By the PES Supply field team — updated for the 2026 product lineup

Kohler has been building generators since 1920 — longer than most of today's competitors have existed as companies — and the energy business now operates under the Rehlko name after Kohler Energy's 2024 spinout, with the Kohler brand retained on the products themselves. For buyers, nothing about the hardware changed: same engines, same enclosures, same dealer network. What you get with Kohler is the premium end of the air-cooled standby market and a genuine industrial line behind it, which matters if you're a homeowner who wants the residential unit backed by a company that also powers hospitals.

We sell Kohler alongside Generac and Cummins, and we steer customers to Kohler in specific situations: coastal corrosion exposure (the aluminum enclosure is the best in class), buyers who want the strongest standard warranty in the segment, and anyone who's had a bad experience with the value-tier brands and is done experimenting. This guide covers the lineup, the sizing math, and the honest competitive picture. Cross-shop with our Cummins brand guide and Briggs & Stratton guide.

Kohler Co. entered power generation in 1920 with a 1500-watt lighting plant for rural farms — before most of rural America had utility power to back up. A century later, the energy division spans residential air-cooled units, gaseous commercial sets, and industrial diesels up to 4 megawatts, sold through a dealer network of more than 10,000 locations worldwide. In 2024, Kohler Energy became an independent company under Platinum Equity ownership and rebranded as Rehlko; the products continue under the Kohler name with unchanged engineering, manufacturing in Wisconsin and Mississippi, and warranty backing.

From the counter, the practical effect of the Rehlko transition has been nil — parts flow, warranty processing, and dealer support have continued without a hiccup through 2026. We mention it only because customers see the Rehlko name on documentation and ask. It's the same company making the same machines.

Kohler's engineering culture skews conservative and vertically integrated: the RES line runs Kohler's own OHVI engines (purpose-built for standby duty, not adapted lawn-equipment blocks), the alternators are Kohler-wound, and the enclosures, controllers, and transfer switches come from the same family. When we troubleshoot a Kohler unit, we're calling one company, not arbitrating between an engine maker and a generator assembler. That single-throat-to-choke structure is worth something at 2 a.m. during an ice storm.

Generator sizing is NEC 702 territory: optional standby systems must carry the load they're assigned, and the honest way to size is a load calculation, not a guess based on square footage. Here's the workflow we run with customers, using a real 2,800 sq ft all-electric home as the example.

Two rules of thumb that survive contact with reality. First: motor starting dominates. A 4-ton compressor without a soft starter can demand 15+ kVA for a few hundred milliseconds; air-cooled standby units have solid motor-starting capability, but pairing the A/C with a soft-start module is the cheapest way to keep a 20 kW unit on a large home. Second: load management is the multiplier. Kohler's load-control accessories shed the water heater and range during generator operation, which is how a 20RESCL covers a house that would otherwise want a 26RES or a liquid-cooled unit.

Fuel supply is the other half of sizing, and it's where we see the most install failures. The numbers below are why a gas-pipe upsizing is often part of the quote.

An LP install that vaporizes fuel faster than the tank can supply it will stumble exactly when the house needs it most — cold weather, full load, tank below a third. We spec 500-gallon tanks for 20 kW+ LP installs as a matter of policy. The plumbing details are in our transfer switch wiring guide's companion notes and the transfer switch explainer.

The honest summary: Generac wins on unit volume, price, and the 28 kW top end; Kohler wins on enclosure durability, engine pedigree, and dealer depth; Briggs counters with the 10-year warranty at a lower price point; Cummins owns the premium-quiet niche with a smaller residential dealer footprint. We sell all four. When a customer is within sight of salt water, planning to keep the house 15+ years, or simply wants the machine their grandchildren will inherit, we quote the Kohler. For whole-home strategy beyond the generator itself — battery hybrid approaches, critical-loads panels — see battery backup vs generator and our whole-house generator overview.

Kohler's standard residential warranty is 5 years covering parts, labor, and travel — the travel clause matters in rural counties where the nearest dealer is 90 minutes out. The design-validation program behind the RES line tests engines to a 20-year residential duty cycle: start-stop cycling, load banks, and extended-run endurance that mimics decades of outage duty. Most competitors test to a "standard" cycle they don't publish.

