size range of roughly 14 to 18 kW, which allows enough headroom for AC starting surges and moderate overlapping use of kitchen and laundry equipment.
For larger homes, particularly those with 3,000 square feet or more and two AC systems, electric water heating, and possibly a pool pump, the picture changes again. If the homeowner wants the ability to run both AC systems and most other loads with minimal adjustment, generator sizes in the 20 kW and above range are typically considered. Some families in this category prefer to prioritize one AC system and select circuits instead, which can allow a slightly smaller generator when paired with load management. In our work across San Antonio and Boerne, we have seen how aligning expectations with these typical ranges helps prevent both disappointment and overspending.
These examples are starting points, not final answers. The exact kW recommendation depends on the specific equipment in your home, how it is wired, your fuel source, and how you actually live during an outage. During an in-home visit, we verify each major load and fine-tune these rough ranges into a precise generator size and configuration that fits your budget and comfort goals.
Why Professional Load Calculations Beat Online Generator Calculators
Online generator calculators can be tempting. You check a few boxes for appliances, enter your square footage, and get a number in seconds. The problem is that most of these tools do not know anything about your actual AC equipment, your panel layout, or how San Antonio outages really play out in the summer heat. They often assume generic wattages, ignore starting loads, and may push you toward a size that is either too small for your AC or larger than you truly need.
When one of our licensed electricians comes to your home, the process looks very different. We start by reviewing your main panel and any subpanels, noting how circuits are grouped and where an essential circuits subpanel or transfer switch would connect. We identify major loads such as HVAC systems, electric water heaters, well or irrigation pumps, kitchen equipment, and any EV chargers or workshop tools. We read the data plates on these devices to get actual voltage and amperage ratings, and we ask detailed questions about what you expect to use and for how long during an outage.
Transfer equipment and load management are also part of the picture. A manual or automatic transfer switch separates your home from the grid when the generator is running, which is important for safety and code compliance. Load management modules can automatically pause lower-priority loads when higher-priority equipment, such as a second AC system, starts. For example, we might configure a system so that the electric oven temporarily drops offline when the upstairs AC kicks on, then comes back once the surge passes. This kind of design can allow a slightly smaller generator to handle a larger home safely and comfortably.
Because Absolute Power Electrical Contractors handles panel upgrades, wiring, and smart home integration as well as generators, we are not just guessing at a generator size and leaving you to figure out the rest. We design the entire backup power system so that the generator, transfer switch, and existing electrical infrastructure all work together. That level of detail is something an online calculator cannot match.
Planning For Future Loads So Your Generator Does Not Fall Behind
Many homeowners size a generator around today’s loads, then call us a few years later after adding an EV charger, a pool, or a new electric range that pushes their system to the edge. San Antonio’s housing stock is evolving, and more homes are picking up higher-demand devices every year. Part of choosing the right home generator size is thinking about how your electrical needs might grow during the life of the system.
Common upgrades we see include electric vehicle charging stations, additional HVAC systems for new rooms or finished spaces, pool and spa equipment, larger refrigerators or freezers, and conversions from gas to electric appliances. Each of these adds running and sometimes significant starting loads. If your generator was sized to just barely cover your original list with no margin, these additions can force you to shut more things off during outages or consider a generator replacement sooner than expected.
When we size a generator, we usually build in a reasonable buffer for future growth. That might mean choosing a size that leaves a few kilowatts of capacity unused in your current configuration, or using load management to free up space for later additions. During your assessment, we will ask about any planned renovations, EV purchases, or pool projects, and we design the system with those in mind. That way, your generator remains a good fit for your home for many years.
Ongoing maintenance and periodic checkups also play a role in keeping your generator aligned with your needs. Through our GenCare generator maintenance program and Absolute Advantage Membership, we perform regular inspections and can revisit your load profile if your home changes. This long-term approach helps keep your generator from quietly falling behind as your lifestyle and electrical usage evolve.
How Absolute Power Electrical Contractors Sizes & Installs Home Generators In San Antonio
Choosing a generator size is one piece of a larger project that includes design, permitting, installation, and ongoing care. Over the years, we have developed a clear process so homeowners know exactly what to expect from the first phone call through the first real-world outage. Our goal is to make a complex electrical project feel straightforward and transparent.
It typically starts with a phone consultation, where we gather basic information about your home, your recent outage experiences, and your goals for backup power. From there, we schedule an in-home assessment. During that visit, our licensed electrician reviews your electrical panels, major appliances, HVAC systems, and any special loads like well pumps or EV chargers. We walk through your must-have and nice-to-have list, talk through budget and fuel options, and perform load calculations based on your actual equipment.
After the assessment, we provide a written estimate that outlines the recommended generator size, brand and model options, transfer equipment, and any panel work needed. We explain in clear language what each size option would realistically power in your home, so you can decide if you prefer essentials-only, near whole-home coverage, or something in between. Our pricing is upfront and transparent, so you can make an informed decision without surprises.
Once you approve the plan, our team coordinates installation, handles necessary permits, and completes all electrical work to current safety standards. We test the system thoroughly, walk you through how it operates, and enroll you in our GenCare maintenance program if you choose. With our Absolute Advantage Membership, you can also receive priority scheduling, annual inspections, and other benefits that keep your electrical system and generator ready for the next storm. As a family-owned company led by a Master Electrician and backed by an A+ BBB rating and strong customer reviews, we take pride in standing behind the systems we install across San Antonio and Boerne.
Find The Right Home Generator Size For Your San Antonio Home
By now, you have seen how many factors go into sizing a home generator in San Antonio, from AC loads in our extreme heat to the specific circuits you care about and the upgrades you may add in the future. Rules of thumb and online charts can give you a rough idea, but a system that truly fits your home and expectations comes from combining your priorities with a careful look at your actual electrical equipment.
If you have a general sense of what you want to run during an outage, the next smart step is a professional load assessment and site visit. Our team at Absolute Power Electrical Contractors can translate your wish list into a clear generator sizing plan, explain what different kW ranges will realistically cover, and provide an upfront estimate for a complete, code-compliant installation and maintenance program. When the next storm rolls through, you will know your backup power was chosen with your home, your comfort, and our San Antonio climate in mind.
Call (210) 981-6868 to schedule your in-home generator sizing consultation.