Generator sizing is the question that determines everything else — brand, model, installation complexity, and long-term performance. Get it right and you have a system that handles every outage without strain. Get it wrong and you’re either shedding loads during a storm or paying for capacity you never need.
This guide explains how sizing works, gives you a practical starting point by home size, and explains why the final answer requires a professional load calculation specific to your home.
The Basics: What Generator Size Means
Generator capacity is measured in kilowatts (kW). This number tells you the maximum electrical load the generator can handle simultaneously.
Your home’s electrical demand isn’t constant — it varies throughout the day based on what’s running. Generator sizing is about matching the generator’s output to your peak simultaneous load: the maximum your home draws when the most equipment is running at once.
A common mistake is sizing to average usage rather than peak. On a hot Texas summer day with the air conditioner, refrigerator, lights, and water heater all drawing at the same time, your peak demand is significantly higher than your average.
Starting Point: kW Range by Home Size
| Home Size | Typical kW Range | Notes |
|---|---|---|
| Under 1,500 sq ft | 14kW – 18kW | 1-zone HVAC, standard appliances |
| 1,500 – 2,500 sq ft | 18kW – 22kW | 1–2 zone HVAC, standard load |
| 2,500 – 3,500 sq ft | 22kW – 26kW | 2-zone HVAC, likely gas appliances help |
| 3,500 – 5,000 sq ft | 26kW – 36kW | 2+ zone HVAC, larger electrical panel |
| 5,000+ sq ft | 36kW – 80kW+ | Large estate: multiple HVAC zones, pool, EV, etc. |
Important DFW note: These ranges assume standard loads. North Texas homes often have larger HVAC systems than same-square-footage homes in cooler climates. A 2,500 sq ft home in Fort Worth may have a 5-ton system running against 100°F+ ambient temperatures — which draws significantly more power than a 3-ton system in a mild-climate home of the same size. Always verify HVAC tonnage as part of your sizing assessment.
The Single Biggest Variable: Your HVAC System
In a DFW home, your HVAC system is the dominant load. Central air conditioning is the largest single draw in most Texas homes, particularly during summer when the generator is most likely to be running at peak output.
HVAC starting (startup) current is typically 2–3x the running current, which is called the surge or starting load. The generator must be able to handle this surge — not just the steady-state running draw.
| HVAC Size (tons) | Approx. Running kW | Approx. Starting kW Surge |
|---|---|---|
| 2 tons | ~2.5 kW | ~6–8 kW |
| 3 tons | ~3.5 kW | ~8–10 kW |
| 4 tons | ~5 kW | ~12–14 kW |
| 5 tons | ~6 kW | ~14–18 kW |
A home with a 5-ton HVAC system needs a generator that can handle the 14–18 kW startup surge of the air conditioner alone — before adding the rest of the home’s load. This is why undersized generators are a common and expensive mistake.
Other Major Loads to Count
Beyond HVAC, these are the biggest contributors to peak load:
Electric water heater: 4–5 kW (running). If you have a gas water heater, this is a significant savings.
Refrigerator + freezer: 1–2 kW combined (running), with 2–3x startup surge.
Sump pump / well pump: 1–2 kW (running), high startup surge.
Lighting throughout home: 0.5–2 kW depending on bulb type and count.
Home office equipment: 0.5–1.5 kW.
Pool pump: 1–3 kW depending on HP rating.
Electric vehicle charger (Level 2): 7–11 kW — one of the largest single loads, and increasingly common in newer DFW construction.
Electric range or oven: 5–8 kW — if you have gas cooking, this is zero.
The combination of loads running simultaneously during an outage determines your peak demand. Adding these up — accounting for startup surge on motor-driven equipment — gives you your sizing number.
Why Gas Appliances Change the Math
If your home has natural gas appliances — furnace, water heater, cooking range — your generator sizing requirements decrease significantly compared to an all-electric home. Gas appliances continue running during an outage as long as your gas supply is operational; they don’t require generator power.