Service intervals are conventional: oil and filter at 150 hours or annually, valve adjustment on schedule, battery every three to four years. The units exercise weekly by default (we recommend a 12-minute no-load exercise, mid-week, mid-day — neighbors remember generators that exercise at 7 a.m. Sundays). Every Kohler we sell leaves with the maintenance schedule taped inside the transfer switch door, because the number-one killer of standby generators isn't manufacturing defects — it's neglected oil and dead starting batteries.

For wire sizing between the generator, ATS, and panel, the ampacity tables in our NEC wire sizing guide apply directly — a 20 kW unit at 240V is an 83A continuous-class source, and the conductors and breaker need to be sized to the generator's nameplate and NEC 445/702, not to the load calc alone.

Quote transparency is rare in this trade, so here's the real breakdown we give customers for a 20RESCL turnkey install in our market. Prices move with gas-line length and panel condition, but the proportions hold:

Where quotes blow past this range: meter upgrades the utility schedules on their own calendar, panels that need replacement before the ATS can land, and LP conversions where a new 500-gallon tank gets set. Get the gas path and the panel condition assessed before signing anything — those two items account for nearly every cost overrun we've watched customers endure with other installers.

Standby generators fail from neglect, not engineering. The schedule we tape inside every transfer switch: weekly 12-minute no-load exercise (automatic), oil and filter at 150 run-hours or annually, air filter and spark plugs annually, battery test every six months with replacement at year three to four, valve clearance per the OHVI service schedule, and an annual full-load test where the unit carries the real house for thirty minutes while someone watches gas pressure and output voltage. OnCue Plus monitoring catches missed exercises and low-battery conditions between service visits — it's the cheapest insurance in the whole system.

The failure modes are remarkably consistent across brands, and nearly all of them are install-side, not machine-side. Undersized gas piping tops the list — a generator that can't get fuel at full load is a decoration. Second is placement: units jammed against the structure or under soffit vents to save conduit money, creating exhaust and service-clearance problems the inspector will catch if the CO doesn't. Third is skipping the load calculation entirely and selling whatever kW tier the homeowner's neighbor bought. Fourth — and this one costs people the most grief — is commissioning without a full-load test, so the first real outage is also the first real test. Finally: no maintenance plan. A $12,000 machine with a dead starting battery fails exactly like a $4,000 machine with a dead battery. Sell the maintenance agreement or teach the customer the schedule; one of the two has to happen.

One more that deserves its own paragraph: customers who size the generator to survive the last outage instead of the next one. The last outage was eight hours in mild weather; the next one is a three-day ice storm with the furnace running flat out. Design for the severe case at the site's actual design temperature, because an air-cooled engine's output and an LP tank's vaporization both sag exactly when the load peaks. The load calc in Section 3 with a cold-weather margin is cheap insurance against the expensive version of this lesson.

And a boundary worth stating plainly: if the home's backup need is four hours of fridge-and-lights a couple of times a year, a standby generator is overkill — a battery system or a quality portable is the honest recommendation, and we make it. Standby units earn their keep when outages run long, loads run heavy (well pumps, medical equipment, whole-home HVAC), or nobody is home to wheel out a portable and run extension cords. Right-sizing the solution to the actual risk profile is the whole job.

• Kohler Energy (Rehlko) published specifications: 14RES, 20RESCL, 26RES, KD series, PRO5.2 (2025–2026 revisions)
• NEC 2023 Articles 702 (optional standby systems), 445 (generators), 250 (grounding for separately derived systems)
• NFPA 110 — emergency and standby power systems (KD series life-safety applications)
• PES Supply internal sizing worksheets and installer-partner field reports, 2022–2026

• Cummins Brand Guide for Standby Professionals
• Briggs & Stratton Brand Guide
• Transfer Switch Wiring Guide
• Battery Backup vs Generator: Which Backup Strategy Wins
• Best Backup Generator for Home
• NEC Wire Sizing Guide: Ampacity Charts for Solar & Generator Installs