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What size generator do I need?

In Texas, air conditioning decides this — not square footage. A 3,000 sq ft house with one AC system needs less generator than a 2,200 sq ft house with two. Answer seven questions and you will get a kilowatt range and the models that fit it.

What size generator for a 2,000, 2,500, 3,000 or 3,500 sq ft Texas home

The short answer, before you run the calculator. These assume a typical DFW house on natural gas with load management, which is how we install the large majority of them. Without load management the requirement rises sharply, so both are shown.

Home size AC systems With load management Typical model Without load management
Up to 2,000 sq ft 1 × 2.5 ton 12 – 14 kW Cummins RS13A — 13kW on gas · $4,419.04 13 – 15 kW (RS17A)
2,001 – 2,500 sq ft 1 × 3.5 ton 15 – 17 kW Cummins RS17A — 17kW on gas · $5,326.86 16 – 19 kW (RS20A)
2,501 – 3,500 sq ft 2 × 3.5 ton 16 – 19 kW Cummins RS20A — 18kW on gas · $5,925.25 27 – 31 kW (RS30)
3,501 – 4,500 sq ft 2 × 5 ton 23 – 27 kW Cummins RS25 — 25kW on gas · $17,622.48 38 – 45 kW (RS50)
4,501 – 6,000 sq ft 3 × 5 ton 25 – 30 kW Cummins RS30 — 30kW on gas · $18,812.69 42 – 50 kW (RS50)

Prices are equipment only. Square footage is a proxy here — the calculator below asks for your actual air conditioning tonnage, which is what really decides the answer. Sizes assume no EV charger, well pump or pool equipment; add those in the calculator.

Size it against your actual loads

Count outdoor condenser units. Most two-story DFW homes have two.
On the condenser data plate, the model number usually encodes it: 048 = 4 ton, 060 = 5 ton. If you are not sure, pick "Not sure" and we will assume 4 ton.
Gas appliances draw almost nothing from a generator. This is where most sizing mistakes happen.
Load management briefly delays the second AC compressor when the first starts. You will not notice it, and it commonly drops the generator by one size.
This matters more than it sounds. The 20kW air-cooled units produce 20kW on propane but only 18kW on natural gas, and most sellers publish only the larger figure. We size against whichever one you will actually burn.

Why air conditioning drives the number in Texas

A generator has to survive the moment a compressor starts, not just the steady load once it is running. An air conditioning compressor draws several times its running current for the first fraction of a second — locked rotor amps — and if the generator cannot cover that surge, the voltage sags, the compressor stalls, and eventually something expensive fails.

That is why a house with two 4-ton systems can need more generator than a much larger house with one. It is also why soft-start modules and load management matter so much here: both attack the surge rather than the steady draw, and both are usually cheaper than moving up a generator size.

What the calculator assumes

These are the actual factors, published so you (or anyone quoting this page) can reproduce the number rather than guess at it:

  • 5kW base household load — refrigeration, lighting, outlets, networking, garage doors. Add 2kW above 3,500 sq ft.
  • 1.2kW running load per ton of air conditioning on the largest system.
  • Secondary AC systems at 75% of the largest, since additional zones are usually smaller — and at 50% of that again under load management, because the module stages them rather than running them flat out.
  • Starting allowance of 2 × tons with load management, where only one compressor startup has to be covered at a time. Without it, 2.4 × tons × the number of systems, capped at two.
  • This is a starting allowance, not full locked-rotor amps. Standby sets are rated for motor starting, so charging full LRA oversizes every result by a size.
  • Standard nameplate values for electric range, dryer, water heater and EV charging. Under load management those are assumed to shed, because that is what a load management module is for.
  • The result is shown as a band of ±8% around the computed figure.

What it cannot know

Your actual panel capacity, how your circuits are grouped, whether your gas meter can carry the additional demand, and what your city requires. Those come out of the survey, and any of them can change the recommendation. Treat this as a starting range, which is exactly how we treat it internally.

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