Choosing a size
13kW, 17kW or 20kW?
Three capacities, one engine, and a decision that in Texas comes down to air conditioning rather than floor area. Here is what separates them, with the prices published.
The short answer
| Model | Output | What it covers | Equipment |
|---|---|---|---|
| RS13A | 13kW | Essential circuits plus one central AC in a home up to roughly 1,800 sq ft. | $4,286.47 |
| RS17A | 17kW | Most of a 2,000-2,500 sq ft home with load management on the larger AC. | $5,167.05 |
| RS20A | 20kW | Whole-house coverage for a typical 2,500-3,500 sq ft DFW home with two AC systems, using load management. | $5,747.50 |
Equipment only, at the Cummins advertised price, which is the same at every authorized dealer. Installation is quoted separately after a free survey.
Square footage is the wrong unit
Every sizing chart you will find online is indexed on floor area, and in this climate that is close to useless on its own. The load that decides which of these three you need is air conditioning, specifically the moment a compressor starts. A compressor draws several times its running current for the first fraction of a second, and a generator has to absorb that surge without the voltage sagging far enough to stall it.
Two houses of identical size can land on different models. A 2,400 sq ft home with one four-ton system is comfortably inside the RS17A. The same 2,400 sq ft with two systems and a pool pump is a RS20A conversation. It is worth reading what actually happens when a generator starts an air conditioner before you settle on a number, and the sizing calculator will give you a range in a couple of minutes.
What is identical across all three
More than you would expect, which is why the decision is narrower than it looks. All three are the same Cummins QSJ999G engine in the same aluminum enclosure, published at the same 65 dB(A) at 23 feet, running on either natural gas or LP vapor, listed to UL 2200 and installable at 18 inches from the building under NFPA 37. All three carry the same 5 year / 2,000 hour limited warranty.
So you are not buying a better machine as you go up. You are buying more simultaneous load.
What the steps cost
$880.58 of equipment separates the RS13A from the RS17A, and $580.45 separates the RS17A from the RS20A. Installation barely moves between them — all three sit on a similar pad with a similar electrical tie-in, and what actually drives an installed price is the gas line, the distance from your meter, the run to your panel and your city's permit.
That makes stepping up cheaper than most people assume, and it is why we rarely recommend buying the smallest unit that technically fits. The gap between what a house needs today and what it needs after a kitchen remodel or a pool is often one rung.
When a bigger unit is the wrong answer
If the reason you are being pushed up a size is two compressors starting together, the cheaper fix is usually to stop them doing that. A load management module sheds one system for the seconds the other needs to start, and it costs materially less than the step up. We set out both paths in load management or a bigger generator, including the cases where buying the bigger machine genuinely is the better deal.
Above 20kW
These three are the air-cooled range and it stops at 20kW. Above that the line becomes liquid-cooled, starting at 25kW, which is a different machine with a different footprint, sound level and service interval rather than simply a larger version of this one. If your load calculation lands past 20kW, the full Cummins lineup, 13kW to 200kW is the place to look, and every liquid-cooled model, 25kW to 150kW is priced on the site.
Questions
Is 20kW enough for a 3,000 square foot house?
Usually yes, with load management. The RS20A covers a typical 2,500 to 3,500 sq ft DFW home with two air conditioning systems when the two compressors are prevented from starting simultaneously. Square footage is the wrong unit to decide on though — a 3,000 sq ft home with two 5-ton systems and a well pump is a different problem from a 3,000 sq ft home with one 4-ton system. The load calculation at the survey settles it.
What is the real difference between 13kW, 17kW and 20kW?
Roughly, how much air conditioning you can start and how much you can run at once. The 13kW covers essential circuits plus one central AC in a home up to about 1,800 sq ft. The 17kW covers most of a 2,000 to 2,500 sq ft home with load management on the larger AC. The 20kW covers 2,500 to 3,500 sq ft with two AC systems, again using load management. Mechanically they are the same machine — same Cummins QSJ999G engine, same 65 dB(A) published sound level, same enclosure and the same 5 year / 2,000 hour warranty.
Is it worth stepping up a size just in case?
Sometimes, and it is cheaper than people expect: $880.58 of equipment from 13kW to 17kW and $580.45 from 17kW to 20kW. But a bigger generator is not always the right answer to a simultaneity problem — if two compressors starting together is what pushes you up a size, a load management module is usually cheaper than the step. That trade-off is its own question and we cover it separately.
Do the bigger units cost more to install?
Not much, in this range. All three are air-cooled units on a similar pad with a similar electrical tie-in. What moves an installed price is the gas line, the distance from the meter, the run to your panel and your city's permit, not which of these three sits on the pad. The installed bands we quote are $11,000 to $14,000 for 13kW, $12,500 to $15,500 for 17kW and $13,500 to $17,000 for 20kW.
Should I get the model with the transfer switch included?
If your service size suits it, it is usually the cleaner buy. The RS20AC ships with a 200A service-entrance rated, NEMA 3R automatic transfer switch at $6,662.42, against $5,747.50 for the RS20A without one. Service-entrance rated means the switch can serve as your main disconnect, which often simplifies the install. The switch is sized to your electrical service rather than to the generator, so we confirm your service at the survey before specifying it.
We will size it against your actual panel
The survey is free and it produces a load calculation, not a guess from floor area. If the answer is the smaller unit, that is what we will tell you.
Rather just talk to someone?
Leave a number and we will call you. No sales script, no obligation.
Got it. We will call you. If you would rather not wait, ring (214) 957-4307 and ask for whoever is on generators.