When we assess a home for generator sizing, we note every gas vs. electric appliance specifically. An all-gas home with the same square footage and HVAC as an all-electric home may need a generator 8–12 kW smaller to achieve the same level of whole-home coverage.
Whole-Home Coverage vs. Essential Circuits
Most generator buyers want whole-home coverage — the generator powers everything, exactly as if the utility were on. That’s the premise of this guide.
Some homeowners opt for partial coverage: a smaller generator that powers essential circuits only (refrigerator, a few lights, one HVAC zone, internet router). This reduces the kW requirement and installation cost. It’s achieved through load management modules that shed non-essential loads when the generator is running at capacity.
If budget is a consideration, partial coverage with a 14–18 kW generator is a legitimate conversation. The trade-off: you’ll need to manually manage some circuits during an extended outage, and certain loads (second HVAC zone, EV charger, pool equipment) may not be available.
Most DFW homeowners at the higher end of the market choose whole-home coverage. We’ll walk through both options on the site visit.
Why Online Calculators Tend to Undersize
Most online generator sizing calculators ask you to check boxes for appliances and return a kW number. The problem:
They assume average startup surges, not actual. Older HVAC equipment, well pumps, and oversized pool pumps can have significantly higher startup currents than the average figures built into the calculator.
They don’t know your panel. An older 100A or 150A main breaker home has a hard ceiling on simultaneous draw that affects sizing differently than a 200A or 400A panel home.
They don’t account for what you’ll actually have on. A Friday evening in August with kids home, pool running, multiple refrigerators, EV charging, and HVAC fighting 105°F is a very different load profile than a Tuesday morning in October.
A professional load calculation — performed during a site visit — measures your actual installed equipment, reviews your panel, notes your gas vs. electric mix, and gives you an accurate sizing recommendation. It costs nothing and takes about 30 minutes.
Generator Models Available at HomeSafe
HomeSafe carries Generac, Kohler, and Champion standby generators across the full residential kW range. A selection of available kW options:
- 14kW, 18kW, 22kW, 24kW, 26kW, 28kW, 30kW, 32kW (Generac)
- 38kW, 40kW, 48kW, 60kW, 80kW (Generac — larger estate / commercial-adjacent)
- 14kW, 20kW, 26kW, 38kW, 48kW, 60kW (Kohler)
- 12.5kW, 22kW (Champion)
Once your load calculation is complete, we’ll match you to the right model across all three brands and show you the installed cost for each option.
See all available models: /products/
Frequently Asked Questions
Is a 22kW generator enough for a 2,500 sq ft home?
For most 2,500 sq ft DFW homes with a single-zone HVAC (3–3.5 tons), yes — a 22kW generator provides whole-home coverage with capacity to spare. Homes with 4-ton+ HVAC, electric water heaters, or additional high-draw equipment should verify with a load calculation.
Can I add a generator later and upsize if I need more power?
Yes, but it’s expensive. The transfer switch, conduit, pad, and permits are all installed for a specific unit. Upsizing later means replacing the generator and potentially the transfer switch. It’s far more cost-effective to size correctly on the first install.
What happens if the generator is undersized during a peak load?
The generator may trip on overload — shutting off to protect itself. In a summer outage, this means losing power during the hottest period. Persistent overloading shortens engine life significantly.
Do I need a bigger generator for a two-story home?
Story count matters less than square footage and HVAC system size. A two-story 2,500 sq ft home with one HVAC zone has similar generator requirements to a single-story home of the same size.
Get a Sizing Recommendation Built Around Your Actual Home
Online calculators give you a ballpark. A HomeSafe site visit gives you the right answer — based on your installed equipment, your panel, your fuel setup, and your usage patterns. The assessment is free and takes about 30 minutes.
Schedule Your Free Site Visit →
Call (817) 439-9009 to talk it through first